A. A. Carter

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.

Double parton scattering inpp collisions at\(\sqrt s = 63\) GeV

AbstractIn a study ofpp collisions at

The total cross-sections for pion-proton scattering between 70 mev and 290 mev

\sqrt s = 63

The extended OPAL silicon strip microvertex detector

GeV with more than 29 GeV total transverse energy emitted into 1.8 units of rapidity in the central region, we have extracted a sample of 4-jet events and compared it with models of the two sources of 4-jet production: double bremsstrahlung and double parton scattering. The data cannot be described by bremsstrahlung alone, and we extract the fraction of 4-jet events attributed to double parton scattering for various definitions of the 4-jet sample. We determine the double parton scattering/2-jet yield ratio, and this leads to a determination of the proton radius. We discuss the implications of our observations for the general understanding of high-ΣET events.

πp elastic scattering from 88 to 292 MeV

Abstract Phase shift solutions are presented at pion kinetic energies from 88 to 292 MeV where new measurements of the differential elastic cross section are available, and at 310 MeV. The resulting phase shifts are fitted to effective-range formulae. The resonant P 33 phase shift is allowed to take different values for π + p and π − p scattering. There are differences in mass and width between these charge states of the resonance of M 0 − M ++ = 1.4 ± 0.4 MeV/ c 2 and Γ 0 − Γ ++ = 10.3 ± 1.3 MeV/ c 2 . The difference in width can be accounted for largely but not entirely by the Coulomb barrier, the channel π − p → γ n, and the difference in phase space between π − p → π 0 n and π + p → π + p.

A search for glueballs and a study of doouble pomeron exchange at the CERN intersecting storage rings

Abstract Measurements have been made of the π∓ proton total cross sections over the laboratory kinetic energy range 70 to 290 MeV. The absolute accuracy of the data is generally 0.5 %, but decreases to 1 % for some points where applied corrections are large or where low particle fluxes limit the statistical accuracy. The parameters of the Δ0, Δ++ resonance have been calculated, and a discussion is included on the limitations placed by Coulomb barrier effects on extracting the basic nuclear phase shifts from data in this energy region.

The evaporative cooling system for the ATLAS inner detector

Abstract From fixed t dispersion relations we have obtained more accurate values for the pion nucleon coupling constant and s -wave scattering lengths, using our recent low energy πN angular distribution and total cross section data. The results are: f 2 = 0.0790 ± 0.0010, a 1 − a 3 = 0.262 ± 0.004 μ −1 , a 1 + 2 a 3 = − 0.014 ± 0.005 μ −1 .

Evidence for mesons with spins 3, 4 and 5 in pp → π−π+ in the mass region 2020 to 2580 MeV/c2

Abstract The OPAL experiment at the CERN LEP collider recently increased the geometrical acceptance of its silicon microvertex detector. The azimuthal coverage is improved by adding one pair of detector modules to each of the two layers, while the polar angle coverage is extended by adding new detector modules in line with the existing ones. This improves the efficiency for high quality tracking in OPAL and in particular for b quark tagging in Higgs boson searches. A description of the detector is given, with emphasis on new or modified elements with respect to the earlier version. Results on the performance of the new detector are presented.