This paper describes the design and performance of a computer controlled emulsion Plate Changer for the automatic placement and removal of nuclear emulsion films for the European Scanning System microscopes. The Plate Changer is used for mass scanning and measurement of the emulsions of the OPERA neutrino oscillation experiment at the Gran Sasso lab on the CNGS neutrino beam. Unlike other systems it works with both dry and oil objectives. The film changing takes less than 20 s and the accuracy on the positioning of the emulsion films is about 10 mu m. The final accuracy in retrieving track coordinates after fiducial marks measurement is better than 1 mu m. (c) 2013 Elsevier B.V. All rights reserved.

The European Scanning System, developed to analyse nuclear emulsions at high speed, has been completed with the development of a high level software infrastructure to automate and support large-scale emulsion scanning. In one year, an average installation is capable of performing data-taking and online analysis on a total surface ranging from few m(2) to tens of m(2), acquiring many billions of tracks, corresponding to several TB. This paper focuses on the procedures that have been implemented and on their impact on physics measurements. The system proved robust, reliable, fault-tolerant and user-friendly, and seldom needs assistance. A dedicated relational Data Base system is the backbone of the whole infrastructure, storing data themselves and not only catalogues of data files, as in common practice, being a unique case in high-energy physics DAQ systems. The logical organisation of the system is described and a summary is given of the physics measurement that are readily available by automated processing. (C) 2012 Elsevier B.V. All rights reserved.

The purpose of this work is to report the measurement of a time-shift in the OPERA setup in a way totally independent of the Time-Of-Flight (TOF) measurements of CNGS neutrino events and without the need to know the distance between the two laboratories, CERN and LNGS, where the neutrinos are produced and detected, respectively. The LVD and OPERA experiments are both installed in the same laboratory: LNGS. The relative position of the two detectors, separated by an average distance of similar to 160 m, allows the use of very high-energy horizontal muons to cross-calibrate the timing systems of the two detectors, using a TOF technique, which, as stated above, is totally independent of the TOF of CNGS neutrino events. Indeed, the OPERA-LVD direction lies along the so-called "Teramo anomaly", a region in the Gran Sasso massif where LVD has established, many years ago, the existence of an anomaly in the mountain structure, which exhibits a low m.w.e. thickness for horizontal directions. The "abundant" high-energy horizontal muons (nearly 100 per year) going through LVD and OPERA exist because of this anomaly in the mountain orography. The total live time of the data in coincidence between the two experiments correspond to 1200 days from mid 2007 until March 2012. The time coincidence study of LVD and OPERA detectors is based on 306 cosmic-horizontal-muon events and shows the existence of a negative time-shift in the OPERA set-up of the order of Delta t(AB) = -(73 +/- 9) ns when two calendar periods, A and B, are compared. The first, A, goes from August 2007 to August 2008 plus the period from January 2012 to March 2012; the second period, B, goes from August 2008 to December 2011. This result shows a systematic effect in the OPERA timing system present from August 2008 until December 2011. The size of the effect, in terms of the cosmic horizontal muons TOF, is comparable with the neutrino velocity excess recently measured by OPERA. It is probably interesting not to forget that with the MRPC technology developed by the ALICE Bologna group the TOF world record accuracy of 20 ps was reached. This technology can be implemented at LNGS for a high-precision determination of TOF with the CNGS neutrino beams. If new experiments are needed for the study of neutrino velocities they must be able to detect effects an order of magnitude smaller than the value of the OPERA systematic effect.

The OPERA experiment is designed to search for nu(mu) -> nu(tau) oscillations in appearance mode, i.e., through the direct observation of the tau lepton in nu(tau)- charged current interactions. The experiment has taken data for five years, since 2008, with the CERN Neutrino to Gran Sasso beam. Previously, two nu(tau) candidates with a t decaying into hadrons were observed in a subsample of data of the 2008-2011 runs. Here we report the observation of a third nu(tau) candidate in the tau(-) -> mu(-) decay channel coming from the analysis of a subsample of the 2012 run. Taking into account the estimated background, the absence of nu(mu) -> nu(tau) oscillations is excluded at the 3.4 sigma level.

In spring 2012 CERN provided two weeks of a short bunch proton beam dedicated to the neutrino velocity measurement over a distance of 730 km. The OPERA neutrino experiment at the underground Gran Sasso Laboratory used an upgraded setup compared to the 2011 measurements, improving the measurement time accuracy. An independent timing system based on the Resistive Plate Chambers was exploited providing a time accuracy of similar to 1 ns. Neutrino and anti-neutrino contribution were separated using the information provided by the OPERA magnetic spectrometers. The new analysis profited from the precision geodesy measurements of the neutrino beaseline and of the CNGS/LNGS clock synchronization. The neutrino arrival time with respect to the one computed assuming the speed of light in vacuum is found to be delta t(nu) equivalent to TOFc - TOF nu = (0.6 +/- 0.4 (stat.)+/- 3.0 (syst.)) and delta t((nu) over bar) equivalent to TOFc-TOF(nu) over bar = (1.7 +/- 1.4 (stat.)+/- 3.1 (syst.)) ns for nu(mu) and (nu) over bar (mu), respectively. This corresponds to a limit on the muon neutrino velocity with respect to the speed of light of -1.8 x 10(-6) < (V-nu - c)/c < 2.3 x 10(-6) at 90% C.L. This new measurement confirms with higher accuracy the revised OPERA result.

