J. Waterhouse

Inclusive photoproduction of single charged particles at highp T

Single charged-particle inclusive cross sections for photon, pion and kaon beams on hydrogen at the CERN-SPS are presented as functions ofpT andxF. Data cover the range 0.0<pT<5.0 GeV/c and 0.0<xF<1.0 at incident momenta from 70 to 170 GeV/c. The comparison between photon- and hadron-induced data indicates a relative excess of particles withpT>1.6 GeV/c for the photon-induced data. Using the hadron-induced data to estimate the hadronic behaviour of the photon, the difference distributions and ratios of cross sections are a measure of the contribution of the point-like photon interactions. The data are compared with QCD calculations and show broadly similar features.

Measurements of the anisotropy ratio between longitudinal and transverse diffusion in argon based gas mixtures

Abstract A special drift cell with proportional wire readout has been constructed to make simultaneous measurements of the drift velocity, the longitudinal and this ratio with percentage of quencher used, and also compare favourably with existing Monte Carlo models. A simple method of parametrizing the data is suggested that should allow prediction of the diffusion properties given the drift velocity.

Comparison of photon and hadron induced production of ρ0 mesons in the energy range of 65 to 175 GeV

The inclusive production of ρ0 mesons was measured in γp andh±p collisions at beam energies of 65 GeV≦Eγ≦175 GeV andEh=80, 140 GeV, respectively, whereh is π orK. Cross sections were determined for all beams and energies as functions ofxF (−0.1≦xF≦1.0),pT (0≦pT≦3.5 GeV/c) and the polar decay angle of the ρ0 by fitting the ρ0 signal in π+π- mass distributions. The ρ0 line shape is found to be distorted from a pure Breit-Wigner distribution throughout most of thexF−pT plane for both photon and hadron beams and a simple explanation is suggested. Throughout the paper emphasis is put on the comparison of photon and hadron beam data. The comparison of cross sections of γp andhp data provides a measure of the Vector Meson Dominance factor throughout thexF−pT range of the ρ0. The ρ0 production at lowpT can be described for both photon and hadron beams by a triple regge model at largexF. Similarly central production is well described by the quark-antiquark fusion model. At largepT there is an excess of ρ0 photoproduction which is consistent with the expected onset of pointlike photon interactions.

The OPAL vertex drift chamber

Abstract A high precision vertex drift chamber has been installed in the OPAL experiment at LEP. The design of the chamber and the associated readout electronics is described. The performance of the system has been studied using cosmic ray muons and the results of these studies are presented. A space resolution of 50 μm in the drift direction is obtained using the OPAL central detector gas mixture at 4 bar.

Inclusive production of π0-mesons in πp,Kp and γp collisions at energies around 100 GeV

Measurements are reported of inclusive production of π0-mesons in the beam fragmentation region in γp, πp andKp collisions. Results include the ratio of π0 production inKp and πp collisions, showing reduced production from fragmentation of theK-meson, and the ratio of π0 production in photon and hadron collisions which shows agreement with modified Vector Meson Dominance at lowPT, and departures at higherPT signalling the onset of direct photon reactions. The pattern of departure from Feynman scaling at highPT points to a contribution of hard parton-parton collisions in both γp and πp collisions.

A study of the point-like interactions of the photon using energy-flows in photo- and hadro-production for incident energies between 65 and 170 GeV

Energy-flow distributions for charged hadrons from interactions of photons, pions and kaons on hydrogen are presented as functions of ΣpT2 in the event plane. Data cover the range 0.0<ΣpT in2<10.0(GeV/c)2 and 0.0<xF<1.0 for beam momenta from 65 to 170 GeV/c. The comparisons between photon-and hadron-induced data show an excess of events with larger ΣpT in2 for the photon-induced data. Using the hadron-induced data to parameterise the hadronic behaviour of the photon, the differences between cross sections are used to measure the contribution of the point-like photon interactions. Quantitative calculations of the point-like photon interactions using the Lund Monte-Carlo program LUCIFER, based on QCD, are in agreement with the data.

The OPAL vertex detector prototype

The prototype test results of a high resolution charged particle tracking detector are reported. The detector is designed to measure vertex topologies of particles produced in the e+e− collisions of the OPAL experiment at LEP. The OPAL vertex detector is a 1 m long, 0.46 m diameter cylindrical drift chamber consisting of an axial and stereo layer each of which is divided into 36 jet cells. A prototype chamber containing four axial and two stereo cells was studied using a pion test beam at CERN. The studies examined the prototype under a variety of operating conditions. An r−φ resolution of 60 μm was obtained when the chamber was operated with argon (50%)-ethane (50%) at 3.75 bar, and when CO2(80%)-isobutane (20%) at 2.5 bar was used a 25 μm resolution was achieved. A z measurement using end-to-end time difference has a resolution of 3.5 cm. The details of these prototype studies are discussed in this paper.

PRODUCTION OF F2(1270) AND F0(975) MESONS BY PHOTONS AND HADRONS OF ENERGY 65-175 GEV

AbstractMeasurements are reported of inclusivef2(1270) andf0(975) production in γp, π±p andK±p collisions at photon beam energies of 65 to 175 GeV and hadron beam energies of 80 and 140 GeV. Thef2 andf0 mesons were found at masses of 1.250 GeV and 0.961 GeV respectively. Inclusivef2 production at lowxF was found to have a similarpT dependence for each beam type, whereas an additional pion-exchange contribution was found for production by pions at highxF. Cross sections are compared with those for ρ0 production and give no indication of a non-q

Forward charge asymmetry in low-P T photoproduction of hadrons

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