O. Runolfsson

ExperimentalJ/ψ hadronic production from 150 to 280 GeV/c

A detailed study ofJ/ψ hadronic production has been performed in a high statistics experiment (more than 1.5 106J/ψ observed in their dimuon decay mode). Data have been taken with incident π±,K±,p±, on hydrogen and platinum targets, at 150, 200 and 280 GeV/c. We find from the observed nuclear dependance of the cross sections, that about 18% of theJ/ψ are produced diffractively. Using known structure functions of the quarks in the nucleon and in the pion, we derive estimations for the gluon structure functions.

The OPAL silicon microvertex detector

A silicon strip microvertex detector has been designed, constructed and commissioned in the OPAL experiment at the LEP electron-positron collider. The microstrip devices incorporate a new FoxFET biassing scheme developed together with Micron Semiconductor Ltd., UK. The devices digitise with a precision close to 5 μm and have an exceptionally high signal-to-noise ratio. The associated microelectronics were all custom made for the OPAL project. The detector began operation in 1991 and has since continued to be part of the OPAL experiment, performing to a very high standard and opening up new areas of physics studies.

The OPAL silicon strip microvertex detector with two coordinate readout

The OPAL experiment at the CERN LEP collider recently upgraded its silicon strip microvertex detector from one coordinate readout (φ only) to two coordinate readout (φ and z). This allows three dimensional vertex reconstruction and should improve lifetime measurements as well as b quark jet identification. This paper describes the new microvertex detector system with emphasis on the novel techniques and new components used to obtain the second coordinate information. These include the use of back-to-back single-sided detectors with orthogonally oriented readout strips, a gold printed circuit on a thin glass substrate to route the z strip signals to the electronics at the end of the detector, and the use of MX7 readout chips. Results on the performance of the new detector are presented.

Experimental Determination of the pi Meson Structure Functions by the Drell-Yan Mechanism

We have studied high statistics samples of dimuon events (∼35,000) produced from π± on platinum target in the mass interval 4.2≦Mμμ≦8.5 GeV at 150, 200 and 280 GeV/c. The π structure function is obtained by a fit ofd2σ/dx1dx2 to π+ and π− data. At 200 GeV, the simultaneous use of π+ and π− data allows a separate determination of the valence and sea structure functions of the π. Furthermore, the 150 and 280 GeV data allow an accurate determination of the shape of the valence structure function and give an estimate of its evolution betweenQ2=25 and 50 GeV2.

Evidence for ψψ production in π− interactions at 150 and 280 GeV/c

From the analysis of multimuon events produced by π− interactions at 150 and 280 GeV/c in the NA3 spectrometer, we present evidence for the production of two J/ψ mesons in the same interaction (13 events seen, for an expected background of about 0.2 events). Some possible production mechanisms are described and an estimation of the cross section is given.

Experimental cross section for dimuon production and the Drell-Yan model

Abstract We have measured the absolute cross section for dimuon production in hadron collisions at 200 GeV/c in the continuum region M = 4–8.5 GeV. In all the channels studied (pN, p N, π±N and π−H2) the experimental cross section is significantly larger by a factor of 2.3 ± 0.5 than expected from the Drell-Yan model. Furthermore, our proton-nucleon data allow a determination of the nucleon valence structure function which agrees with the deep inelastic lepton scattering data.

Measurement of the K−π− structure function ratio using the Drell-Yan process

Abstract The first measurement of the kaon to pion structure function ratio has beenperformed in a high integrated luminosity experiment studying the production of massive muon pairs. The ratio u K u π clearly deviates from 1 for values of x1 > 0.7. A theoretical model comparison is also briefly discussed.

ψψ production and limits on beauty meson production from 400 GeV/c protons

Abstract From a study of multimuon events obtained in a high luminosity proton-platinum experiment at 400 GeV/ c , we find 5 ± 4 ψψ events, which correspond to a production cross section σ ( ψψ = 27 ± 10 pb. The observed production is compared to the ψψ events previously found in the same apparatus from incoming π − ; a comparison with QCD predictions is performed, giving a good agreement with expectations from gluon-gluon fusion. Finally, using like-sign dimuon, trimuon and quadrimuon events, we give model-dependent upper limits on beauty meson production: 2 nb/nucleon for central models, 20 nb/nucleon for diffractive production.

Investigation of design parameters for radiation hard silicon microstrip detectors

Abstract In the context of the development of radiation hard silicon microstrip detectors for the CMS Tracker, we have investigated the dependence of interstrip and backplane capacitance as well as depletion and breakdown voltage on the design parameters and substrate characteristics of the devices. Measurements have been made for strip pitches between 60 and 240 μm and various strip implants and metal widths, using multi-geometry devices, fabricated on wafers of either 〈1 1 1〉 or 〈1 0 0〉 crystal orientation, of resistivities between 1 and 6 kΩ cm and of thicknesses between 300 and 410 μm . The effect of irradiation on properties of devices has been studied with 24 GeV /c protons up to a fluence of 4.3×10 14 cm −2 .

A large acceptance spectrometer to study high-mass muon pairs

Abstract This paper gives the outlines of the NA3 large acceptance magnetic spectrometer equipped with multiwire proportional chambers running at the CERN-SPS in an extensive study of the production of high mass muon pairs by hadronic beams. A special feature of this experiment is the powerful and efficient trigger and data acquisition system which allows operation of the spectrometer with intense beams, yielding at the same time low trigger rate and high proportion of good events. Some aspects of the off-line analysis program are also described.