In this paper a 0.13 μm CMOS front-end for drift chambers is presented. The front-end presents characteristics of low power consumption, which are well-suited in order to implement the cluster counting technique for particles identification. The front-end consists of a Variable Gain Amplifier (VGA) with 0, 10 and 20 dB gain steps and 1 GSa/s 6 bits Analog to Digital Converter (ADC). The VGA power consumption has been optimized according to the selected gain setting. The VGA power consumption is 8.4 mA, 9.4 mA, 10.6 mA for 0, 10, 20 dB gain, respectively.

We propose a fast acquisition and elaboration system in order to process signals coming from Drift Chambers. The system is made of an analog Front End, designed in our laboratory for signal acquisition and a Demo Board by Texas Instruments for data elaboration. The Front End electronics is a multistage amplifier board based on high performance commercial devices. Texas Instruments board includes an Analog to Digital Converter and a FPGA (Field Programmable Gate Array) in order to implement algorithm for Cluster Counting and Timing purposes.

We developed a high performance full chain for drift chamber signals processing. The Front End electronics is a multistage amplifier board based on high performance commercial devices. In addition a fast readout algorithm for Cluster Counting and Timing purposes has been implemented on a Xilinx-Virtex 4 core FPGA. The algorithm analyzes and stores data coming from a Helium based drift tube and represents the outcome of balancing between efficiency and high speed performance.

Front End (FE) Electronics plays an essential role in Drift Chambers (DC) for time resolution and, therefore, spatial resolution. The use of cluster timing techniques, by measuring the timing of all the individual ionization clusters after the first one, may enable to reach resolutions even below 100 μm in the measurement of the impact parameter. To this purpose, a Front End Electronics with a wide bandwidth and low noise is mandatory in order to acquire and amplify the drift chamber signals.

MEG Experiment Upgrade proposes a major improvement [1] of the sensitivity in the μ →eγ decay [2]. In particular the positron tracking will be performed by means of an upgrade of MEG Drift Chamber that consists in a cylindrical wire drift chamber, with the axis parallel to the muon beam, inspired to the one used in the KLOE experiment [3]. The new tracker, currently under costruction, can achieve a resolution of 100 μm in the measurement of the drift distance to the anode wires. Improving the resolution imposes a high speed and high performance Front End Electronics for signal acquisition. © 2015 IEEE.

A search for the decay μ+→e+γ, performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of BR(μ+→e+γ)2.8×10^−11 (90% C.L.). This corresponds to the measurement of positrons and photons from ~10^14 stopped μ+ decays by means of a superconducting positron spectrometer and a 900 litre liquid xenon photon detector.

The Extreme Energy Events (EEE) Project is a Centro Fermi - CERN - INFN - MIUR Collaboration Project for the study of extremely high energy cosmic rays, which exploits the Multigap Resistive Plate Chamber (MRPC) technology. The excellent time resolution and good tracking capability of this kind of detector allows us to study Extensive Air Showers (EAS) with an array of MRPC telescopes distributed across the Italian territory. Each telescope is installed in a high school, with the further goal to introduce students to particle and astroparticle Physics. The status of the experiment and the results obtained are reported.

The Extreme Energy Events (EEE) Project is a Centro Fermi - CERN - INFN - MIUR Collaboration Project, for the study of extremely high-energy cosmic rays, which exploits the Multigap Resistive Plate Chamber (MRPC) technology. The excellent time resolution and good tracking capability of this detector allows us to study Extensive Air Showers (EAS) with an array of telescopes distributed all over the Italian territory. Each telescope is installed in a High School, with the additional goal to introduce students to particle and astroparticle Physics. The EEE array is composed, so far, of 47 telescopes, each made of three MRPC planes, spanning more than 10 degrees in latitude and 11 in longitude, organized in clusters and single telescope stations. The status of the experiment and the results, obtained during two recent coordinated data taking periods, will be reported. The observation of Forbush decreases, coincidence events among different telescopes and the muon decay, using more than 5 billion tracks collected in the last few months, are of particular interest.

Modern High Energy Physics experiments for the search of extremely rare processes require high resolutions (order of 50-200 keV/c) tracking systems for particle momenta in the range of 50-300 MeV/c, dominated by multiple scattering contributions. We will describe a newly developed construction technique for ultra-low mass, high granularity Drift Chambers fulfilling this goal. These techniques have been successfully implemented at INFN-Lecce and University of Salento and are currently being used for the construction of the Drift Chamber of the MEG upgrade experiment.

Modern experiments for the search of extremely rare processes require high resolutions (order of 50–200 keV/c) tracking systems for particle momenta in the range of 50–300 MeV/c, dominated by multiple scattering contributions. We will present a newly developed construction technique for ultra-low mass Drift Chambers fulfilling this goal. It consists of (1) a semiautomatic wiring machine with a high degree of control over wire mechanical tensioning (better than 0.2 g) and over wire positioning (of the order of 20 μm) for simultaneous wiring of multi-wire layers; (2) a contact-less IR laser soldering tool designed for a feed-through-less wire anchoring system; (3) an automatic handling system for storing and transporting the multi-wire layers to be placed over the drift chamber end-plates. These techniques have been successfully implemented at INFN-Lecce and University of Salento and are currently being used for the construction of Drift Chamber of the MEG (μ→eγ) upgrade experiment.

A new cylindrical drift chamber is currently under construction for the MEG II experiment. The chamber is meant to track low momentum positrons from μ+ decays to search for μ+→e+γ events. The detector is segmented in very small drift cells, placed in stereo configuration and operated in a helium–isobutane gas mixture. The use of thin aluminium wires and light gas mixture set the total radiation length of the chamber to only 1.6×10−3 X0 per track turn allowing for a momentum resolution of ~120 keV/c.

A low noise, high speed board designed for drift chamber signals processing has been developed. The Front End electronics is a multistage amplifier based on high performance commercial devices. In addition, a fast readout algorithm for Cluster Counting and Timing purposes has been implemented on a Xilinx-Virtex 4 core FPGA. The algorithm analyzes and stores data coming from a Helium based drift cell and represents the outcome of balancing between efficiency and high speed performance.

In this paper the first study of the upward going events detected by the telescopes of the Extreme Energy Event (EEE) project is reported. The EEE project consists of a detector array of Multigap Resistive Plate Chambers located at selected sites on the Italian territory. During autumn 2014 the first coordinated data taking period took place and around one billion candidate tracks were collected. Among them, of particular interest is the sample of particles which cross the telescopes from below. The results obtained demonstrate that the EEE telescopes can distinguish the electrons produced as decay products of cosmic muons stopped in the ground, or in the last chamber of the telescopes themselves, confirming the excellent performance of the system for the investigation of intriguing cosmic phenomena

Ultra-low mass and high granularity Drift Chambers seems to be a better choice for modern HEP experiments, to achieve a good momentum resolution on the charged particle. We present how, in Helium based gas mixture, by counting and measuring the arrival time of each individual ionization cluster and by using statistical tools, it is possible to reconstruct a bias free estimate of the impact parameter and a more discriminant Particle Identification.

ARGO-YBJ is an extensive air shower detector located at the Yangbajing Cosmic Ray Laboratory (4300 m a.s.l., 606 g cm−2 atmospheric depth, Tibet, China). It is made by a single layer of Resistive Plate Chambers (RPCs, total surface 6700 m2) grouped into 153 units called “clusters”. The low energy threshold of the experiment is obtained using the ”scaler operation mode”, counting all the particles hitting the detector without reconstruction of the shower size and arrival direction. For each cluster the signals generated by these particles are put in coincidence in a narrow time window (150 ns) and read by four independent scaler channels, giving the counting rates of channel 1, 2, 3 and 4 hits. The study of these counting rates pointed out a different behavior of channel 1 respect to the higher multiplicity channels: while the MC simulations can account fairly well for the coincident counting rates, the expectation for channel 1 is sensibly less than the measured value. Moreover, the regression coefficient with the atmospheric pressure for channel 1 is also about half of the value measured for the coincident counting rates: seemingly half of these counts did not cross the atmosphere. Measurements of the natural radioactivity background in the air of the detector hall and a MC simulation to estimate its contribution on our counting rates are presented and discussed.

