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Abstract: OPERA is a dedicated experiment for the observation of into oscillations through appearance using a 730km long baseline beam from CERN to the Gran Sasso underground laboratory. The detector is equipped with two spectrometers for muon identification and charm background rejection. Bakelite RPCs are used as inner trackers inside the iron magnet of the spectrometers. The experiment has already performed two short runs in 2006 and 2007. Results about the RPC performances are presented. [Copyright &y& Elsevier]

The OPERA experiment foresees the use of about of RPCs, that will be tested before the installation in a dedicated cosmic ray test facility. The test facility is composed of 2 triggering walls selecting horizontal cosmic rays muons. Each wall houses 64 glass RPCs equipped with 128 horizontal Flat Cable Strips. The z-coordinate is measured with a standard digital chain, while the x-coordinate is obtained by measuring the propagation time of the signals along the strips. In this paper the performance of the trigger walls and the first results of the RPC debug are presented. [Copyright &y& Elsevier]

Before the installation in the OPERA experiment, bakelite Resistive Plate Chambers are subjected to a chain of quality tests performed at the Gran Sasso Laboratories. Mechanical properties are first investigated in a fully automatized station, measuring the gas leakage and checking the gluing of the internal spacers. Then electrical properties are tested: current vs. voltage characteristics are measured both with pure argon and with gas mixture filling; moreover the short term behavior of the current is monitored. Finally the response uniformity is tested, measuring the efficiency on the entire detector surface at cosmic rays fluxes. In this paper we present the test chain and the results on a large set of chambers. [Copyright &y& Elsevier]

OPERA is one of the two detectors foreseen in the CERN Neutrino to Gran Sasso project, devoted to the detection of into oscillations in the parameter region suggested by SuperKamiokande data on atmospheric neutrinos. Bakelite RPCs will be used to instrument the iron yoke of the muon spectrometers. We present the results of long-term (greater than 6 months) streamer operations of real size OPERA RPCs at cosmic rays fluxes. Given the very low rate observed in the underground Gran Sasso Laboratories, under 3km w.e., even this short time period is equivalent to more than 10 OPERA years. Results of tests with different gas mixtures are reported, in view of decreasing the streamer charge of operation for the RPCs employed in the experiment. [Copyright &y& Elsevier]

In the framework of the study for a large magnetic detector suitable for the physics at a neutrino factory, the data collected with the MONOLITH prototype at the T7-PS facility at CERN has been analyzed. The hadron shower angular resolution for pions followed a 10.4/√ of E(GeV)+10.1/E law for orthogonally incident particles. For a baseline of 732 km, this performance would allow the rejection of wrong sign muon background at the level of 10−6, and a capability to measure sin θ13 down to 10−3. A preliminary analysis of about 106 downward going muons collected at LNGS is also presented. The readout system upgrade allowed the monitoring of each glass RPC with a granularity of 1 cm2. [Copyright &y& Elsevier]

Several measurements have been made on different phototubes in order to select the type to be used for the readout system of the NOE magnetized scintillating fiber calorimeter. Characteristics such as gain, linearity, time resolution and cathode uniformity have been examined on several PMT types with standard, fine mesh or channel multiplier structure. The PMT response in the presence of the magnetized calorimeter fringe fields has also been studied. Here we report on the results of these measurements and of the comparisons between the different PMT types. [Copyright &y& Elsevier]

We present an overview of the data acquisition system (DAQ) and event building of OPERA. OPERA is a long baseline neutrino experiment with a high modularity detector and low event rate. To deal with these features a distributed DAQ system base on Ethernet standards for the data transfer has been chosen. A distributed GPS clock signal is used for synchronizations and time stamp of the data. This architecture allows very modular and flexible event building based on a software trigger strategy. We also present its specific application to the spectrometer sub-detector where RPC trackers are installed. Self-triggerability is a dedicated feature to be also sensitive to out-of-spill events and to possibly allow data taking before the official start of the experiment. [Copyright &y& Elsevier]

Abstract: OPERA is an experiment dedicated to the observation of into oscillations through appearance exploiting the CNGS beam. The experiment is composed by two identical super-modules, each with a target section (made of emulsion/lead bricks alternated with a scintillator Target Tracker) and a muon spectrometer (instrumented with bakelite RPCs and drift tubes). The RPCs are operated in streamer mode with the gas mixture Ar/C2H2F4/isoC4H10/SF6=75.4/20/4/0.6. The present performances of the RPC detectors are presented and the aging status of the system after four years of operation is described. The sample of events induced by the CNGS neutrino beam as well as a large sample of cosmic rays have also been used to study general properties of streamer-operated RPCs. [Copyright &y& Elsevier]