R. E. Breedon

Observation of jet structure in high transverse energy events at the CERN intersecting storage rings

Abstract The spectrum d N d E T 0 ( E T 0 = neutral transverse energy) has been measured with an electromagnetic calorimeter covering 90% of 2 π in azimuth. The measurement, performed in pp collisions at s = 62 GeV , covered the E T 0 range from 10 to 30 GeV. Evidence is presented that a large fraction of these events are jet-like, the fraction increasing with E T 0 .

A measurement of the inclusive π0 and η production cross sections at high pT in p̄p and pp collisions at s = 24.3 GeV

Abstract Inclusive π 0 and η production at large transverse momentum were studied in both pp and pp interactions at √ s = 24.3 GeV. The experiment was performed using an internal molecular hydrogen gas jet target in the CERN SPS collider. No significant differences between production in pp and pp were observed in the transverse momentum range 2.5 P T c .

Observation of KNO scaling in the neutral energy spectra from αα and pp collisions at ISR energies

Abstract Neutral transverse energy spectra in pp and αα interactions are analyzed in terms of the wounded nucleon model. Analysis of the αα spectrum by application of a multiple nucleon-nucleon collision mechanism is conveniently performed when a gamma distribution is used to represent the pp spectral shape. The wounded nucleon model provides a reasonable description of the αα spectrum for the first three orders of magnitude, but completly fails to account for the slope of the high energy tail of the distribution. However, the pp and αα spectra can both be fitted to the same gamma distribution when scaled by their respective mean values and thus exhibit KNO scaling.

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.

Direct photon production at the CERN ISR

Abstract A measurement of direct photon production in pp collisions at a center of mass energy ∝ s =63 GeV is reported. Arrays of lead-glass calorimeters and multiwire proportional chambers were used as photon detectors. Data are presented in the transverse momentum range from 4.5 to 10 GeV/ c and compared with QCD predictions. The event structure of this sample is compared with that of a set dominated by high transverse momentum π O s .

Jets in high transverse energy events at the CERN intersecting storage rings

Abstract Most events with high neutral transverse energy, ET0, produced in pp colisions at √s = 62.3 GeV, are jet-like. The evidence for this is presented, based on data collected using an electromagnetic calorimeter covering 90% of 2π in azimuth. The spectrum dN/dET0 has been measured over the ET0 range from 10 to 35 GeV. Properties of the observed jets are discussed.

High pT π0 production from αα and αp collisions at the CERN ISR

Abstract The invariant cross sections for π0 meson production in alpha—alpha and alpha—proton collisions at the ISR were meas- ured up to transverse momenta of 7 GeV c and 8 GeV c , respectively. These measurements are compared with π0 production in pp collisions at the same values of s / nucleon, and the variation of the nuclear A-dependence with pT is determined.

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.