The MEG experiment at PSI searches for the decay μ→eγ at a level of ≈10^−13 on the branching ratio BR(μ→eγ/μ→tot), well beyond the present experimental limit (BR≤1.2×10^−11) and is sensitive to the predictions of SUSY-GUT theories. To reach this goal the experiment uses one of the most intense continuous surface muon beams available (≈10^8μ/s) and relies on advanced technology (LXe calorimetry, a gradient-field superconducting spectrometer as well as flexible and powerful trigger and acquisition systems). In order to maintain the highest possible energy, time and spatial resolutions for such detector, frequent calibration and monitoring, using a Cockcroft–Walton proton accelerator, are required. The proton beam is brought to the centre of MEG by a special bellows insertion system and travels in a direction opposite to the one of the normal μ-beam. Protons interact with a lithium tetraborate (Li2B4O7) nuclear target and produce one γ (17.6 MeV) from the reaction 3-7 Li(p, γ)8-4 or two coincident γs (11.67 and 4.4 MeV) from the reaction 11-5 B(p, γ)12-6 C*. The 17.6 MeV γ is used for calibrating and monitoring the LXe calorimeter (σEγ/Eγ=3.85±0.15% at 17.6 MeV) while the coincident 11.67 and 4.4 MeV γs are used to measure the relative timing of the calorimeter and the spectrometer timing counters (σ_delta_t=0.450±0.015ns).

The charge readout of Resistive Plate Chambers (RPCs) is implemented in the ARGO-YBJ experiment to measure the charged particle density of the shower front up to 10^4 / m^2, enabling the study of the primary cosmic rays with energies in the ‘‘knee’’ region. As the first time for RPCs being used this way, a telescope with RPCs and scintillation detectors is setup to calibrate the number of charged particles hitting a RPC versus its charge readout. Air shower particles are taken as the calibration beam. The telescope was tested at sea level and then moved to the ARGO-YBJ site for coincident operation with the ARGO-YBJ experiment. The charge readout shows good linearity with the particle density in the dynamic range (up to 200/m^2).

The ARGO-YBJ experiment is a full coverage array of Resistive Plate Chambers (RPCs) with an active area of 5800 m2. In order to eliminate the response difference of the charge readout from the RPCs, a calibration procedure is carried out with the iso-gradient method. This method also allows the extension of the absolute calibration with the muon telescope including scintillation detectors to all the RPCs in the array. The overall systematic uncertainty in measurements of the number of particles by the RPCs is 10.7%. In general, the method gives results consistent with those from a totally different approach also used in the experiment.

Low pressure helium/hydrocarbons mixtures are a key ingredient for next generation ultra-light drift chambers. Besides the obvious advantage of limiting the contribution to the momentum measurement due to multiple scattering, the operation at low pressure allows for a broad range of the drift chamber working parameters like drift velocity, diffusion, specific ionization and gas gain. Low pressure operation is of particular advantage for experiments where the tracking detector operates in vacuum. We present our campaign to characterize electron drift, primary ionization yield, gas gain, stability and the relative spatial resolution in helium based mixtures at absolute pressures down to 100 mbar.

CORAM (COsmic RAy Mission) is an outreach program carried out by INFN and the University of Salento in close collaboration with high schools. Students and their teachers are involved in the design, construction, test and operation of detectors for the measurement of several properties of the cosmic ray flux. The results of a set of measurements, made with a first detector prototype at different altitudes and underground, will be described

The main scientific goals of the ARGO-YBJ experiment are ray astronomy with a few hundreds GeV energy threshold and cosmic ray physics below and around the knee of the primary energy spectrum (10**12−10**16 eV), where the transition from direct to indirect measurement techniques takes place. The ARGO-YBJ experiment, located at the Cosmic Ray Observatory of Yangbajing (Tibet, P.R. of China, 4 300 m a.s.l.), is an unconventional Extensive Air Shower array of about 6,700 m2 of active area, the only one exploiting the full-coverage technique at very high altitude currently in operation. The detector space-time granularity, performance and location offer a unique chance to make a detailed study of the structure of cosmic ray showers, in particular of the hadronic component. In this work we will focus on the main experimental results concerning cosmic ray and hadronic interaction physics: primary cosmic ray energy spectrum, antiproton over proton ratio, anisotropy in the cosmic ray flux and proton-air cross-section. Moreover, the possible data analysis improvements based on the use of all detailed information on the shower front (curvature, time width, rise time and so on), as well as the extension of the investigable energy range, allowed by the analog RPC readout, will be pointed out.

The Extreme Energy Events Project (EEE Project) is an innovative experiment to study very high energy cosmic rays by means of the detection of the associated air shower muon component. It consists of a network of tracking detectors installed inside Italian High Schools. Each tracking detector, called EEE telescope, is composed of three Multigap Resistive Plate Chambers (MRPCs). At present, 43 telescopes are installed and taking data, opening the way for the detection of far away coincidences over a total area of about 3 × 10^5 km^2. In this paper we present the Monte Carlo simulations that have been performed to predict the expected coincidence rate between distant EEE telescopes.

The ARGO-YBJ air shower detector monitored the Crab Nebula gamma-ray emission from 2007 November to 2013 February. The integrated signal, consisting of ∼3.3×10^5 events, reached the statistical significance of 21.1 standard deviations. The obtained energy spectrum in the energy range 0.3–20 TeV can be described by a power law function dN/dE = I_0 (E / 2TeV)^{−α}, with a flux normalization I_0 = (5.2±0.2)×10−12 photons cm−2 s−1 TeV−1 and α=2.63±0.05, corresponding to an integrated flux above 1 TeV of 1.97×10−11 photons cm−2 s−1. The systematic error is estimated to be less than 30% for the flux normalization and 0.06 for the spectral index. Assuming a power law spectrum with an exponential cutoff dN/dE=I_0 (E/2TeV)^{−α} exp (−E/E_cut), the lower limit of the cutoff energy E_cut is 12 TeV, at 90% confidence level. Our extended data set allows the study of the TeV emission over long timescales. Over five years, the light curve of the Crab Nebula in 200-day bins is compatible with a steady emission with a probability of 7.3×10−2. A correlated analysis with Fermi-LAT data over ∼4.5 yr using the light curves of the two experiments gives a Pearson correlation coefficient r=0.56±0.22. Concerning flux variations on timescales of days, a “blind” search for flares with a duration of 1–15 days gives no excess with a significance higher than four standard deviations. The average rate measured by ARGO-YBJ during the three most powerful flares detected by Fermi-LAT is 205±91 photons day−1, consistent with the average value of 137±10 day−1.

Detecting and monitoring emissions from flaring gamma-ray sources in the very-high-energy (VHE, > 100 GeV) band is a very important topic in gamma-ray astronomy. The ARGO-YBJ detector is characterized by a high duty cycle and a wide field of view. Therefore, it is particularly capable of detecting flares from extragalactic objects. Based on fast reconstruction and analysis, real-time monitoring of 33 selected VHE extragalactic sources is implemented. Flares exceeding a specific threshold are reported timely, hence enabling the follow-up observation of these objects using more sensitive detectors, such as Cherenkov telescopes.

The Extreme Energy Events project (EEE) is aimed to study Extensive Air Showers (EAS) from primary cosmic rays of more than 10^18 eV energy detecting the ground secondary muon component using an array of telescopes with high spatial and time resolution. The second goal of the EEE project is to involve High School teachers and students in this advanced research work and to initiate them in scientific culture: to reach both purposes the telescopes are located inside High School buildings and the detector construction, assembling and monitoring - together with data taking and analysis - are done by researchers from scientific institutions in close collaboration with them. At present there are 42 telescopes in just as many High Schools scattered all over Italy, islands included, plus two at CERN and three in INFN units. We report here some preliminary physics results from the first two common data taking periods together with the outreach impact of the project.

The energy spectrum of cosmic Hydrogen and Helium nuclei has been measured below the so-called knee by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber (RPC) array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy resolution of about 25% is achieved throughout the whole energy range (100-700 TeV). The observed energy spectrum is compatible with a single power law with index gamma = -2.63 +- 0.06.

The geomagnetic field causes not only the east-west effect on primary cosmic rays but also affects the trajectories of the secondary charged particles in the shower, causing their lateral distribution to be stretched. Thus, both the density of the secondaries near the shower axis and the trigger efficiency of detector arrays decrease. The effect depends on the direction of the showers, thus, introducing a modulation in the measured azimuthal distribution. The azimuthal distribution of the events collected by the ARGO-YBJ detector is deeply investigated for different zenith angles in light of this effect.