The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km. The measurement is based on data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (6.5 +/- 7.4 (stat.)(-8.0)(+8.3)(sys.)) ns was measured corresponding to a relative difference of the muon neutrino velocity with respect to the speed of light (v - c)/c = (2.7 +/- 3.1 (stat.)(-3.3)(+1.34)(sys.)) x 10(-6). The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5 mu s long extractions, was confirmed by a test performed at the end of 2011 using a short bunch beam allowing to measure the neutrino time of flight at the single interaction level.

The OPERA detector, designed to search for nu(mu) -&gt; nu(tau) oscillations in the CNGS beam, is located in the underground Gran Sasso laboratory, a privileged location to study TeV-scale cosmic rays. For the analysis here presented, the detector was used to measure the atmospheric muon charge ratio in the TeV region. OPERA collected charge-separated cosmic ray data between 2008 and 2012. More than 3 million atmospheric muon events were detected and reconstructed, among which about 110000 multiple muon bundles. The charge ratio R-mu = N-mu+/N-mu- was measured separately for single and for multiple muon events. The analysis exploited the inversion of the magnet polarity which was performed on purpose during the 2012 Run. The combination of the two data sets with opposite magnet polarities allowed minimizing systematic uncertainties and reaching an accurate determination of the muon charge ratio. Data were fitted to obtain relevant parameters on the composition of primary cosmic rays and the associated kaon production in the forward fragmentation region. In the surface energy range 1-20 TeV investigated by OPERA, R-mu is well described by a parametric model including only pion and kaon contributions to themuon flux, showing no significant contribution of the prompt component. The energy independence supports the validity of Feynman scaling in the fragmentation region up to 200 TeV/nucleon primary energy.

A new method of momentum measurement of charged particles through multiple Coulomb scattering (MCS) in the OPERA lead-emulsion target is presented. It is based on precise measurements of track angular deviations carried out thanks to the very high resolution of nuclear emulsions. The algorithm has been tested with Monte Carlo pions. The results are found to

The OPERA experiment, designed to perform the first observation of nu(mu) -> nu(tau) oscillations in appearance mode through the detection of the tau leptons produced in nu(tau) charged current interactions, has collected data from 2008 to 2012. In the present paper, the procedure developed to detect tau particle decays, occurring over distances of the order of 1 mm from the neutrino interaction point, is described in detail and applied to the search for charmed hadrons, showing similar decay topologies as the tau lepton. In the analysed sample, 50 charm decay candidate events are observed while 54 +/- 4 are expected, proving that the detector performance and the analysis chain applied to neutrino events are well reproduced by the OPERA simulation and thus validating the methods for nu(tau) appearance detection.

The OPERA neutrino experiment in the underground Gran Sasso Laboratory (LNGS) was designed to perform the first detection of neutrino oscillations in direct appearance mode in the nu(mu) -&gt; nu(tau) channel, the nu(tau) signature being the identification of the tau-lepton created in its charged current interaction. The hybrid apparatus consists of a large mass emulsion film/lead target complemented by electronic detectors. Placed in the LNGS, it is exposed to the high-energy long-baseline CERN Neutrino beam to Gran Sasso (CNGS) 730 km away from the neutrino source. The observation of a first nu(tau) candidate event was reported in 2010. In this paper, we discuss the result of the analysis of the data taken during the first two years of operation (2008-2009) underlining the major improvements brought to the analysis chain and to the Monte Carlo simulations. The statistical significance of the one event observed so far is then evaluated to 95%.

The OPERA experiment is based on a hybrid technology combining electronic detectors (EDs) and nuclear emulsions. OPERA collected muon-neutrino interactions during the 2008 and 2009 physics runs of the CNGS neutrino beam, produced at CERN with an energy range of about 5-35 GeV. A total of 5.3x10(19) protons on target equivalent luminosity have been analysed with the OPERA EDs: scintillator strips target trackers and magnetic muon spectrometers equipped with resistive plate gas chambers and drift tubes, allowing a detailed reconstruction of muon-neutrino interactions. Charged current (CC) and neutral current (NC) interactions are identified, using the measurements in the EDs, and the NC/CC ratio is computed. The momentum distribution and the charge of the muon tracks produced in CC interactions are analysed. Calorimetric measurements of the visible energy are performed for both the CC and NC samples. For CC events, the Bjorken-y distribution and the hadronic shower profile are computed. The results are compared with a detailed Monte Carlo simulation of the response of EDs.