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Abstract: In this paper, we present the performance of the Neutron Zero Degree Calorimeter (ZN) for the ALICE experiment. The ZN is a quartz-fiber spaghetti calorimeter, which will measure the energy of the spectator neutrons in heavy ion collisions at the CERN LHC. Its principle of operation is based on the detection of the Cherenkov light produced by the charged particles of the shower in silica optical fibers, embedded in a W-alloy absorber. The detector was tested at CERN SPS using positive hadron and positron beams with momenta ranging from 50 to . The response of the calorimeter, the energy resolution, the localizing capability, the signal uniformity and the transverse profile of the detectable hadronic shower are presented. [Copyright &y& Elsevier]

Resistive Plate Chambers operated in streamer mode have been chosen as trigger detectors for the forward dimuon spectrometer of the ALICE experiment. During tests performed at CERN PS, small size prototypes with low-resistivity bakelite electrodes and with a strongly quenched gas mixture have shown the required rate capability, tracking and timing properties. Present efforts are devoted to the study of the detector performance after long irradiation periods. In this paper, a summary of the results of aging tests performed at the Gamma Irradiation Facility at CERN will be presented. Detectors show quite stable performance up to about , as the requirements for 10years operation program at LHC including a safety factor of 2. Afterwards, we observed an increase of the dark current not associated with an increase of the counting rate. We also report results of chemical analysis carried out by different CERN teams on exhaust gases and electrode surfaces of the detectors after aging. [Copyright &y& Elsevier]

The possibility to detect thermal neutrons with single gap resistive plate chambers (RPCs) has been investigated. The development of the detector has been performed in the frame of the detection and imaging of antipersonnel land-mine by neutron back-scattering (DIAMINE) European Project for humanitarian de-mining. The RPCs are simple devices widely used in many particles physics experiments as trigger detectors because of their fast response and good spatial resolution. The RPC detects the charged particles generated by neutrons via the (n,α) reaction on boron. A 10B4C thin coating on the inner surface of one RPC electrode is used as thermal neutron converter. A simulation study has been performed to optimize the converter thickness and the RPC working parameters. Tests on converter samples have been performed with a thermalized 252Cf source in order to evaluate the conversion efficiency. A first detector prototype has been realized and tested with cosmic rays and thermal neutrons. Results of simulation and experimental measurements of conversion efficiency, together with the description of the RPC prototype, are presented. [Copyright &y& Elsevier]

Presents a study which explored the performance of a forward neutron calorimeter for the ALICE experiment. Experimental set-up; Results; Discussion.

Abstract: The Zero Degree Calorimeters (ZDC) for the ALICE experiment will measure the energy of the spectator nucleons in heavy ion collisions at the CERN LHC, providing a direct measure of the centrality of the collisions. ZDC are spaghetti calorimeters, which detect the Cherenkov light produced by the shower particles in silica optical fibers embedded in a dense absorber. The main characteristics of the ZP and ZN detectors are described in this article. The calorimeters were tested at the CERN SPS using pion and electron beams with momenta ranging from 50 to . Test beam results such as the calorimeter response, the energy resolution, the signal uniformity and the localizing capability are presented. [Copyright &y& Elsevier]

The Zero Degree Calorimeters (ZDCs) for the ALICE experiment will measure the energy of the spectator nucleons in heavy ion collisions at the CERN LHC. The dipole magnets of the LHC beam optics will separate the ion beams from the spectator protons; the spectator protons and neutrons will be respectively detected by the proton (ZP) and the neutron (ZN) calorimeters. Since all the spectator nucleons have the same energy, the calorimeter response is proportional to their number, providing a direct information on the centrality of the collision. ZDCs are spaghetti calorimeters, which detect the Cherenkov light produced by the shower particles in silica optical fibers embedded in a dense absorber. The technical characteristics of ZP and ZN detectors are described. The calorimeters have been tested at the CERN SPS using pion and electron beams with momenta ranging from 50 to 200 GeV/c; the ZN detector behaviour has also been studied with an Indium beam of 158 GeV/c per nucleon. The beam test results are presented: the calorimeters response, the energy resolution and the localizing capability. Also the signal uniformity and a comparison between the transverse profile of the hadronic and electromagnetic shower are discussed. Moreover the differences between the ZP detector responses to protons and pions of the same energy have been investigated, exploiting the proton contamination in the positive pion beams. [ABSTRACT FROM AUTHOR]

Abstract: The details of the construction of the neutron Zero Degree Calorimeters (ZN) of the ALICE Experiment, as well as their performances, will be presented. These spaghetti calorimeters will measure the energy lost by spectator nucleons in heavy-ion collisions. They are made of an absorber (tungsten alloy) filled with silica fibers, in which the charged particles of the shower produce Cherenkov light. The final neutron calorimeters have been built and their performances studied at the CERN SPS using pion and positron beams with momentum ranging from 50 to 150GeV/. The main features like linearity of the response and resolution as a function of energy will be presented. [Copyright &y& Elsevier]