The Extreme Energy Events (EEE) Project is devoted to the study of extremely high energy cosmic rays by means of an array of particle detectors distributed all over the Italian territory. Each element of the array (called telescope in the following) is installed in a High School, with the further goal to introduce students to particle and astroparticle physics, and consists of three Multigap Resistive Plate Chambers (MRPC), that have excellent time resolution and good tracking capability. In this paper the first results on the detection of extensive air showers by means of time coincidences between two telescopes are presented

The Extreme Energy Events (EEE) Project is an experiment for the detection of Extensive Atmospheric Showers of energy greater than 1011 eV. It consists of an array of telescopes hosted in High Schools spread on the Italian territory, each made of three Multigap Resistive Plate Chambers very similar to the ones built for the Time Of Flight system of the ALICE experiment at CERN. The telescopes are managed and constructed at CERN by teams of students and teachers: this peculiarity enhances the scientific relevance of its goals with an effective outreach action. The experiment took a first coordinated data taking (“Pilot-Run”) in fall 2014 and another (“Run1”) from February to April 2015. About thirty telescopes took data at the same time and more than 5 billions of cosmic ray events have been collected. Data were transmitted to the CNAF – the biggest Italian storage and computing center managed by INFN – to be reconstructed and analyzed. In this presentation an overall description of the experiment will be given and the most recent results will be shown. In particular we have a first set of measurements of the coincidences in pairs of telescopes even more than 1 km apart, and a study of variations with time of the muon cosmic flux, related on astrophysical phenomena like Forbush decreases.

We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1−100 GeV in coincidence with the prompt emission detected by satellites, using the Astrophysical Radiation Ground-based Observatory at YangBa-Jing ARGO-YBJ). With its big active surface (6700 m 2) and large field of view (2 sr) the ARGO-YBJ air shower detector is particularly suitable to detect unpredictable and short duration events such as GRBs. The search has been performed using the single particle technique in time coincidence with satellite detections both for single events and for the piling up of all the GRBs in time and in phase. Between November 2004 and June 2010 115 GRBs, detected by different satellites (mainly Swift and Fermi), occurred within the field of view of ARGO-YBJ. For 94 of these we searched for a counterpart in the ARGO-YBJ data finding no statistically significant emission. Search methods and results are discussed.

In 2008 the blazar Markarian 421 entered a very active phase and was one of the brightest sources in the sky at TeV energies, showing frequent flaring episodes. Using the data of ARGO-YBJ, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at gamma ray energies E > 0.3 TeV during the whole year. The observed flux was variable, with the strongest flares in March and June, in correlation with X-ray enhanced activity. While during specific episodes the TeV flux could be several times larger than the Crab Nebula one, the average emission from day 41 to 180 was almost twice the Crab level, with an integral flux of (3.6±0.6) × 10-11 photons cm-2 s-1 for energies E > 1 TeV, and decreased afterwards. This paper concentrates on the flares occurred in the first half of June. This period has been deeply studied from optical to 100 MeV gamma rays, and partially up to TeV energies, since the moonlight hampered the Cherenkov telescope observations during the most intense part of the emission. Our data complete these observations, with the detection of a signal with a statistical significance of 3.8 standard deviations on June 11-13, corresponding to a gamma ray flux about 6 times larger than the Crab one above 1 TeV. The reconstructed differential spectrum, corrected for the intergalactic absorption, can be represented by a power law with an index = -2.1+0.7-0.5 extending up to several TeV. The spectrum slope is fully consistent with previous observations reporting a correlation between the flux and the spectral index, suggesting that this property is maintained in different epochs and characterizes the source emission processes.

The ARGO-YBJ experiment is an Extensive Air Shower detector which combines high altitude location (Tibet, P.R. China, 4300 m a.s.l.) and full coverage with Resistive Plate Counters, resulting in an energy threshold of a few hundred GeV. The large eld of view (2 sr) and high duty cycle allow the continuous monitoring of the Northern sky, searching for unknown sources and unpredictable events, such as ares in blazar emissions or high energy Gamma Ray Bursts. In this paper we will present some results obtained in gamma-ray astronomy with the ARGO-YBJ experiment.

ARGO-YBJ is a full coverage air shower array located at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm2) recording data with a duty cycle 85% and an energy threshold of a few hundred GeV. In this paper the latest results in Gamma-Ray Astronomy are summarized.

In this paper we report on the observations of TeV gamma ray sources performed by the air shower detector ARGO-YBJ. The objects studied in this work are the blazar Markarian 421 and the extended galactic source MGROJ1908+06, monitored during 2 years of operation. Mrk421 has been detected by ARGO-YBJ with a statistical significance of 11 standard deviations. The observed TeV emission was highly variable, showing large enhancements of the flux during active periods. The study of the spectral behaviour during flares revealed a positive correlation of the hardness with the flux, as already reported in the past by the Whipple telescope, suggesting that this is a long term property of the source. ARGO-YBJ observed a strong correlation between TeV gamma rays and the X-ray flux measured by RXTM/ASM and SWIFT/BAT during the whole period, with a time lag compatible with zero, supporting the one-zone SSC model to describe the emission mechanism. MGROJ1908+06 has been detected by ARGO-YBJ with 5 standard deviation of significance. From our data the source appears extended and the measured extension is ext=0.48+0.26−0.28, in agreement with a previous HESS observation. The average flux is in marginal agreement with that reported by MILAGRO, but significantly higher than that obtained by HESS, suggesting a possible flux variability.

In 2008, the blazar Mrk421 entered in a very active phase and was one of the brightest sources in the sky at TeV energies, showing strong and frequent flaring. We searched for gamma-ray emission at energies E>0.8 TeV during the whole 2008 with the ARGO-YBJ experiment, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet, P.R. China). The observed signal is not constant and in correlation with X-ray measurements. The average emission, during the active period of the source, was about twice the Crab Nebula level. This paper concentrates on 2008 June when the Mrk421 flaring activity has been studied from optical to 100 MeV gamma rays, and only partially up to TeV energies, since the moonlight hampered the Cherenkov telescope observations after 8 June. Our data complete these observations, with the detection of a second flare of intensity of about 7 Crab units on June 11-13, with a statistical significance of 4.2 standard deviations. The observed flux is consistent with a prediction made in the framework of the Synchrotron Self-Compton model, in which the flare is caused by a rapid acceleration of leptons in the jet.

The ARGO-YBJ experiment is a multipurpose detector exploiting the full coverage approach at very high altitude. The apparatus, in stable data taking since November 2007 with an energy threshold of a few hundreds of GeV and a duty-cycle > 85%, is located at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm2). A number of interesting results are available in cosmic ray physics and in gamma-ray astronomy after the first 3 years of stable data taking. In this paper gamma-ray astronomy results are summarized.

The extended TeV gamma-ray source ARGO J2031+4157 (or MGRO J2031+41) is positionally consistent with the Cygnus Cocoon discovered by Fermi-LAT at GeV energies in the Cygnus superbubble. Reanalyzing the ARGO-YBJ data collected from 2007 November to 2013 January, the angular extension and energy spectrum of ARGO J2031+4157 are evaluated. After subtracting the contribution of the overlapping TeV sources, the ARGO-YBJ excess map is fitted with a two-dimensional Gaussian function in a square region of 10° × 10°, finding a source extension σ_ext = 1.8 ± 0.5 defrees. The observed differential energy spectrum is dN/dE = (2.5 ± 0.4) × 10^{–11} (E/1 TeV)^{–2.6 ± 0.3} photons cm–2 s–1 TeV–1, in the energy range 0.2-10 TeV. The angular extension is consistent with that of the Cygnus Cocoon as measured by Fermi-LAT and the spectrum also shows a good connection with the one measured in the 1-100 GeV energy range. These features suggest to identify ARGO J2031+4157 as the counterpart of the Cygnus Cocoon at TeV energies. The Cygnus Cocoon, located in the star-forming region of Cygnus X, is interpreted as a cocoon of freshly accelerated cosmic rays related to the Cygnus superbubble. The spectral similarity with supernova remnants (SNRs) indicates that the particle acceleration inside a superbubble is similar to that in an SNR. The spectral measurements from 1 GeV to 10 TeV allows for the first time to determine the possible spectrum slope of the underlying particle distribution. A hadronic model is adopted to explain the spectral energy distribution.

