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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

We present a novel low mass drift chamber concept, developed in order to fulfill the stringent requirements imposed by the experiments for extremely rare processes, which require high resolutions (order of 100–200 keV/c) for particle momenta in a range (50–100 MeV/c) totally dominated by the multiple scattering contribution. We describe a geometry optimization procedure and a new wiring strategy with a feed-through-less wire anchoring system developed and tested on a drift chamber prototype under completion at INFN- Lecce .