H.-Å. Gustafsson

The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events

The design, construction, and commissioning of the ALICE Time-Projection Chamber (TPC) is described. It is the main device for pattern recognition, tracking, and identification of charged particles in the ALICE experiment at the CERN LHC. The TPC is cylindrical in shape with a volume close to 90 m(3) and is operated in a 0.5T solenoidal magnetic field parallel to its axis. In this paper we describe in detail the design considerations for this detector for operation in the extreme multiplicity environment of central Pb-Pb collisions at LHC energy. The implementation of the resulting requirements into hardware (field cage, read-out chambers, electronics), infrastructure (gas and cooling system, laser-calibration system), and software led to many technical innovations which are described along with a presentation of all the major components of the detector, as currently realized. We also report on the performance achieved after completion of the first round of stand-alone calibration runs and demonstrate results close to those specified in the TPC Technical Design Report

Forward and transverse energy distributions in oxygen-induced reactions at 60 A GeV and 200 A GeV

Abstract Results are presented from reactions of 60 A GeV and 200 A GeV 16O projectiles with C, Cu, Ag, and Au nuclei. Energy spectra measured at zero degrees and transverse energy distributions in the pseudorapidity range from 2.4 to 5.5 are shown. The average transverse energy per participant is found to be nearly independent of target mass. Estimates of nuclear stopping and of attained energy densities are made.

The ALICE TPC front end electronics

In this paper we present the front end electronics for the time projection chamber (TPC) of the ALICE experiment. The system, which consists of about 570000 channels, is based on two basic units: (a) an analogue ASIC (PASA) that incorporates the shaping-amplifier circuits for 16 channels; (b) a mixed-signal ASIC (ALTRO) that integrates 16 channels, each consisting of a 10-bit 25-MSPS ADC, the baseline subtraction, tail cancellation filter, zero suppression and multi-event buffer. The complete readout chain is contained in front end cards (FEC), with 128 channels each, connected to the detector by means of capton cables. A number of FECs (up to 25) are controlled by a readout control unit (RCU), which interfaces the FECs to the data acquisition (DAQ), the trigger, and the detector control system (DCS). A function of the final electronics (1024 channels) has been characterized in a test that incorporates a prototype of the ALICE TPC as well as many other components of the final set-up. The tests show that the system meets all design requirements. Originally conceived and optimized for the time projection chamber (TPC) of the ALICE experiment, its architecture and programmability make this system suitable for the readout of a wider class of detectors.

Charged-particle distributions in 16O induced nuclear reactions at 60 and 200 A GeV

Abstract Results from 16 O induced nuclear interactions with C, Cu, Ag and Au targets at 60 and 200 A GeV are presented. Multiplicity and pseudorapidity-density distributions of charged particles and their dependence on the target mass number are reported. The increase in the particle density with increasing centrality, characterized by the energy flux at zero degrees, is investigated. Comparisons with the Fritiof model reveal systematic differences.

Centrality Dependence of Neutral Pion Production in 158A GeV

The production of neutral pions in 158AGeV Pb+Pb collisions has been studied in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied for the range 0.3 GeV/c<mT-m0<4.0 GeV/c. The results for central collisions are compared to various models. The centrality dependence of the neutral pion spectral shape and yield is investigated. An invariance of the spectral shape and a simple scaling of the yield with the number of participating nucleons is observed for centralities with greater than about 30 participating nucleons which is most naturally explained by assuming an equilibrated system.

^{208}

Abstract A sampling calorimeter designed for use at mid-rapidity in the relativistic heavy-ion experiment WA80 at CERN is described. Calibration and performance results are presented. Over the energy range of 2 to 50 GeV, the response of the mid-rapidity calorimeter was linear, and its energy resolution σ E was found to be given by 0.014 + 0.11 √E and 0.034+0.34 √E for electromagnetic and hadronic showers, respectively. Signal ratios of 1.2 and 1.4 were obtained for the e h ratio of the lead-scintillator electromagnetic section and the iron-scintillator hadronic section, respectively. The calorimeter provided an accurate transverse energy trigger. The response and resolution for high-energy heavy ions were slightly better than anticipated on the basis of the low-energy calibrations.

Pb+

Abstract We present test results on the use of thin ion implanted epitaxial Si detectors for registration of low- and medium-energy heavy fragments in nuclear reactions. A linear energy response for very low energy nuclei has been observed. A test of 10 μm + 300 μm telescopes under realistic experimental conditions for heavy ion experiments exhibits the possibilities to use these detectors for the measurements of multifragmentation products.

^{208}

The production of direct photons has been investigated in reactions ofp and16O projectiles at 60 and 200A·GeV with C and Au nuclei. Photon and π0 spectra have been measured in the pseudorapidity range 1.5≦η≦2.1 for the transverse momentum region 0.4 GeV/c≦pT≦2.8 GeV/c employing the lead-glass spectrometer SAPHIR. An upper limit of 15% at the 90% confidence level for the direct photon signal relative to the neutral pion production is obtained from the comparison of measured photon spectra with Monte Carlo simulations of the hadronic background based on the reconstructed yield of π0 and η mesons. Consequences for a possible phase transition to a quark-gluon plasma are discussed.

Pb Collisions

Transverse momentum (pT) distributions of inclusive photons and neutral pions at midrapidity are measured with a lead glass calorimeter in 60 and 200 A GeV16O+nucleus and proton+nucleus reactions. The variation of the average transverse momentum is investigated as function of centrality, determined by measurements of the remaining energy of the projectile and the charged particle multiplicity. For small values of the entropy, deduced from the multiplicity density, an increase in average pT is observed levelling off for larger values of entropy. The target-mass and energy dependence of π0 pT distributions are presented.

The mid-rapidity calorimeter for the relativistic heavy-ion experiment WA80 at CERN

Calibration and performance results are presented for a sampling calorimeter designed for use as a beam calorimeter at zero degrees in the relativistic heavy-ion experiment WA80 at CERN. This uranium-scintillator zero-degree calorimeter (ZDC) was found to have a linear response to heavy ions over the range 60–6400 GeV and an in-beam hadronic resolution ranging from σE = 0.013 + 0.33√E at low intensities to σE = 0.02 + 0.67√E at higher intensities. The eh ratio of the electromagnetic section was measured to be 1.12 at 135 GeV. The ZDC operated reliably with incident beams of 3.2 TeV oxygen and 6.4 TeV sulfur at intensities of over 106 nuclei per spill. It provided a trigger both for minimum bias events and for violent central collisions.