The ARGO-YBJ experiment detects extensive air showers in a wide energy range by means of a full-coverage detector which is in stable data taking in its full configuration since November 2007 at the YBJ International Cosmic Ray Observatory (4300 m a.s.l., Tibet, People’s Republic of China). In this paper the measurement of the light-component spectrum of primary cosmic rays in the energy region 5-200 TeV is reported. The method exploited to analyze the experimental data is based on a Bayesian procedure. The measured intensities of the light component are consistent with the recent CREAM results and higher than that obtained adding the proton and helium spectra reported by the RUNJOB experiment.

Distributions of secondary cosmic muons were measured by the Multigap Resistive Plate Chambers (MRPC) telescopes of the Extreme Energy Events (EEE) Project, spanning a large angular and temporal acceptance through its sparse sites, to test the possibility to search for any anomaly over long runs. After correcting for the time exposure and geometrical acceptance of the telescopes, data were transformed into equatorial coordinates, and equatorial sky maps were obtained from different sites on a preliminary dataset of 110M events in the energy range at sub-TeV scale.

ARGO-YBJ is an air shower detector array with a fully covered layer of Resistive Plate Chambers. It is operated with a high duty cycle and a large field of view. It monitors continuously the northern sky at energies above 0.3 TeV. In this paper, we report a long-term monitoring of Mrk 421 over the period from November 2007 to February 2010. Meanwhile, this source was observed by the satellite-borne experiments RXTE and Swift in the X-ray band. Mrk 421 was very active especially in the first half of 2008. Many flares are observed in both X-ray and gamma-ray bands simultaneously. The gamma-ray flux observed by ARGO-YBJ has a clear correlation with the X-ray flux. No lag longer than 1 day between the X-ray and gamma-ray photons is found. The evolution of the spectral energy distribution is investigated by measuring indices at four different flux levels. Hardening of the spectra is observed in both X-ray and gamma-ray bands. The gamma-ray flux increases quadratically with the simultaneously measured X-ray flux. All these observational results strongly favor the synchrotron self-Compton process as the underlying radiative mechanism.

As one of the brightest active blazars in both X-ray and very high energy γ-ray bands, Mrk 501, is very useful for physics associated with jets from active galactic nuclei. The ARGO-YBJ experiment has monitoredMrk 501 for γ-rays above 0.3 TeV since 2007 November. The largest flare since 2005 was observed from 2011 October and lasted until about 2012 April. In this paper, a detailed analysis of this event is reported. During the brightest γ-ray flaring episodes from 2011 October 17 to November 22, an excess of the event rate over 6σ is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the γ -ray flux above 1 TeV by a factor of 6.6 ± 2.2 from its steady emission. In particular, the γ -ray flux above 8 TeV is detected with a significance better than 4σ. Based on time-dependent synchrotron self-Compton (SSC) processes, the broadband energy spectrum is interpreted as the emission from an electron energy distribution parameterized with a single power-law function with an exponential cutoff at its high-energy end. The average spectral energy distribution for the steady emission is well described by this simple one-zone SSC model. However, the detection of γ -rays above 8 TeV during the flare challenges this model due to the hardness of the spectra. Correlations between X-rays and γ -rays are also investigated.

The ARGO-YBJ detector layout (a full coverage Resistive Plate Chamber, RPC, carpet), features (high resolution space-time pixels) and location (about 600g/cm2 of atmospheric depth) offer a unique opportunity for a detailed study of several characteristics of the hadronic component of the cosmic ray flux in the 1012-1015 eV energy range. The analog readout of the RPC signals indeed provides a powerful tool to study, with unprecedented resolution and without saturation, the extensive air shower space-time structure very close to its axis. The distribution of charged particles at ground and the time structure of the shower front allow estimating the shower age at the detection level independently from the primary mass. Furthermore the truncated size, measured within few meters from the core, gives a reliable energy measurement without biases introduced by finite detector effects. Fluctuations are also reduced thanks to the proximity of the shower maximum to the high altitude detection level. These features allows mass composition studies with an EAS detector in an energy region where a comparison with space or balloon born experiments are now possible for the first time, thus giving a further cross checks on the systematics of the adopted analysis procedures. Moreover, measurements of the proton-air cross section, of the particle distribution close to the shower axis, etc., give new inputs, in the very forward region, to the hadronic interaction models currently used for the study of the cosmic ray flux and its origin up to the highest energies.

The Sun blocks cosmic-ray particles from outside the solar system, forming a detectable shadow in the sky map of cosmic rays detected by the ARGO-YBJ experiment in Tibet. Because the cosmic-ray particles are positively charged, the magnetic field between the Sun and the Earth deflects them from straight trajectories and results in a shift of the shadow from the true location of the Sun. Here, we show that the shift measures the intensity of the field that is transported by the solar wind from the Sun to the Earth.

A muon decay accompanied by a photon through the inner Bremmstrahlung process (μ→eνν¯γ, radiative muon decay) produces a time-correlated pair of positron and photon which becomes one of the main backgrounds in the search for μ→eγμ→eγ decay. This channel is also an important probe of timing calibration and cross-check of whole the experiment. We identified a large sample (∼ 13000) of radiative muon decays in MEG data sample. The measured branching ratio in a region of interest in the μ→eγ search is consistent with the standard model prediction. It is also the first measurement of the decay from polarized muons. The precision measurement of this mode enables us to use it as one of the normalization channels of μ→eγ decay successfully reducing its uncertainty to less than 5%.

Cosmic ray antiprotons provide an important probe for the study of cosmic ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. The ARGO-YBJ experiment is observing the Moon shadow with high statistical significance at an energy threshold of a few hundred GeV. Using all the data collected until November 2009, we set two upper limits on the ¯p/p flux ratio: 5% at an energy of 1.4 TeV and 6% at 5 TeV with a confidence level of 90%. In the few-TeV range the ARGO-YBJ results are the lowest available, useful to constrain models for antiproton production in antimatter domains.

Cosmic ray antiprotons provide an important probe for the study of cosmic-ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. Cosmic rays are hampered by the Moon, therefore a deficit of cosmic rays in its direction is expected (the so-called Moon shadow). The Earth–Moon system acts as a magnetic spectrometer. Infact, due to the geomagnetic field the center of the Moon shifts westward by an amount depending on the primary cosmic ray energy. Paths of primary antiprotons are therefore deflected in an opposite sense in their way to the Earth. This effect allows, in principle, the search of antiparticles in the opposite direction of the observed Moon shadow. The ARGO-YBJ experiment, in stable data taking since November 2007 with an energy threshold of a few 100s of GeV, is observing the Moon shadow with high statistical significance. Using about 1 year data, an upper limit of the proton/antiproton flux ratio in the few-TeV energy region is set to a few percent with a confidence level of 90%.

Cosmic ray antiprotons provide an important probe to study the cosmic ray propagation in the interstellar space and to investigate the existence of dark matter. Acting the Earth-Moon system as a magnetic spectrometer, paths of primary antiprotons are deflected in the opposite sense with respect to those of the protons in their way to the Earth. This effect allows, in principle, the search for antiparticles in the direction opposite to the observed deficit of cosmic rays due to the Moon (the so-called `Moon shadow'). The ARGO-YBJ experiment, located at the Yangbajing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm2), is particularly effective in measuring the cosmic ray antimatter content via the observation of the cosmic rays shadowing effect due to: (1) good angular resolution, pointing accuracy and long-term stability; (2) low energy threshold; (3) real sensitivity to the geomagnetic field. Based on all the data recorded during the period from July 2006 through November 2009 and on a full Monte Carlo simulation, we searched for the existence of the shadow cast by antiprotons in the TeV energy region. No evidence of the existence of antiprotons is found in this energy region. Upper limits to the [`p]/p flux ratio are set to 5% at a median energy of 1.4 TeV and 6% at 5 TeV with a confidence level of 90%. In the TeV energy range these limits are the lowest available.

We studied the radiative muon decay μ+→e+νν¯γ by using for the first time an almost fully polarized muon source. We identified a large sample (∼13,000) of these decays in a total sample of 1.8×1014 positive muon decays collected in the MEG experiment in the years 2009–2010 and measured the branching ratio B(μ→eνν¯γ)=(6.03±0.14(stat.)±0.53(sys.))×10−8 for Ee>45 MeV and Eγ>40 MeV, consistent with the Standard Model prediction. The precise measurement of this decay mode provides a basic tool for the timing calibration, a normalization channel, and a strong quality check of the complete MEG experiment in the search for μ+→e+γ process.

