C. Joseph

Use of a neural network to exploit light division in a triangular scintillating crystal

Abstract This work presents a novel way of exploiting light division in a scintillating crystal to localise the point of interaction using a neural network. Because sensitivity at the centre of a positron tomograph would be significantly increased for a spherical geometry compared to a cylinder with the same area of detection, we explored the possibility of developing a position-sensitive triangular block detector that might be used ultimately as an element of a spherical shell. With 3 PMTs coupled on each side of a triangular BaF 2 crystal of about 8 cm 2 × 1 cm, we obtain spatial resolutions less than 4 mm FWHM over the whole surface of the triangle and energy resolutions of about 14% FWHM for 662 keV impinging photons. Experimental measurements are compared with Monte Carlo simulations and prospects for different configurations are discussed.

Direct photon cross sections in proton-proton and antiproton-proton interactions at s=24.3 GeV

Abstract We report results on inclusive direct photon (γ),π0, and η production in both pp and pp interactions at s =24.3 GeV in the transverse momentum range 4.1≤pT≤7.7 GeV/c and rapidity range −0.1≤y≤0.9. The data were collected between 1988 and 1990 by the UA6 experiment at CERN, which employed an internal H2 gas jet target in the SppS collider. The inclusive direct photon cross sections and the cross section difference σ( p p )−σ( pp ) expressed as functions of pT(γ) are compared with next-to-leading order QCD predictions.

Determination of αs and the gluon distribution using direct photon production in pp and pp collisions

Abstract Direct photon cross sections obtained in p p and pp collisions at √s = 24.3 GeV at the CERN SPS, are used in a next-to-leading order QCD analysis. From the cross-section difference σ( p p → γX) − σ (pp → γX) , and quark distributions measured in deep inelastic scattering, a determination of the strong coupling constant, αs, is performed via a measurement of Λ (4) MS . This first measurement of Λ (4) MS using direct photon data yields a value Λ (4) MS = 235 ± 79 (stat.) ± 70 (syst.) MeV. The corresponding value of αs expressed at MZ2 is αs (MZ2) = 0.112±0.006 (stat.)±0.005 (syst.)−0.001+0.009 (theor.). The gluon distribution in the proton for x > 0.2 is determined both from the p p and from the pp data, and the results agree with each other and with previous determinations using the same method.

Measurement of the inclusive J / psi production cross-sections in anti-p p and p p collisions at s**(1/2) = 24.3-GeV

Abstract The inclusive cross section times branching ratio for J/ψ→e + e − has been measured in the forward region in the UA6 experiment for p p and pp collisions at √ s = 24.3 GeV. The ratio of the pp to p p cross sections is found to be 0.76 ± 0.14 ± 0.06. This demonstrates that gluon-gluon fusion dominates over quark-antiquark annihilation in the formation of the c c state.

Experimental study of an impact-parameter optical discriminator

Abstract An optical discriminator, sensitive to the impact parameter has been tested in a particle beam. The device is based on the detection of Cherenkov light produced and trapped in a thin spherical crystal shell viewed by a fast photodetector. The detector is only sensitive to charged particles with a nonzero impact parameter relative to the centre of the crystal sphere. A prototype using a LiF crystal has been tested and the experimental results are in agreement with expectations. We outline the foreseen developments in order to use such a detector for a fast selection of B events in fixed-target experiments at proton accelerators. We also discuss the use of the detector as presently conceived for the fast selection of strange particles.

Direct photon production in pp and pp interactions at √s=24.3 GeV

Abstract Inclusive direct photon invariant cross sections have been measured in both p p and pp collisions at √ s = 24.3 GeV at the CERN SPS, permitting the first measurement of the difference of the p p and pp cross sections. The direct photon cross section in p p collisions has been found to be systematically larger than that in pp collisions, which indicates a significant contribution of the q q annihilation term as predicted by theoretical calculations.

Results of a first beam test of hadron blind trackers

Abstract We describe the experimental results of a new type of electron tracker, called Hadron Blind Detector or HBD. An HBD prototype was tested with gas mixtures of CF4 with He or Ne and a parallel plate avalanche chamber having a CsI photocathode of eight pads. Beam tests confirm the large Cherenkov light bandwidth in the EUV region that can be obtained with such gas mixtures. It results in a large quality factor of about 500 cm−1 which allows HBD operation with a much shorter radiator thickness than conventional Cherenkov counters. Full electron efficiency was obtained, while pions were rejected up to momenta of 9 GeV/c. HBD is unique in measuring electron trajectories near the vertex, vetoing Dalitz pairs, and providing trigger on electrons among heavy hadron background. We discuss the use of such detectors for lepton identification and detection in high energy physics experiments and especially in heavy ion colliders.

A new determination of αs using direct photon production cross sections in pp and p̄p collisions at s=24.3 GeV

CERN-PBAR/P accelerator. A NEW DETERMINATION OF ALPHA(S) USING DIRECT PHOTON PRODUCTION CROSS-SECTIONS IN P P AND ANTI-P P COLLISIONS AT S**(1/2) = 24.3-GEV.

A New determination of

CERN-PBAR/P accelerator. A NEW DETERMINATION OF ALPHA(S) USING DIRECT PHOTON PRODUCTION CROSS-SECTIONS IN P P AND ANTI-P P COLLISIONS AT S**(1/2) = 24.3-GEV.

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Abstract New results from the tests of the impact parameter discriminator by the RD30 Collaboration are presented. The device, based on the detection of Cherenkov light produced in a thin crystal, is able to cope with extremely high rates in the GHz range and sign tracks with non-zero impact parameter at a first trigger level. We report experimental results obtained with a sapphire shell surrounded by a liquid cladding compensating chromatic dispersion. An excellent signal to background ratio has been obtained and the sensitivity at low impact parameters reaches the requirements for efficient B-meson selection. The use of such a device for hyperon selection will also be discussed.