Abstract: The collision centrality in the ALICE experiment will be determined by the Zero Degree Calorimeters (ZDCs) that will measure the spectator nucleons energy in heavy ion collisions. The ZDCs detect the Cherenkov light produced by the fast particles in the shower that cross the quartz fibers, acting as the active material embedded in a dense absorber matrix. Test beam results of the calorimeters are presented. [Copyright &y& Elsevier]

ALICE at the CERN LHC will investigate the physics of strongly interacting matter at extreme energy densities where the formation of the Quark Gluon Plasma is expected. Its properties can be studied from observations like the production of mesons with charm and beauty quarks. These signals have to be studied as a function of energy density, which is determined by the centrality of collisions. One of the physics observables that is closely related with the centrality of the collision is the number of spectator nucleons that can be measured by the Zero Degree Calorimeters (ZDC). Having a direct geometric interpretation allows to extract the impact parameter with minimal model assumptions. This paper describes the readout system of the ZDC. The ZDC readout consists of a VME system with a ZDC Readout Card, a VME Processor, Discriminators, a ZDC Trigger Card, scalers, QDCs and TDCs. The system was successfully tested during the 2009 ALICE data taking and is currently operational at the LHC. [ABSTRACT FROM PUBLISHER]

The J/ ψ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed J/ ψ mesons at SPS energies. Hence, the measurement of J/ ψ elliptic anisotropy, quantified by the Fourier coefficient v2 of the J/ ψ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous J/ ψ suppression observed in Pb-Pb collisions. We present the measured J/ ψ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient v2 as a function of the collision centrality and of the J/ ψ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or pT sub-samples. The extracted v2 values are significantly larger than zero for non-central collisions and are seen to increase with pT. [ABSTRACT FROM AUTHOR]

Abstract: The trigger for the ALICE muon spectrometer will be issued by single-gap, low resistivity bakelite resistive plate chambers (RPCs). The trigger system consists of four RPC planes arranged in two stations, for a total of 72 detectors. One hundred and sixteen detectors have been assembled and tested in Torino. The tests have been performed with the streamer mixture developed for heavy ion data-taking. The tests include: the detection of gas leaks and parasitic currents; the measurement of the efficiency with cosmic rays, with particular regard to the uniformity of the efficiency throughout the whole active surface, with a granularity of about ; the measurement of the dark current and of the mean and localised noise rate. All the RPCs produced have been characterised. Among them, the detectors to be finally installed in ALICE and some spare have been selected; 17% of all the produced detectors have been discarded. A short description of the test set-up is given. The results of the tests are presented, with particular regard to the performance of the selected detectors. [Copyright &y& Elsevier]

ψ′ production is studied in Pb–Pb collisions at 158 GeV/c per nucleon incident momentum. Absolute cross-sections are measured and production rates are investigated as a function of the centrality of the collision. The results are compared with those obtained for lighter colliding systems and also for the J/ψ meson produced under identical conditions. [ABSTRACT FROM AUTHOR]

We report a new measurement of J/ψ, ψ′ and Drell–Yan cross-sections, in the kinematical domain -0.425

Abstract: The NA50 Collaboration has measured heavy-quarkonium production in p–A collisions at 450 GeV incident energy (). We report here results on the production of the ϒ states and of high-mass Drell–Yan muon pairs (). The cross-section at midrapidity and the A-dependence of the measured yields are determined and compared with the results of other fixed-target experiments and with the available theoretical estimates. Finally, we also address some issues concerning the transverse momentum distributions of the measured dimuons. [Copyright &y& Elsevier]

A dedicated front-end electronics has been developed for the trigger chambers of the ALICE muon spectrometer under construction at the future LHC at CERN. This trigger detector is based on RPCs (Resistive Plate Chambers) working in streamer mode. The number of electronics channels (about 21000) and the fact that RPC signals have specific characteristics have led to the design of an 8 channel front-end ASIC using a new discrimination technique. The principle of the ASIC is described and the radiation hardness is discussed. Special emphasis is put on production characteristics of about 4000 ASICs. [ABSTRACT FROM AUTHOR]

Charmonium suppression in Pb-Pb collisions at 158 GeV/c per nucleon is investigated in detail with the study of the transverse momentum distributions of J/ψ as a function of the centrality of the collision. It is shown that the observed J/ψ suppression in Pb-Pb interactions is particularly significant mainly at low transverse momentum where it strongly depends on centrality. For peripheral Pb-Pb collisions, the transverse momentum dependence of the J/ψ cross section is, as a function of centrality, qualitatively similar to the dependence observed in p-A and S-U collisions. Comparing peripheral and central Pb-Pb collisions, the data show a relative suppression in the whole pT range although its amplitude significantly decreases with increasing pT and becomes almost pT independent for the highest pT values. [Copyright &y& Elsevier]

