Search

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. Index Terms--Quartz optical fiber, radiation hardness, sampling calorimeter.

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. Index Terms--Application specific integrated circuit (ASIC), front-end electronics, large hadron collider (LHC), resistive plate chamber (RPC), streamer.

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. Index Terms--Dimuon, heavy ion collision, resistive plate chamber, timing, trigger.