Two-particle correlations of direct photons were measured in central 208Pb+208Pb collisions at 158A GeV. The invariant interferometric radii were extracted for 100<K(T)<300 MeV/c and compared to ...radii extracted from charged pion correlations. The yield of soft direct photons, K(T)<300 MeV/c, was extracted from the correlation strength and compared to theoretical calculations.
Results on transverse mass spectra of neutral pious measured at central rapidity are presented for impact parameter selected 158-A GeV Pb + Pb-1 and Pb + Nb collisions. The distributions cover the ...range 0.5 GeV/c(2) less than or equal to MT - Mo less than or equal to 4 GeV/c(2). The change of the spectral shape and the multiplicity with centrality is studied in detail. In going from p+p to semi-peripheral Pb+Pb collisions there is a nuclear enhancement increasing with transverse mass similar to the well known Cronin effect, while for very central collisions this enhancement appears to be weaker than expected.
The Alice time projection chamber (TPC) detector will be operated with a gas mixture of 90% Ne and 10% CO 2 at the electric field of 400 V/cm. Recent studies favor a three-component mixture by adding ...about 5% N 2 , which will improve the stability of the gas against discharges. These operating parameters lead to a nonsaturated drift velocity for electrons but also impose that all external influences on the drift gas must be reduced to minimum. A problematic influence is the temperature variation, which can lead to local fluctuation in the gas density and therefore directly affects the drift velocity. For the Alice TPC, the aim is to have a temperature stability of 0.1degC over the full drift length (2.5 m). The main heat contribution comes from the readout chambers' front-end electronics and one estimates that a total of 30.2 kW must be removed. In this paper we present the cooling strategies for the TPC and discuss the results of the thermal test setup build for validation
Event-by-event fluctuations in the multiplicities of charged particles and photons, and the total transverse energy in 158A GeV Pb+Pb collisions are studied for a wide range of centralities. For ...narrow centrality bins the multiplicity and transverse energy distributions are found to be near perfect Gaussians. The effect of detector acceptance on the multiplicity fluctuations has been studied and demonstrated to follow statistical considerations. The centrality dependence of the charged particle multiplicity fluctuations in the measured data has been found to agree reasonably well with those obtained from a participant model. However, for photons the multiplicity fluctuations have been found to be lower compared to those obtained from a participant model. The multiplicity and transverse energy fluctuations have also been compared to those obtained from the VENUS event generator.
Directed and elliptic flow of inclusive photons near mid-rapidity in 158
A GeV Pb
+
Pb collisions has been studied. The data have been obtained with the photon spectrometer LEDA of the WA98 ...experiment at the CERN SPS. The flow strength has been measured for various centralities as a function of
p
T
and rapidity over
0.18
<
p
T
<
1.5
GeV
/
c
and
2.3
<
y
<
2.9
. The angular anisotropy has been studied relative to an event plane obtained in the target fragmentation region that shows the elliptic flow to be in-plane. The elliptic flow has also been studied using two-particle correlations and shown to give similar results. A small directed flow component is observed. Both the directed and elliptic flow strengths increase with
p
T
. The photon flow results are used to estimate the corresponding neutral pion flow.
The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in Pb-208 + Pb-208 collisions at 158 (.) A GeV/c in the WA98 ...experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.
Timing performance of spark counters and photon feedback Pestov, Yu.N; Schmidt, H.R; Schreiber, B
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2000, Letnik:
456, Številka:
1
Journal Article
Recenzirano
Odprti dostop
It was shown experimentally that delayed signals from the spark counters (“tail problem”) could be connected with low-gain avalanches. The development of these avalanches is stopped by the anode ...electrode but they still have a chance to produce a delayed streamer by photon feedback. Good absorption characteristics of the gas mixture at wide photon energy range (starting from a cathode work function up to the X-ray region) and a high cathode work function value reduce the tail.
Azimuthal correlations of photons produced at mid-rapidity in 200 A GeV S + Au collisions have been studied using a preshower photon multiplicity detector in the WA93 experiment. The Fourier ...expansion method has been employd to estimate the event plane via the anisotropy of the event as a function of centrality. The event plane correlation technique has been used to determine the true event anisotropy, beyond the anisotropy which arises due to finite multiplicity. The VENUS event generator with rescattering and proper simulation of the detector response can explain only a portion of the observed anisotropy. The residual anisotropy is found to be of the order of 5% for semi-central collisions. This suggests that directed collective flow of the produced particles is present at SPS energies.
The Alice TPC detector will be operated with a gas mixture of 90% Ne and 10% CO/sub 2/ at the electric field of 400 V/cm. Recent studies favor a three-component mixture by adding about 5% N/sub 2/, ...which will improve the stability of the gas against discharges. These operating parameters lead to a non-saturated drift velocity for electrons but also impose that all external influences on the drift gas must be reduced to minimum. The most problematic influence is temperature variation, which can lead to local fluctuation in the gas density and therefore directly affects the drift velocity. For the Alice TPC, the aim is to have a temperature stability of 0.1/spl deg/C over the full drift length (2.5 m). The main heat contribution comes from the readout chambers front-end electronics and one estimates that a total of 30.2 kW must be removed. The test results discussed here give qualitative and quantitative information about the thermal behavior of the chambers for validation of the TPC cooling strategy.
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