We present a new measurement ofproduction in Pb-Pb collisions at 158 GeV/nucleon, from the data sample collected in year 2000 by the NA50 Collaboration, under improved experimental conditions with respect to previous years. With the target system placed in vacuum, the setup was better adapted to study, in particular, the most peripheral nuclear collisions with unprecedented accuracy. The analysis of this data sample shows that thecross-sections ratio measured in the most peripheral Pb-Pb interactions is in good agreement with the nuclear absorption pattern extrapolated from the studies of proton-nucleus collisions. Furthermore, this new measurement confirms our previous observation that thecross-sections ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb collisions and that this ratio persistently decreases up to the most central collisions. [ABSTRACT FROM AUTHOR]

ALICE, the experiment dedicated to the study of heavy ion collisions at LHC, will be equipped with a forward spectrometer to identify heavy quarkonium states from their decay into muons. The trigger system of the spectrometer consists of four planes of resistive plate chambers, front-end and fast-decision electronics. It is designed to reconstruct muon tracks in a large background environment and to provide a fast trigger signal to the spectrometer. We present results from the test of a trigger prototype that have been carried out with the muon beam of the CERN/SPS at the Gamma Irradiation Facility (GIF). The track finding efficiency as well as the robustness of the system to the uncorrelated background induced on the detector by the GIF source are discussed. Special emphasis is put on timing aspects which are crucial at LHC. A self-consistent method for timing optimization and monitoring is proposed. The findings, although specific to ALICE, are relevant to any muon trigger system operating at LHC. [ABSTRACT FROM AUTHOR]

The production of J/Ψand &Psi′ charmonium states in proton-nucleus interactions has been investigated by the NA50 experiment, at the CERN SPS. High statistics data sets were collected with collisions induced by 450 GeV protons incident on Be, Al, Cu, Ag and W targets. The J/ψand ψ production cross-sections have been determined for each p-A system and their dependences on the nucleus size have been studied, leading to the so-called normal nuclear absorption. Comparing the two patterns we see that the nuclear absorption is stronger for the &Psi′ than for the J/Ψ. Given the high statistics of the data samples, the xF (or rapidity) differential cross-sections of the J/Ψ and &Psi′ states have also been studied, for each of the target nuclei. [ABSTRACT FROM AUTHOR]

The trigger for the Dimuon Forward Spectrometer of the forthcoming ALICE experiment at CERN LHC will be provided by low-resistivity, single gap Resistive Plate Chambers working in streamer mode.Different ageing test were performed to measure and improve the life-time of the detector. Dummy chambers have been built to understand the effects of continuous gas flow upon the Bakelite resistivity: the results concerning our standard gas mixture (49% Ar, 40% forane, 7% isobutane and 4% SF6) are reported, and compared with the same mixture in which ∼1% of water vapor is added. Moreover, two ageing test of 1 month each have been carried out at the Gamma Irradiation Facility at CERN during 2001. The efficiency for cosmic rays under γ irradiation of RPCs coated with different thicknesses of linseed oil was measured. After protracted operation, the detectors have shown an increase of the current and of the background rate. The increase is slower in the chamber with a thicker oil coating. [Copyright &y& Elsevier]

In the framework of an R&D program on the ALICE dimuon trigger system, the spatial resolution of Resistive Plate Chambers working in streamer mode has been investigated during beam tests. Preliminary studies with cosmic rays had evidenced a dependence of the charge profile to the high voltage and to the gas mixture. However, the spatial resolution measured from the beam tests is only slightly varying with the high voltage and is close to the expected value w/√ of 12 where w is the strip pitch, for strips of 1 and 2 cm width. The probability to fire a strip as a function of the distance from the strip to the particle impact has been measured for various high voltages. A simple parametrisation of this probability has been achieved. This allows to predict, under various working condition, the cluster size distributions for RPCs with different strip widths and also to account for the effect of the particle incident angle. [Copyright &y& Elsevier]

Abstract: ALICE (a large ion collider experiment) is the LHC experiment dedicated to the study of ultra-relativistic heavy ion collisions. The ALICE muon spectrometer covers a large range in pseudo-rapidity and is designed to study quarkonia and heavy flavours decaying into (di-)muons. The high particle multiplicities environment in such collisions require a specific, fast and efficient trigger system, the muon trigger. It consists of four planes of RPC detectors, covering an area of 36m2 each, 21k front-end channels and a fast-decision electronics. The muon trigger is designed to reconstruct (muon) tracks and deliver a trigger signal each 25ns (40MHz) with a total latency of 800ns. The hit position on the RPC is measured in two orthogonal directions with an accuracy of about 1cm. The performance measured with the first p–p collisions at carried out in December 2009 is reported. [Copyright &y& Elsevier]