Measuring the anisotropy of the arrival direction distribution of cosmic rays provides important information on the propagation mechanisms and the identification of their sources. In fact, the flux of cosmic rays is thought to be dependent on the arrival direction only due to the presence of nearby cosmic ray sources or particular magnetic-field structures. Recently, the observation of unexpected excesses at TeV energy down to an angular scale as narrow as 10° raised the possibility that the problem of the origin of Galactic cosmic rays may be addressed by studying the anisotropy. The ARGO-YBJ experiment is a full-coverage extensive air showers array, sensitive to cosmic rays with the energy threshold of a few hundred GeV. Searching for small-size deviations from the isotropy, the ARGO-YBJ Collaboration explored the declination region 20°–80°, making use of about 3.7x10**11 events collected from November 2007 to May 2012. In this paper, the detection of different significant (up to 13 standard deviations) medium-scale anisotropy regions in the arrival directions of cosmic rays is reported. The observation was performed with unprecedented detail. The relative excess intensity with respect to the isotropic flux extends up to 10**-3. The maximum excess occurs for proton energies of 10–20 TeV, suggesting the presence of unknown features of the magnetic fields the charged cosmic rays propagate through, or some contribution of nearby sources never considered so far. The observation of new weaker few-degree excesses throughout the sky region 195° < R.A. < 290° is reported for the first time.

The MEG experiment makes use of one of the world’s most intense low energy muon beams, in order to search for the lepton flavour violating process μ+→e+γ. We determined the residual beam polarization at the thin stopping target, by measuring the asymmetry of the angular distribution of Michel decay positrons as a function of energy. The initial muon beam polarization at the production is predicted to be Pμ=−1 by the Standard Model (SM) with massless neutrinos. We estimated our residual muon polarization to be Pμ=−0.86±0.02 (stat) +0.05−0.06 (syst) at the stopping target, which is consistent with the SM predictions when the depolarizing effects occurring during the muon production, propagation and moderation in the target are taken into account. The knowledge of beam polarization is of fundamental importance in order to model the background of our μ+→e+γ search induced by the muon radiative decay: μ+→e+ν¯μνeγ.

We report a design of photocathode, which combines the good photoemissive properties of lead (Pb) and the advantages of superconducting performance of niobium (Nb) when installed into a superconducting radio-frequency gun. The new configuration is obtained by a coating of Nb thin film grown on a disk of Pb via pulsed laser deposition. The central emitting area of Pb is masked by a shield to avoid the Nb deposition. The nanomechanical properties of the Nb film, obtained through nanoindentation measurements, reveal a hardness of 2.8±0.3 GPa, while the study of the electrical resistivity of the film shows the appearance of the superconducting transitions at 9.3 K and 7.3 K for Nb and Pb, respectively, very close to the bulk material values. Additionally, morphological, structural and contamination studies of Nb thin film expose a very low droplet density on the substrate surface, a small polycrystalline orientation of the films and a low contamination level. These results, together with the acceptable Pb quantum efficiency of 2×10−5 found at 266 nm, demonstrate the potentiality of the new concept photocathode.

We propose a new photocathode configuration which presents the quantum efficiency and work function of yttrium (Y) and at the same time preserves all of the advantages of copper (Cu) when inserted into a radio-frequency gun. The configuration consists of a disk of Y covered by a coating of Cu deposited using the pulsed laser ablation technique, while masking the central part of the Y disk by a shield making the photoemission directly from the Y bulk possible. The new device was characterised by scanning electron microscopy to deduce the morphology and by X-ray diffraction to obtain structure information on both Cu film and Y substrate. The electrical resistivity of the Cu film was also measured obtaining a value slightly greater than that of bulk high purity

The analysis of a combined data set, totaling 3.6 × 10(14) stopped muons on target, in the search for the lepton flavor violating decay μ(+) → e(+)γ is presented. The data collected by the MEG experiment at the Paul Scherrer Institut show no excess of events compared to background expectations and yield a new upper limit on the branching ratio of this decay of 5.7 × 10(-13) (90% confidence level). This represents a four times more stringent limit than the previous world best limit set by MEG.

We present a new result based on an analysis of the data collected by the MEG detector at the Paul Scherrer Institut in 2009 and 2010, in search of the lepton-flavor-violating decay μ→eγ. The likelihood analysis of the combined data sample, which corresponds to a total of 1.8×10^14 muon decays, gives a 90% C.L. upper limit of 2.4×10^-12 on the branching ratio of the μ→eγ decay, constituting the most stringent limit on the existence of this decay to date.

The Forbush decrease following the large X2 solar flare on mid-February 2011 has been observed by the muon telescopes of the EEE Project, which are located in several Italian sites and at CERN. Data from two different telescopes of the EEE network have been analyzed and compared to those measured by neutron monitor stations. The variation of the muon counting rate during the Forbush decrease was also extracted for different intervals of the azimuthal angle of the incoming muons.

We report the observation of TeV γ-rays from the Cygnus region using the ARGO-YBJ data collected from 2007 November to 2011 August. Several TeV sources are located in this region including the two bright extended MGRO J2019+37 and MGRO J2031+41. According to the Milagro data set, at 20 TeV MGRO J2019+37 is the most significant source apart from the Crab Nebula. No signal from MGRO J2019+37 is detected by the ARGO-YBJ experiment, and the derived flux upper limits at the 90% confidence level for all the events above 600 GeV with medium energy of 3 TeV are lower than the Milagro flux, implying that the source might be variable and hard to be identified as a pulsar wind nebula. The only statistically significant (6.4 standard deviations) γ-ray signal is found from MGRO J2031+41, with a flux consistent with the measurement by Milagro.

The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 2007, has been observed for ∼4 years by the ARGO-YBJ experiment at TeV energies, with a statistical significance of 6.2 standard deviations. The peak of the signal is found at a position consistent with the pulsar PSR J1907+0602. Parameterizing the source shape with a two-dimensional Gauss function, we estimate an extension of σext = 0.49° ± 0.22°, which is consistent with a previous measurement by the Cherenkov Array H.E.S.S. The observed energy spectrum is dN/dE = (6.1 ± 1.4) × 10−13 (E/4 TeV)**(−2.54±0.36) photons cm−2 s−1 TeV−1, in the energy range of ∼1–20 TeV. The measured gamma-ray flux is consistent with the results of the Milagro detector, but is ∼2–3 times larger than the flux previously derived by H.E.S.S. at energies of a few TeV. The continuity of the Milagro and ARGO-YBJ observations and the stable excess rate observed by ARGO-YBJ and recorded in four years of data support the identification of MGRO J1908+06 as the steady powerful TeV pulsar wind nebula of PSR J1907+0602, with an integrated luminosity over 1 TeV ∼ 1.8 times the luminosity of the Crab Nebula.

We report the observation of a very high energy gamma-ray source whose position is coincident with HESS J1841−055. This source has been observed for 4.5 years by the ARGO-YBJ experiment from 2007 November to 2012 July. Its emission is detected with a statistical significance of 5.3 standard deviations. Parameterizing the source shape with a two-dimensional Gaussian function, we estimate an extension σ = (0.40+0.32−0.22)°, which is consistent with the HESS measurement. The observed energy spectrum is dN/dE=(9.0±1.6)×10**(−13) (E/5 TeV)**(− 2.32±0.23) photons cm−2 s−1 TeV−1, in the energy range 0.9–50 TeV. The integral gamma-ray flux above 1 TeV is 1.3±0.4 Crab, which is 3.2±1.0 times the flux derived by HESS. The differences in the flux determination between HESS and ARGO-YBJ and possible counterparts at other wavelengths are discussed.

Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important tool to determine the performance of an air shower array. Indeed, the westward displacement of the shadow center, due to the bending effect of the geomagnetic field on the propagation of cosmic rays, allows the setting of the absolute rigidity scale of the primary particles inducing the showers recorded by the detector. In addition, the shape of the shadow permits to determine the detector point spread function, while the position of the deficit at high energies allows the evaluation of its absolute pointing accuracy. In this paper we present the observation of the cosmic ray Moon shadowing effect carried out by the ARGO-YBJ experiment in the multi-TeV energy region with high statistical significance (55 standard deviations). By means of an accurate Monte Carlo simulation of the cosmic rays propagation in the Earth-Moon system, we have studied separately the effect of the geomagnetic field and of the detector point spread function on the observed shadow. The angular resolution as a function of the particle multiplicity and the pointing accuracy have been obtained. The primary energy of detected showers has been estimated by measuring the westward displacement as a function of the particle multiplicity, thus calibrating the relation between shower size and cosmic ray energy. The stability of the detector on a monthly basis has been checked by monitoring the position and the deficit of the Moon shadow. Finally, we have studied with high statistical accuracy the shadowing effect in the day/’’night’’ time looking for possible effect induced by the solar wind.

