O. E. Overseth

A study of inclusive Λ polarization from hydrogen and other targets at 28 GeV

Abstract We report measurements of inclusive Λ polarization, produced by unpolarized protons incident at several momenta (20, 24, and 28.5 GeV/ c ) onto hydrogen, deuterium, and beryllium targets. A large polarization from hydrogen, P = −0.34 ± 0.06 at p P T = 1.2 GeV/ c , establishes the fact that inclusive Λ polarization arises from p-p collisions.

Λ0 hyperon polarization in inclusive production by 24 GeV protons on platinum

Abstract We report a search for Λ 0 polarization in inclusive production by 24 GeV protons on platinum made on data taken at CERN. These data show Λ 0 polarization of the same direction and magnitude and with the same p T dependence as found at 300 GeV at Fermilab.

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.

Branching ratio and asymmetry for Xi 0--> Lambda gamma.

We have measured the branching ratio {Gamma}({Xi}{sup 0}{r arrow}{Lambda}{gamma})/{Gamma}({Xi}{sup 0}{r arrow}{Lambda}{pi}{sup 0}) to be (1.06{plus minus}0.12(stat){plus minus}0.11(syst)){times}10{sup {minus}3}. In 670 000 {Lambda}{gamma} candidates we found 116{plus minus}13 {Xi}{sup 0}{r arrow}{Lambda}{gamma} decays (background subtracted). These compare with 29 510 {Xi}{sup 0}{r arrow}{Lambda}{pi}{sup 0} events reconstructed from the {Lambda}{gamma}{gamma} sample. Monte Carlo studies gave the relative acceptances for the two processes. The helicity of the {Lambda} yielded the product of asymmetry parameters {alpha}({Lambda}{r arrow}{ital p}{pi}{sup {minus}}){alpha}({Xi}{sup 0}{r arrow}{Lambda}{gamma})=0.27{plus minus}0.28, which implies {alpha}({Xi}{sup 0}{r arrow}{Lambda}{gamma})=0.43{plus minus}0.44, where the uncertainty is all statistical.

The first measurement of the Ξ0 magnetic moment

Abstract The magnetic moment of the Ξ 0 hyperon has been measured to be μ Ξ 0 = −1.20 ± 0.06 μ N .

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.