ALICE (A Large Ion Collider Experiment) is an experiment at the Large Hadron Collider (LHC) optimized for the study of heavy-ion collisions, at a centre of mass energy ∼ 5.5 TeV. The prime aim of the experiment is to study in detail the behaviour of matter at high densities and temperatures, in view of probing deconfinement and chiral symmetry restoration. The detector consists essentially of two main components: the central part, composed of detectors mainly devoted to the study of hadronic signals and dielectrons in the pseudorapidity range −1 <η< 1, and the forward muon spectrometer, devoted to the study of quarkonia behaviour in dense matter. The layout of the ALICE set-up is shown in colour Fig. 1.i. The first technical challenge is imposed by the large number of particles created in the collisions of lead ions. There is a considerable spread in the presently available predictions for the multiplicity of charged particles produced in a central Pb–Pb collision. The design of the experiment has been based on the highest value, 8000 charged particles per unit of rapidity, at mid rapidity. This multiplicity dictates the granularity of the detectors and their optimal distance from the colliding beams. The detailed characterization of ion–ion collisions requires particles to be measured and identified over a large range of momenta and masses. This second challenge has determined the rather complex particle identification scheme of ALICE.

The STAR-RICH detector extends the particle identification capabilities of the STAR experiment for charged hadrons at mid-rapidity. This detector represents the first use of a proximity-focusing CsI-based RICH detector in a collider experiment. It provides identification of pions and kaons up to 3GeV/c and protons up to 5GeV/c. The characteristics and performance of the device in the inaugural RHIC run are described.

An algorithm for the recognition of Cherenkov patterns based on the Hough Transform Method is presented. It basically consists in a mapping of the pad coordinate apace directly to the Cherenkov angle parameter space with a crucial increase of performance in the treatment of different pattern shapes and amount of background, The method has been developed in the framework of the ALICE experiment at CERN. for the analysis of data taken with the High Momentum Particle Identification Detector RICH prototype in the test beam. (C) 2002 Elsevier Science B.V. All rights reserved.

We report on the R&D studies performed on a CsI-based RICH detector with a liquid perfluorohexane radiator running pure methane at atmospheric pressure. The development, initiated by the CERN RD26 project in 1993, has been pursued in the framework of the ALICE/HMPID collaboration. A prototype of the detector under construction for ALICE is taking data since two years in the STAR experiment at RHIC.

The STAR-RICH detector extends the particle identification capabilities of the STAR spectrometer for charged hadrons at mid-rapidity. It allows identification of pions and kaons up to similar to3 GeV/c and protons up to similar to5 GeV/c. The characteristics and performance of the device in the inaugural RHIC run are described.

A RICH detector with a CsI photo-cathode and liquid perfluorohexane radiator has been installed in the STAR experiment at RHIC. The liquid is continuously cleaned and distributed to a quartz containment vessel within the detector by a closed recirculation system. A VUV spectrometer is connected to the system which monitors the optical transparency of the liquid. This measurement provides one of the pieces of information necessary to model the number of Cherenkov photons which reach the pad plane. A description of the liquid recirculation system and the cleaning procedure for the liquid as well as the spectrometer is presented along with results of their performance.

The study of the production of charged particles at high transverse momenta plays an important role in the understanding of the interaction mechanism of high-Et jets with the dense nuclear matter.A prototype of a RICH (Ring Imaging CHerenkov) detector developed in the framework of the CERN-ALICE experiment has been fully integrated in the STAR experiment at RHIC (BNL). It allows identification of primary charged particles (namely pi, K and p) extending the region of acceptance of the experiment to medium-high transverse momenta (p(t) < 2.5 GeV/c for pi and K, p(t) < 5 GeV/c for protons).Methods of pattern recognition and identification of charged particles using the RICH will be presented. Preliminary results on identified charged particle ratios at midrapidity and 1.5 < p(t) < 2.5 GeV/c will be also shown.

The optimization of the HMPID RICH geometrical parameters has been performed with beam tests and Monte Carlo simulations. The results show that with a radiator having 50% larger thickness than the 10 mm so far adopted, the detector can be operated at a gain reduced by the same factor, thus decreasing the photon feedback background and improving the stability of operation in presence of heavily ionizing events. In addition, the use of a low gain has the remarkable advantage of providing a reserve of photoelectrons which could be exploited by increasing the gain, in the case of a degradation of the CsI photocathodes quantum efficiency.

A 1 m2 CsI RICH prototype has been successfully tested in a hadron beam at CERN SPS. The prototype, fully equipped with 15k electronic channels, has been used to identify particles coming from π-Be interactions. Track reconstruction has been performed by using a telescope consisting of four gas pad chambers. A detailed description of the detector will be presented and results from test will be discussed.

A pattern recognition method developed for the High Momentum Particle IDenti"cation (HMPID) detector in the ALICE experiment at CERN is presented. The algorithm is based on the Hough transform with a mapping of the pad coordinate space directly to the Cherenkov angle parameter space. Cherenkov angle reconstruction has been studied as a function of di!erent particle densities in the photodetector using real data taken in the ALICE tests at the CERN SPS: a satisfactory resolution can be achieved even in events where the occupancy reaches more than 12%, which is the situation we may be confronted with in central Pb}Pb interactions at LHC. ( 1999 Elsevier Science B.V. All rights reserved.

A pattern recognition method developed for the High Momentum Particle IDentification (HMPID) detector in the ALICE experiment at CERN is presented. The algorithm is based on the Hough transform with a mapping of the pad coordinate space directly to the Cherenkov angle parameter space. Cherenkov angle reconstruction has been studied as a function of different particle densities in the photodetector using real data taken in the ALICE tests at the CERN SPS: a satisfactory resolution can be achieved even in events where the occupancy reaches more than 12%, which is the situation we may be confronted with in central Pb–Pb interactions at LHC.

We present the performances of large area CsI-RICH prototypes obtained in single-particle events. The differential quantum efficiency of the photocathodes has been deduced from Cherenkov rings by means of two different procedures: a direct measurement with a thin NaF radiator and a Monte Carlo-based estimation for a C6F14 radiator. A factor of merit of 45 cm−1 has been found for the typical detector configuration. Two angle reconstruction algorithms have been used and the different errors affecting the Cherenkov angle resolution have been estimated combining the analytical treatment and the Monte Carlo simulation. Also the dependence on radiator thickness, Cherenkov ring radius, chamber voltage and particle incidence angle has been studied.

A high momentum particle identification detector (HMPID) covering about 5% of the ALICE central barrel region has been designed and prototyped. The detector consists of seven RICH modules with a proximity focusing geometry, covering 12 m2. The very large density of hits on the detector (80÷90 part/m2 in the extreme cases) makes the recognition of the Cherenkov photon patterns a complex and crucial task. A study of the pattern recognition strategy based on the Hough transformation in terms of particle identification efficiency and particle contamination will be presented.

The maximum expected particle density in the HMPID modules (corresponding to an occupancy of about 12%) requires the development of powerful pattern recognition methods for the reconstruction of Cherenkov rings and angles associated to each charged track in ALICE. In the present note we describe a study performed onto real data taken in ALICE tests at the SPS during the past two years. The method used is based on the Hough transform with a mapping of the pad coordinate space directly to the Cherenkov angle parameter space. The results for the Cherenkov angle resolution obtained by applying the method over data samples with di erent experimental conditions are reported.