PARTICLE PHYSICS AND COSMIC RAY PHYSICS 47

The correlation lengths, determined for pairs of negative hadrons, are slightly larger than for S + A reactions, with the transverse momentum dependence more pronounced. The rapidity distribution of negative hadrons is still much wider than that expected for isotropic pion emission in the CM system (Fig.2).

1.13 Preparations for the CMS Experiment by M.Szeptycka, M.Gorski

In the year 1995, preparations for the CMS (Compact Muon Solenoid) experiment were continued. The preparations concerned the high energy muon triggering system. Two main aspects were addressed: 1. Construction and testing of the RPC (Resistive Plate Chamber) prototypes. In those chambers we will use a fast detector which should register the muon track and supply information to the triggering system. The work was done in collaboration with laboratories from Bari and Pavia. Several prototypes were constructed, partially from Polish materials. The chambers were tested at CERN in the H2 beam of the SPS accelerator. The main questions addressed were the chamber efficiency in high incident beam flux (in excess of 1 kHz/cm2), the chamber timing properties, and the usage of new freon gases which are allowed under the Montreal Convention. The chamber efficiency was found to be in excess of 90% at the high incoming rates. The time resolution was determined to be about 3 ns. The noise level of the chambers was also measured and found to be of the order of 10 Hz/cm2, which should not imperil the trigger operation. 2. The construction of the muon trigger processor integrated circuit. The collaboration with a group from the Warsaw Technical University was started. A feasibility study of the design of the triggering chip was performed. It was found that such a device can be constructed with available technologies. The Pattern Comparator (PAC) chip accepts data from four planes of the RPC devices and verifies the presence of hit patterns corresponding to the passage of the high energy muon tracks. The pattern set was obtained by the Monte Carlo study of the muon propagation in the CMS setup. The first prototype chip should be produced within two years. It operates in the pipelined mode, accepting data from the RPCs every 25 nanoseconds, which is the repetition rate of the LHC beam crossings. The results are output with the same frequency and the delay is several hundred nanoseconds, which is sufficient for triggering purposes. Due to the pipelined mode of operation, the trigger operates with no dead time.

1.14 Physics Goals of ALICE Project PL9701953 by K.Karpio, T.Siemiarczuk, G.Stefanek1*, L.Tykarski, G.Wilk and ALICE Collaboration

The heavy-ion detector ALICE (A Large Ion Collider Experiment) has emerged as a common design from the heavy-ion community curently working at CERN and a number of groups new to this field from both nuclear and high-energy physics. It currently includes about 560 physicsts from 63 institutions. ALICE has been designed as a dedicated heavy-ion experiment and its prime aim is the study of nuclear collisions at LHC. In order to establish and analyse the existence of QCD bulk matter and the Quark-Gluon Plasma, a number of observables have to be studied with ALICE in a systematic and comprehensive way. Some observables are needed to characterize the global features of the state created during the collision in order to constrain theoretical models (e.g. relevant degrees of freedom, size, lifetime, density, dynamic evolution). These observables yield information about the initial conditions and space-time evolution which is necessary in order to interpret a specific signal as a QGP signature or as an indication of new physics. Our strategy is to study a number of these specific signals together with global information about the events, in the same experiment. The signals accessible to our detector are summarized below according to the aspect of the collision on which they have a bearing: - Initial Conditions: global event features measure the number of colliding nucleons and give information on the energy density obtained. - Quark-Gluon Plasma: open charm production will probe the parton kinematics in the very early stage; prompt photons can reveal the characteristic thermal radiation from the plasma; the cross-section of high-p, hadrons is sensitive to the energy loss of the partons in the plasma; J/iJ; and T production probe deconfincment.