The EEE (Extreme Energy Events) Project is an experiment for the detection of cosmic ray muons by means of a sparse array of telescopes, each made of three Multigap Resistive Plate Chambers (MRPC), distributed over all the Italian territory and at CERN. The main scientific goals of the Project are the investigation of the properties of the local muon flux, the detection of Extensive Air Showers (EAS) and the search for long-distance correlations between far telescopes. The Project is also characterized by a strong educational and outreach aspect since the telescopes are managed by teams of students and teachers who had previously constructed them at CERN. In this paper an overall description of the experiment is given, including the design, construction and performance of the telescopes. The operation of the whole array, which currently consists of more than 50 telescopes, is also presented by showing the most recent physics results.

The purpose of this paper is to present a project in order to verify -without the need of knowing the distance CERN-Gran Sasso- the discovery made by the OPERA Collaboration concerning the speed of the CERN neutrinos. The project consists of two parts. A simple one and a less simple one. Both have the great advantage of being totally independent of the knowledge of the distance, ≃ 732 km, between the two Labs, CERN and LNGS, where the neutrinos are produced and detected, respectively. The "simple" version of this project is based on the high-energy horizontal cosmic muons, which traverse LVD and OPERA detectors, thus allowing to cross-calibrate the timing systems of both experiments in a way which is totally independent of the TOF measurements of CNGS. This component of the project is being studied in collaboration with the OPERA group, as the time stabilities of both experiments are needed. In fact it is since a long time that the two groups are engaged with this problem. In this paper we will present and discuss the "less simple" part which allows to establish, at the highest possible level of accuracy, if (v > c) effects really exist.

The ARGO-YBJ experiment is an air shower detector for gamma ray astronomy and cosmic ray studies with an energy threshold of ∼500 GeV. Working in "single particle mode", i.e. counting the single particles hitting the detector at fixed time intervals, ARGO-YBJ can monitor cosmic ray and gamma ray transients at energies of a few GeV. The single particle counting rate is modulated by the atmospheric pressure and temperature, and is affected by the local radioactivity from soil and air. Among the radioactive elements, radon gas is of particular importance since its concentration in air can vary significantly, according to environmental conditions. In this paper we evaluate the contribution of the radon daughter gamma ray emitters to the single particle counting rate measured by ARGO-YBJ. According to our analysis, the radon gas contribution is roughly 1-2%, producing a counting rate modulation of the same order of magnitude of the atmospheric effects.

The Extreme Energy Events (EEE) Project is devoted to the study of Extensive Atmospheric Showers through a network of muon telescopes, installed in High Schools, with the further aim of introducing young students to particle and astroparticle physics. Each telescope is a tracking detector composed of three Multi-gap Resistive Plate Chambers (MRPC) with an active area of 1.60 × 0.80 m^2. Their characteristics are similar to the ones built for the Time Of Flight array of the ALICE Experimentat LHC . The EEE Project started with a few pilot towns, where the telescopes have been taking data since 2008, and it has been constantly extended, reaching at present more than 50 MRPCs telescopes. They are spread across Italy with two additional stations at CERN, covering an area of around 3 × 105 km^2, with a total surface area for all the MRPCs of 190 m^2. A comprehensive description of the MRPCs network is reported here: efficiency, time and spatial resolution measured using cosmic rays hitting the telescopes. The most recent results on the detector and physics performance from a series of coordinated data acquisition periods are also presented.

The monitoring of galactic cosmic ray flux decreases is of interest for the understanding of phenomena that occur on the solar corona, as well as on other observable stars. As it is known, they are related to the emission of mass from the star corona and often related to solar flares, even if such relation is not completely understood. The effect on the solar wind directly affects the measured galactic cosmic ray flux on Earth, giving typical flux fluctuations of a few percent on a few days basis. The phenomenon is therefore observable by any apparatus surveying the cosmic ray radiation with a comparable overall accuracy. The Extreme Energy Events telescope array is an array of 47 tracing detector (growing), each made of three MRPC planes, spread over more than 10 degrees in latitude and 11 in longitude, organized in clusters and single telescope stations. The overall acceptance of the EEE stations allows for a flux rate measurement within the 15-50 particle/s, depending on the set-up, while the timing within different station is driven by the GPS time resolution and it is better than 50 ns. On November 10, 2015, a flux decrease was observed at the same time by six stations, covering almost the whole latitude and longitude range. Even if the s/n ratio by a single station was between 1 and 3, the averaged observation on the whole set of telescopes gave a s/n~4, better than what was obtained by OULU monitor. This observation came after other flux decreases observed by EEE. The observation is promising, in view of the construction of a solar surface phenomena survey, with both high accuracy and low systematics and wide longitude/latitude coverage features.

The full coverage extensive airshower detector ARGO-YBJ, located in Tibet at 4300 m of altitude, has monitored the sky at gamma ray energy E > 0.6 TeV in the declination band from -10° to +70°. In 424 days the Crab Nebula and Mrk421 have been detected with a significance, respectively, of 7.0 and 8.0 standard deviations. The analysis of the cosmic ray background in the same sky band, has revealed the existence of a significant excess of the cosmic ray flux in two localized regions of angular size 10°–30°, confirming previous indications. The origin of such excesses is still unexplained. During 2008 the observed Mrk421 flux was highly variable, with the strongest flares in March–June, in good correlation with X-ray data. One of the most intense flares occurred in the first half of June and has been deeply studied by different detectors in the energy range from optical to 100MeV gamma rays, but only partially up to TeV energies, since the moon lighth ampered the Cherenkov telescope measurements during the second and most intense part of the emission. Our data complete these observations, with the detection of a signal of intensity of about 7 Crab units on June 11–13, with a statistical significance of 4.2 standard deviations. The observed flux is consistent with a prediction made in the frame work of the Synchrotron Self-Compton model, in which the flare is caused by a rapid acceleration of leptons in the jet.

The Extreme Energy Events (EEE) project, a cosmic ray physics experiment, is at the sametime an excellent outreach project. Its scientific goal is the study of extended air showers from high energy cosmic rays and extreme energy events by detecting the muon component of the shower. To this aim, a network of muon telescopes has been installed in high schools distributed all over Italy; each telescope consists of three planes of Multigap Resistive Plate Chambers which allow the reconstruction of the muon direction. The search for extended air showers is based on the search for coincidences between telescopes. The project was conceived by Prof. A. Zichichi in order to interest high school students in science and give them a hands-on experience of scientific research

The Extreme Energy Events (EEE) project aims to study extended air showers from high energy cosmic rays and extreme energy events by detecting the muon component of the shower. To achieve this goal, a network of muon telescopes has been installed in high schools distributed all over Italy. Each muon telescope consists of three large area (80 × 160 cm2) Multigap Resistive Plate Chambers (MRPCs). Each MRPC has 24 pickup strips read out at both ends; the hit position along the strip is thus deduced from the time difference. This design offers pointing capability, so that the muon direction can be reconstructed. The project has been conceived by Prof. A. Zichichi in order to rekindle the interest of young people in science and give them a first-hand experience of scientific research.

The search for gamma-ray burst (GRB) emission in the energy range of 1-100 GeV in coincidence with the satellite detection has been carried out using the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) experiment. The high-altitude location (4300 m a.s.l.), the large active surface (~6700 m2 of Resistive Plate Chambers), the wide field of view (~2 sr, limited only by the atmospheric absorption), and the high duty cycle (>86%) make the ARGO-YBJ experiment particularly suitable to detect short and unexpected events like GRBs. With the scaler mode technique, i.e., counting all the particles hitting the detector with no measurement of the primary energy and arrival direction, the minimum threshold of ~1 GeV can be reached, overlapping the direct measurements carried out by satellites. During the experiment lifetime from 2004 December 17 to 2013 February 7, a total of 206 GRBs occurring within the ARGO-YBJ field of view (zenith angle θ ≤ 45°) have been analyzed. This is the largest sample of GRBs investigated with a ground-based detector. Two light curve models have been assumed and since in both cases no significant excess has been found, the corresponding fluence upper limits in the 1-100 GeV energy region have been derived, with values as low as 10–5 erg cm–2. The analysis of a subset of 24 GRBs with known redshift has been used to constrain the fluence extrapolation to the GeV region together with possible cutoffs under different assumptions on the spectrum.

