R. Ferreira-Marques

Tests of CPT symmetry and quantum mechanics with experimental data from CPLEAR

Abstract We use fits to recent published CPLEAR data on neutral kaon decays to π + π − and πeν to constrain the CPT-violation parameters appearing in a formulation of the neutral kaon system as an open quantum-mechanical system. The obtained upper limits of the CPT-violation parameters are approaching the range suggested by certain ideas concerning quantum gravity.

A spark-protected high-rate detector

We developed a very low resistivity RPC-type detector, the anode of which was a plate made from materials with resistivity up to 5]107 ) cm, the cathode being a metallic mesh preceded by a drift region. In such a detector it was actually possible to combine the versatility and high counting-rate capability of metallic PPACs with the extreme robustness and ‘protectivenessa of Resistive Plate Chambers. Occasional discharges triggered by large deposits of primary ionisation or by extreme counting rates are quenched by the resistive anode and are constrained to the streamer phase of the sparking process. The study shows that this discharge a!ects the detector only locally and that the charge released is limited to a few tens of nC. Proportional counting rates up to 105 Hz/mm2 were achieved at gains above 104. The energy resolution at 6 keV was 20% FWHM. The observed gain-rate trade-o! is well described by an analytic model and further improvements may be expected by lowering the resistivity of the anode material. The properties of several custom-made, controllable resistivity, anode materials are described and prospects of improvement in the performance of the detector are discussed. ( 1999 Elsevier Science B.V. All rights reserved.

A large area timing RPC

Abstract A large area Resistive Plate Chamber (RPC) with a total active surface of 160×10xa0cm 2 was built and tested. The surface was segmented in two 5xa0cm wide strips readout on both ends with custom, very high frequency, front-end electronics. A timing resolution between 50 and 75xa0ps σ with an efficiency for Minimum Ionizing Particles (MIPs) larger than 95% was attained over the whole active area, in addition with a position resolution along the strips of 1.2xa0cm. Despite the large active area per electronic channel, the observed timing resolution is remarkably close to the one previously obtained (50xa0ps σ ) with much smaller chambers of about 10xa0cm 2 area. These results open perspectives of extending the application of timing RPCs to large area arrays exposed to moderate particle multiplicities, where the low cost, good time resolution, insensitivity to the magnetic field and compact mechanics may be attractive when compared with the standard scintillator-based Time-of-Flight (TOF) technology.

Physics at CPLEAR

LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of , and symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved.

Evaluation of the phase of the CP violation parameter η+− and the KL - KS mass difference from a correlation analysis of different experiments

Abstract The best estimation of ϕ +− (the phase of the CP violation parameter η +− ) and of Δm (the K L - K S mass difference) is obtained by averaging the results of different experiments, taking into account the different correlation, existing for most of the experiments, between the measurement of ϕ +− and Δm . Including the recent measurements, we obtain the average values 〈Δm〉 = (530.7 ± 1.3) × 10 7 ħ/s and 〈 ϕ +− 〉 = 43.82° ± 0.63°. This value of ϕ +− is in good agreement with the superweak phase ϕ SW = 43.49° ± 0.08°.

Measurement of the neutral kaon regeneration amplitude in carbon at momenta below 1 GeV/c

The neutral kaon regeneration amplitude in carbon at momenta between 250 and 750~MeV/

Single-electron pulse-height spectra in thin-gap parallel-plate chambers

c

The CPLEAR particle identification detector

was determined by measuring the interference of inherent and coherently regenerated PKS amplitudes. This interference appears in the rates of initially pure (tagged) PKz and PaKz decaying to PgppPgpm after crossing a carbon absorber.