P.T. Cox

The total neutral energy spectra in the central region of α−α, d−d and p−p interactions at sNN = 31 GeV per nucleon pair at the CERN ISR

The spectra in total neutral energy, ETOT0, have been measured in pp, dd and αα collisions at centre-of-mass energy per nucleon pair, sNN, of 31 GeV. The range in ETOT0 covered was 1 to 19 GeV in pp, 18 to 24 GeV in dd and 1 to 34 GeV in αα interactions. The ratio of the αα to the pp spectra rises monotonically from 7 at ETOT0 = 1.5 GeV to 105 at ETOT 0 = 19 GeV. Since ETOT0 is the sum over many particles in the detector, it is directly sensitive to multiple nucleon-nucleon collisions in the interacting α particles. The αα spectrum in the range 8 < ETOT0 < 17 GeV is consistent with being described by a simple model of 4 simultaneous nucleon-nucleon collisions with a cross section about equal to 10% of the observed αα interaction cross section. The spectrum of ETOT0 above 17 GeV is even flatter than this extreme case where four nucleon pairs are interacting.

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.

Three-jet events at the CERN intersecting storage rings

Three-jet events have been observed in pp collisions at s = 62.3 GeV. The data were collected using a total neutral energy trigger with a threshold at 25 GeV. These events appear predominantly as two jets, with some appearing as three jets. A novel analysis for the extraction of 2-jet and 3-jet events is described, and some of the event properties are discussed. The relative numbers of two- and three-jet events are studied within the framework of leading-order QCD, and yield a value of αs(K3/K2) = 0.19 ± 0.02 (stat.) ± 0.04 (syst.).

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.

\alpha_s

Abstract A comparison between p p and pp interactions at √s = 52.7 GeV is presented for a total neutral transverse energy (ETo) trigger and for a high transverse momentum (pT) neutral cluster trigger. The rate of production of events in the range 6 p p collisions than in pp collisions. A study of the structure of the events shows this excess to be due to more isotropic events being produced in p p collisions. The ratio of the production cross section for single neutral clusters in p p and pp interactions in the range 1.25

using direct photon production cross-sections in

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.