A search for long distance correlations between individual Extensive Air Showers (EAS) detected by pairs of MRPC telescopes of the Extreme Energy Events (EEE) network was carried out. The search for an anomaly in these events is the purpose of our work. A dataset obtained by all the possible 45 pairs between 10 EEE cluster sites (hosting at least two telescopes), located at relative distances between 86 and 1200km, was analyzed, corresponding to an overall period of 3968 days time exposure. To estimate the possible event excess with respect to the spurious rate, the number of coincidence events was extracted as a function of the time difference between the arrival of the showers in the two sites, from +/-10s to the smallest time interval where events are still observed. The analysis was done taking into account both the time and orientation correlation between the showers detected by the telescope pairs. A few candidate events with unusually small time difference and angular distance were observed, with a p-value sensibly smaller than a confidence level of 0.05.

The final results of the search for the lepton flavour violating decay μ^+ → e^+ γ based on the full dataset collected by the MEG experiment at the Paul Scherrer Institut in the period 2009–2013 and totalling 7.5x10^14 stopped muons on target are presented. No significant excess of events is observed in the dataset with respect to the expected background and a new upper limit on the branching ratio of this decay of B(μ^+ → e^+ γ)<4.2x10^-13 (90 % confidence level) is established, which represents the most stringent limit on the existence of this decay to date.

Drift chambers operated with helium-based gas mixtures represent a common solution for tracking charged particles keeping the material budget in the sensitive volume to a minimum. The drawback of this solution is the worsening of the spatial resolution due to primary ionisation fluctuations, which is a limiting factor for high granularity drift chambers like the MEG II tracker. We report on the measurements performed on three different prototypes of the MEG II drift chamber aimed at determining the achievable single-hit resolution. The prototypes were operated with helium/isobutane gas mixtures and exposed to cosmic rays, electron beams and radioactive sources. Direct measurements of the single hit resolution performed with an external tracker returned a value of 110 μm, consistent with the values obtained with indirect measurements performed with the other prototypes.

The events recorded by ARGO-YBJ in more than five years of data collection have been analyzed to determine the diffuse gamma-ray emission in the Galactic plane at Galactic longitudes 25° < l < 100° and Galactic latitudes ∣ b | < 5°. The energy range covered by this analysis, from ∼350 GeV to ∼2 TeV, allows the connection of the region explored by Fermi with the multi-TeV measurements carried out by Milagro. Our analysis has been focused on two selected regions of the Galactic plane, i.e., 40° < l < 100° and 65° < l < 85° (the Cygnus region), where Milagro observed an excess with respect to the predictions of current models. Great care has been taken in order to mask the most intense gamma-ray sources, including the TeV counterpart of the Cygnus cocoon recently identified by ARGO-YBJ, and to remove residual contributions. The ARGO-YBJ results do not show any excess at sub-TeV energies corresponding to the excess found by Milagro, and are consistent with the predictions of the Fermi model for the diffuse Galactic emission. From the measured energy distribution we derive spectral indices and the differential flux at 1 TeV of the diffuse gamma-ray emission in the sky regions investigated.

The Astrophysical Radiation with Ground-based Observatory at Yang Ba Jing (ARGO-YBJ) detector is an extensive air shower array that has been used to monitor the northern γ-ray sky at energies above 0.3 TeV from 2007 November to 2013 January. In this paper, we present the results of a sky survey in the declination band from −10◦ to 70◦, using data recorded over the past five years. With an integrated sensitivity ranging from 0.24 to ∼1 Crab units depending on the declination, six sources have been detected with a statistical significance greater than five standard deviations. Several excesses are also reported as potential γ-ray emitters. The features of each source are presented and discussed. Additionally, 95% confidence level upper limits of the flux from the investigated sky region are shown. Specific upper limits for 663 GeV γ-ray active galactic nuclei inside the ARGO-YBJ field of view are reported. The effect of the absorption of γ-rays due to the interaction with extragalactic background light is estimated.

The ARGO-YBJ experiment has been in stable data taking from November 2007 till February 2013 at the YangBaJing Cosmic Ray Observatory (4300 m a.s.l.). The detector consists of a single layer of Resistive Plate Chambers (RPCs) (6700 m2) operated in streamer mode. The signal pick-up is obtained by means of strips facing one side of the gas volume. The digital readout of the signals, while allows a high space–time resolution in the shower front reconstruction, limits the measurable energy to a few hundred TeV. In order to fully investigate the 1–10 PeV region, an analog readout has been implemented by instrumenting each RPC with two large size electrodes facing the other side of the gas volume. Since December 2009 the RPC charge readout has been in operation on the entire central carpet (5800 m2). In this configuration the detector is able to measure the particle density at the core position where it ranges from tens to many thousands of particles per m2. Thus ARGO-YBJ provides a highly detailed image of the charge component at the core of air showers. In this paper we describe the analog readout of RPCs in ARGO-YBJ and discuss both the performance of the system and the physical impact on the EAS measurements.

Gamma ray source detection above 30TeV is an encouraging approach for finding galactic cosmic ray origins. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100 GeV. To target the goals, the ARGO-YBJ experiment has been established. Significant progresses have been made in the experiment. A large air shower detector array in an area of 1 km2 is proposed to boost the sensitivity. Hybrid detections with multitechniques will allow a good discrimination between different types of primary particles, including photons and protons, thus enable an energy spectrum measurement for individual species. Fluorescence light detector array will extend the spectrum measurement to 100 PeV and higher where the second knee is located. An energy scale determined by balloon experiments at 10 TeV will be propagated to ultra high energy cosmic ray experiments.

The ARGO-YBJ experiment is an Extensive Air Shower (EAS) array which combines high altitude location and full coverage active area in order to reach low energy threshold at a level of few hundred of GeV. The large field of view (≈ 2 sr) and the high duty cycle (≥ 90%) allow the continuous monitoring of the sky searching for unknown sources and unpredictable events, such as flares in blazar emissions and high energy Gamma-Ray Bursts (GRBs). In this paper I will briefly report on the detector performance and on some preliminary results achieved in γ-ray astronomy.

The ARGO-YBJ experiment is in stable data taking since November 2007 at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R.China, 4300 m a.s.l.). It exploits a full coverage and high altitude approach to the small air showers detection. The detector is made of a single layer of RPCs operated in streamer mode, fully instrumenting a central carpet of about 5700 m2, then a guard ring extends the partially instrumented area to about 11,000 m2. The large field of view (∼ 2 sr) and the high duty cycle (≥ 85%) allow a continuous monitoring of the sky in the declination band from -10° to 70°; the detector operates with an energy threshold of a few hundred GeV. Recent achieved results will be reported.

A Drift Chamber is a detector used in high energy physics experiments for determining charged particles trajectories. The signal pulses from all the wires are then collected and the particle trajectory is tracked assuming that the distances of closest approach (the impact parameter) between the particle trajectory and the wires coincide with the distance between the cluster ions generated by the particle and the wire closer to it. The widespread use of helium based gas mixtures, which produces a low ionization clusters density (12 cluster/cm in a 90/10 helium/iso-butane mixture), introduces a sensible bias in the impact parameter assumption, particularly for short impact parameters and small cell drift chambers. Recently, an alternative track reconstruction (Cluster Counting/Timing) technique has been proposed, which consists in measuring the arrival times on the wires of each individual ionization cluster and combining these times to get a bias free estimate of the impact parameter. However, in order to efficiently exploiting the cluster timing technique, it is necessary to have read-out interfaces capable of processing a large quantity of high speed signals. We describe the design of a read-out board capable of acquiring the information coming from a fast digitization of the signals generated in a drift chamber and the algorithm for identifying the individual ionization pulse peaks and recording their time and amplitude.

The MEG experiment searches for the charged lepton flavor violating decay, μ +→ e+γ. MEG has already determined the world best upper limit on the branching ratio BR<4.2× 10−13 at 90% CL. An upgrade of the whole detector has been approved to obtain a substantial increase in sensitivity. Currently MEG is in upgrade phases, this phase involves all the detectors. The new positron tracker is a single volume, full stereo, small cells drift chamber (DCH) co-axial to the beam line. It is composed of 10 concentric layers and each single drift cell is approximately square 7 mm side, with a 20 μ m gold plated W sense wire surrounded by 40 μ m and 50 μ m silver plated Al field wires in a ratio of 5:1, about 12,000 wires. Due to the high wire density (12 wires/cm2), the use of the classical feed-through technique as wire anchoring system could hardly be implemented and therefore it was necessary to develop new wiring strategies. The number of wires and the stringent requirements on the precision of their position and on the uniformity of the wire mechanical tension impose the use of an automatic system to operate the wiring procedures. This wiring robot, designed and built at the INFN Lecce and University of Salento laboratories, consists of: ⋅ a semiautomatic wiring machine with a high precision on wire mechanical tensioning (better than 0.5 g) and on wire positioning (20 μ m) for simultaneous wiring of multiwire layers; ⋅ a contact-less infrared laser soldering tool; ⋅ an automatic handling system for storing and transporting the multi-wire layers. The drift chamber is currently under construction at INFN and should be completed by the end of summer 2017 to be then delivered to PSI for commissioning.

