Giles Barr

Abstract:

A new precision measurement of the Ξ0 mass has been performed at the NA48 experiment at the CERN SPS. The value obtained is [1314.82±0.06 (stat.) ±0.2 (syst.)] MeV/c2. The branching ratios of Xi;0 radiative decays have been measured as: Br(Ξ0 → Λγ) = [1.90 ± 0.34(stat.) ± 0.19(syst.)] · 10-3 and Br(Ξ0 → ∑0γ) = [3.14 ± 0.76(stat.) ± 0.32(syst.)] · 10-3.

Abstract:

The NA48 experiment at the CERN SPS accelerator is making a measurement of the direct CP violation parameter e//£by compari ng the four rates of decay of Kä andKJ. into 2n° and 7i+7iT. To reconstruct the decays into 27C11 the information from the almost 13500 channels of a quasi-homogeneous liquid krypton electromagnetic calorimeter is used. The readout electronics of the calorimeter has been designed to provide a dynamic range from a few MeV to about 50 GeV energy deposition per cell, and to sustain a high rate of incident particles. The system is made by cold charge preamplifiers (working at 120°K), low-noise fast shapers followed by digitizer electronics at 40 MHz sampling rate that employs a gain switching technique to expand the dynamic range, where the gain can be selected for each sample individually (i. e. every 25 ns). To reduce the amount of data collected the system contains a zero suppression circuit based on halo expansion. © 2000 IEEE.

Abstract:

The subject of space charge due to positive ions slowly moving in parallel plate ionization chambers is considered. A model for the degradation of the detector response is developed, with particular emphasis on electromagnetic calorimeters .The topics discussed include: (a) the stationary; (b) the time dependent cases; (c) the limit of very large space charge; (d) the electric field dependence of the electron drift velocity; (e) the effect of longitudinal development of showers; (f ) the behaviour of the average reductions of response; and (g) the non-uniformity of response for different positions of the shower axis inside the cell defined by the electrodes. The NA48 calorimeter is used as application and for comparison of results. © 1999 Elsevier Science B.V. All rights reserved.

Abstract:

We present the results for a direct search for light gluinos through the appearance of η→3π0 with high transverse momentum in the vacuum tank of the NA48 experiment at CERN. We find one event within a lifetime range of 10-9-10-3 s and another one between 10-10-10-9 s. Both events are consistent with the expected background from neutrons in the beam, produced by 450 GeV protons impinging on the Be targets, which interact with the residual air in the tank. From these data we give limits on the production of the hypothetical gg̃ bound state, the R0 hadron, and its R0→ηγ + ̃ decay in the R0 mass range between 1 and 5 GeV. © 1999 Elsevier Science B.V. All rights reserved.