J. Boissevain

The L3 silicon microvertex detector

Abstract The design and construction of the silicon strip microvertex detector (SMD) of the L3 experiment at LEP are described. We present the sensors, readout electronics, data acquisition system, mechanical assembly and support, displacement monitoring systems and radiation monitoring system of the recently installed double-sided, double-layered SMD. This detector utilizes novel and sophisticated techniques for its readout.

Temperature dependence of radiation damage and its annealing in silicon detectors

Silicon detectors at future collider facilities such as the Superconducting Super Collider (SSC) will be exposed to large fluences of both neutral and charged particles, resulting in considerable bulk radiation damage. In order to reduce the increase in leakage current associated with that damage, the proposed operating temperature of the silicon detectors in the SSC Solenoidal Detector Collaboration (SDC) experiment is 0 degrees C. In order to explore any potential complications of operating detectors at 0 degrees C, two sets of detectors were irradiated. One set was kept close to 0 degrees C during the exposure and annealing period, while the other was maintained at room temperature throughout ( approximately 27 degrees C during the exposure, and approximately 23 degrees C during the annealing period). The full depletion voltage and leakage current of the detectors during the irradiation period and over the subsequent annealing period were monitored. It is concluded that detectors will have to be operated at 0 degrees C, and, once damaged, be maintained at 0 degrees C in order to keep their operating voltage at a reasonable value ( >

Identified pion interferometry in heavy-ion collisions at CERN

Abstract π + π + correlations from S + Pb collisions at 200 GeV/ c per nucleon, measured by the focusing spectrometer of the NA44 experiment at CERN, are presented. The large data set, particularly at small values of Q inv , allows determination of the detailed shape of the correlation function. We construct the background by event mixing, and correct for resolution, Coulomb interaction, and distortion of single-particle spectra which produce effects large compared to the statistical errors at small Q inv . An exponential, rather than gaussian, source distribution is slightly favoured, but both are statistically acceptable.

Mid-rapidity protons in 158A·GeV Pb+Pb collisions

Abstract Proton distributions at mid-rapidity (2 ≤ y ≤ 3) have been measured for 158A·GeV Pb+Pb collisions in the focusing spectrometer experiment NA44 at CERN. From baryon number conservation and by comparing the experimentally measured d N d y distribution with the transport model RQMD, we conclude that a rather high degree of nuclear stopping has been reached for the truly heavy-ion collisions at these energies. Transverse mass distributions exhibit characteristically thermal shapes and the slope parameters increase with the mass of the colliding system.

Use of aerogel for imaging Cherenkov counters

Abstract In the past, detectors using silica aerogel as a Cherenkov radiator treated this material as a diffuse source of Cherenkov photons. In this paper we report on measurements made to explore the feasibility of using aerogel for imaging Cherenkov purposes. The results of the measurements are reproduced by a detailed Monte Carlo. This allows us to identify parameters critical for the use of aerogel as a radiator in imaging detectors. We conclude that commercially available aerogel can be used for these purposes.

Three Pion Correlations in Sulphur Lead Collisions at the CERN SPS

Abstract π + π + π + correlations from sulphur-lead collisions at 200 GeV/c per nucleon are presented as measured by the focusing spectrometer of experiment NA44 at CERN. We have investigated the three-pion correlation function at mid-rapidity and found that a genuine three-body correlation is suppressed. A possible interpretation of this result is that the emission of particles is partially coherent.

Coulomb effect in single particle distributions

Abstract Single particle distributions from heavy-ion collisions show the effect of Coulomb interactions on the final state. While a rather strong effect is seen in the ratio π − π + from central 158A·GeV/c Pb+Pb collisions, at most a small enhancement is found in the ratios from S+S and S+Pb collisions at 200A·GeV/c.

Directional dependence of the pion source in high-energy heavy-ion collisions

Abstract π + π + and π − π − correlations from 200 GeV per nucleon S + Pb collisions and π + π + correlations from 450 GeV p + Pb collisions measured by the focussing spectrometer of CERN experiment NA44 are presented. The large data set which emphasizes small values of momentum difference allows multi-dimensional analysis along with the more traditional one-dimensional parameterization to characterize the pion emission source. It is found that the three radius parameters are similar and large compared to the projectile radius. This can be explained by pion scattering in the final state hadronic system.

Kaon interferometry in heavy ion collisions at the CERN SPS

K+K+ and K−K− correlations from S+Pb collisions at 200 GeV/c per nucleon and K+K+ correlations from p+Pb collisions at 450 GeV/c per nucleon, are presented as measured by the focusing spectrometer of the NA44 experiment at CERN. Multidimensional fits are performed in order to characterize the kaon-emission volume, which is found to be smaller than the pion-emission volume.

Particle ratios from central Pb + Pb collisions at the CERN SPS

We will address the physics of K?/K+ and /p ratios measured in 158 A GeV Pb + Pb collisions as a function of centrality and transverse momentum. We observe little significant centrality dependence in neither K?/K+ nor /p ratios and they are almost constant as a function of PT. In addition to the chemical freeze-out temperature Tch, we extract the chemical potentials for both light and strange quarks (?q and ?s) by comparing the present data with simple model predictions. Tch is greater than the thermal freeze-out temperature which is extracted from the transverse momentum distribution of charged hadrons.