CORAM (COsmic RAy Mission) is an outreach program carried out by INFN and the University of Salento in close collaboration with high schools. Students and their teachers are involved in the design, construction, test and operation of detectors for the measurement of several properties of the cosmic ray flux. The results of a set of measurements, made with a first detector prototype at different altitudes and underground, will be described.

On the occasion of the forthcoming centenary of the cosmic ray radiation discovery, a group of researchers from Lecce Physics Department and INFN proposed to repeat an experiment similar to the one performed by Victor Hess in 1912 for outreach and educational purposes. Several High School students are involved in this activity, named CORAM (Cosmic RAy Mission), that provides the design, construction and test of a detector for the measurement of the cosmic ray flux as a function of the atmospheric altitude. The detector is made by scintillator layers readout by APDs (Avalanche Photo Diode) interposed with appropriate absorber layers and put into coincidence. The experiment will be hosted on an atmospheric balloon from the Italian space agency (ASI Agenzia Spaziale Italiana) that presumably will take off in the summer of 2012. The INFN encouraged and supported this outreach activity by funding the detector and Data Acquisition System (DAQ).

CORAM (COsmic RAy Mission) is an experiment carried out by INFN and the University of Salento for studying and measuring several properties of the cosmic ray flux. The CORAM detector can be used both for experimental and outreach goals and it is designed also for aereospace applications. The final Data Acquisition system (DAQ) has been implemented in order to create a compact, redundant and user friendly device that can be used for several purposes. In this work we present this DAQ system and the electronics used.

The Extreme Energy Events Project is an experiment for the detection of Extensive Air Showers which exploits the Multigap Resistive Plate Chamber technology. At the moment 40 EEE muon telescopes, distributed all over the Italian territory, are taking data, allowing the relative analysis to produce the first interesting results, which are reported here. Moreover, this Project has a strong added value thanks to its effectiveness in terms of scientific communication, which derives from the peculiar way it was planned and carried on

The Extreme Energy Events (EEE) project is an extended array for cosmic rays survey. It was conceived by Antonino Zichichi and supported by the Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi” with the collaboration of the European Organization for Nuclear Research (CERN), of the Istituto Nazionale di Fisica Nucleare (INFN) and of the Italian Ministry of Education, University and Research (MIUR). This experiment is aimed to study cosmic rays of extreme high energy, and related phenomena. To achieve this goal, a network of nearly 50 muon telescopes has been installed in high schools, distributed throughout the Italian territory, either as single stations or clusters. During the second coordinated run of data taking, which ended in May 2016, 25 billion muon tracks were detected and reconstructed. This huge amount of data, allows us to undertake various studies: the dependence of the local muon flux on solar activity; the sky anisotropy on sub-TeV scale; event correlations, due to EAS, between clustered telescopes at distances from a few hundred meters to over a kilometre. The status of the project and some results will be presented.

The Extreme Energy Events (EEE) Project is meant to be the most extensive experiment to detect secondary cosmic particles in Italy. To this aim, more than 50 telescopes have been built at CERN and installed in high schools distributed all over the Italian territory. Each EEE telescope comprises three large area Multigap Resistive Plate Chambers (MRPCs) and is capable of reconstructing the trajectories of the charged particles traversing it with a good angular resolution. The excellent performance of the EEE telescopes allows a large variety of studies, from measuring the local muon flux in a single telescope, to detecting extensive air showers producing time correlations in the same metropolitan area, to searching for large-scale correlations between showers detected in telescopes tens, hundreds or thousands of kilometers apart. In addition to its scientific goal, the EEE Project also has an educational and outreach objective, its aim being to motivate young people by involving them directly in a real experiment. High school students and teachers are involved in the construction, testing and start-up of the EEE telescope in their school, then in its maintenance and data-acquisition, and later in the analysis of the data. During the last couple of years a great boost has been given to the EEE Project through the organization of simultaneous and centralized data taking with the whole telescope array. The raw data from all telescopes are transferred to CNAF (Bologna), where they are reconstructed and stored. The data are currently being analyzed, looking at various topics: variation of the rate of cosmic muons with time, upward going muons, muon lifetime, search for anisotropies in the muon angular distribution and for time coincidences between stations. In this paper an overall description of the experiment is given, including the design, construction and performance of the telescopes. The operation of the whole array is also presented by showing the most recent physics results.

The Extreme Energy Events Project has been designed to join the scientific interest of a cosmic rays physics experiment with the enormous didactic potentiality deriving from letting it be carried out by high school students and teachers. After the initial phase, the experiment is starting to take data continuously, and the first interesting physics results have been obtained, demonstrating the validity of the idea of running a real physics investigation in these peculiar conditions. Here an overview of its structure and status is presented, together with some studies about detector performance and first physics results.

The Extreme Energy Events project has been conceived to join the scientific interest of a real cosmic rays physics experiment with the enormous didactic potentiality deriving from letting it be carried out by high school students and teachers. After the initial phase, the experiment is starting to take data continuously, and the first interesting physics results have been obtained, demonstrating the validity of the idea of running a real physics investigation in these peculiar conditions. In this paper an overview of its structure and status is presented; also few results obtained at the sites are included.

The MEG (Mu to Electron Gamma) experiment has been running at the Paul Scherrer Institut (PSI), Switzerland since 2008 to search for the decay μ +→e+ γ by using one of the most intense continuous μ + beams in the world. This paper presents the MEG components: the positron spectrometer, including a thin target, a superconducting magnet, a set of drift chambers for measuring the muon decay vertex and the positron momentum, a timing counter for measuring the positron time, and a liquid xenon detector for measuring the photon energy, position and time. The trigger system, the read-out electronics and the data acquisition system are also presented in detail. The paper is completed with a description of the equipment and techniques developed for the calibration in time and energy and the simulation of the whole apparatus.

In this chapter we describe the design of a Field Programmable Gate Array (FPGA) board capable of acquiring the information coming from a fast digitization of the signals generated in a drift chambers. The digitized signals are analyzed using an ad hoc real time algorithm implemented in the FPGA in order to reduce the data throughput coming from the particle detector.

Time correlated events due to cosmic muons from extensive air showers have been detected by means of telescope pairs of the EEE (Extreme Energy Events) Project array. The coincidence rate, properly normalized for detector acceptance, efficiency and altitude location, has been extracted as a function of the relative distance between the telescopes. The results have been also compared with additional measurements carried out by small scintillator detectors at various distances

We present results on the measurements of gas gain for gas mixtures at absolute pressure below the atmospheric pressure, down to 100 mbar, and their relative stability. Besides the obvious advantage of further limiting the contribution to the momentum measurement due to multiple scattering, the operation at low pressure allows for a fine tuning of the working parameters of a drift chamber like drift velocity, diffusion and specific ionization. Furthermore, such a possibility is of particular interest for experiments like the direct muon to electron conversion experiment Mu2e at Fermilab, where the tracking detector needs to operate in vacuum. Plans for extending the measurements to transport parameters, like drift velocity and diffusion, will also be presented.

Multigap Resistive Plate Chambers (MRPCs) are gas detectors operating in avalanche saturated mode at a standard voltage ranges around 18 ÷ 20 kV, applied by means of DC Low Voltage to DC High Voltage converters (DC/DC converters). This device is used in the Extreme Energy Events Project (EEE Project), an innovative experiment to study high energy cosmic rays by using a network of tracking detectors, located across the Italian territory plus CERN, over a total area of 105 km2. Each EEE telescope is composed of three MRPCs. A suitable device to supply and control voltage and current for the DC-DC converters and for the MRPCs front-end cards has been developed. This electronic module is interfaced with the DAQ computer, controlled by a dedicated software in LabVIEW and, since computer is permanently online, the LV/HV system can be continuously monitored from remote.