Edmond Craig Dukes

Direct photon production in proton-antiproton interactions at √s = 24.3 GeV

Abstract Direct photons have been studied in pp interactions at √s = 24.3 GeV and in the transverse momentum (pT) range 3–7 GeV/c(0.25

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.

Precise comparison of antiproton-proton and proton-proton forward elastic scattering at √s = 24.3 GeV

Abstract We report results from a measurement of antiproton-proton and proton-proton small-angle elastic scattering at √ s = 24.3 GeV in the range 0.001 ⩽ | t | ⩽ 0.06 (GeV/ c ) 2 . The measurement was performed at the CERN p p Collider by using silicon detectors to observe protons recoiling from a hydrogen cluster-jet target intercepting the stored p and p beams. Fits to the measured differential cross sections yield the ratio of the real to the imaginary part of the forward nuclear scattering amplitude ρ and the nuclear slope parameter b for both p p and pp. We find that the difference Δρ = ρ ( p p ) − ρ( pp ) = 0.031 ± 0.010 agrees with conventional fits and disagrees with the “odderon” fit designed to accommodate the recent UA4 measurement of ρ( p p) at 546 GeV.

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.

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.

Polarization of Σ0 hyperons in inclusive production from 28.5 GeV/c protons on beryllium

The polarization of Σ0 hyperons produced in an inclusive reactons hasbeen measured for the first time. From a sample of 11 000 events produced by 28.5 GeV/c ptorons in the reaction p+Be→Σ0+X, the Σ0 polarization has a value of +0.28±0.13 at pt=1.01 GeV/c and xf=0.60. The polarization of 53 000 Λ hyperons produced from 28.5 Gev/c protons inthe reaction p+Be→Λ+X has been measured in the kinematic range 0.64<pt<1.14 GeV/c and 0.42<xf<0.62. The average Λ polarization is found to be −0.188±0.024, consistent with previous results.

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.

Electron identification using a synchrotron radiation detector

Abstract A xenon filled multiwire proportional chamber was used to detect synchrotron radiation from high energy electrons traversing the field of a standard spectrometer magnet. Signals from the chamber were used to achieve an electron trigger with a pion rejection of ∼ 17 and an average electron detection efficiency of 81%. Off-line analysis of the chamber signals increased the pion rejection to 59 with an electron efficiency of 77%.

A lead/proportional-tube electromagnetic calorimeter for direct photon detection

Abstract The fine-grained lead/proportional-tube electromagnetic calorimeter used in CERN experiment UA6 is described. Test-beam results demonstrate linear energy response over a wide dynamic range, position resolution for shower localization reaching 1.7 mm for 70 GeV electrons, and good electron/hadron differentiation. Electron shower transverse widths are measured to be less than 9.0 mm for energies between 3 and 70 GeV. This feature allows us to identify neutral-meson decays yielding two close photon showers that constitute the main background to single-photon detection.