J.R. Hall

Differential cross sections and analysing powers for PP → π−π+ and K−K+ from 360 to 1550 MeV/c

Abstract Analysing powers and differential cross sections for p p → π − π + and p p → K − K + have been measured over the full angular range using a polarised target at LEAR at 20 beam momenta from 360 to 1550 MeV/c. Discrepancies in the normalisation of earlier d σ/ d Ω data at low momenta are clarified. Above 1000 MeV/c, A0N results confirm values close to +1 over most of the angular range for both reactions, in excellent agreement with earlier data of lower statistics. Below 1000 MeV/c, where the analysing power is measured for the first time, large variations of A0N with energy and angle are present.

p̄p total cross sections below 420 MeV/c

Abstract pp total cross sections have been measured from 220 to 413 MeV/ c in small (⩽ 10 MeV/ c ) steps of momentum with statistics of ± 0.5 %. There is no evidence for structure in the cross section, and a limit of 8 mb MeV/ c 2 is set with 90% confidence on the strength of any narrow resonance down to 250 MeV/ c .

Evidence against the S-meson

Abstract Measurements are reported of pp total cross sections from 388 to 599 MeV/c in small momentum steps. Statistical errors are typically ±0.4%and the normalisation uncertainty is ±0.7%. There is no evidence for the “S-meson”.

Asymmetry in p¯p elastic scattering

Abstract Asymmetries A 0 n have been measured at LEAR for s ¯ s elastic scattering for 15 beam momenta from 497 to 1550 MeV/ c .

Measurement of antiproton-proton small-angle elastic scattering at low momentum

Abstract Two high statistics measurements of antiproton-proton small-angle elastic scattering, at p = 233 MeV/c and p = 272 MeV/c, are presented. The measurements were carried out at the LEAR facility at CERN. By the Coulomb-nuclear interference method, values are obtained for the real-to-imaginary ratio ρ of the pp forward nuclear scattering amplitude and for its exponential slope b: ρ = + 0.041 ± 0.026 and b = 71.5 ± 4.5 (GeV/c)−2 at 233 MeV/c and ρ = −0.014 ± 0.027 and b = 47.7 ± 2.7 (GeV/c)−2 at 272 MeV/c. The method to derive these values is discussed in detail and so are the uncertainties contributing to their systematic error. The results are compared with predictions from forward dispersion relation calculations and with predictions from pp potential models.

Measurement of dσ/dΩ and Aon in pp elastic scattering between 497 and 1550 MeV/c

Measurements have been made of the differential cross section and asymmetry Aon for pp elastic scattering at 15 incident momenta between 497 MeV/c and 1550 MeV/c. The angular range where both particles have enough energy to traverse target and setup has been covered. The results are compared with predictions of various NN potential models. None of these models fully explains the present results, although the general trend of the data is predicted correctly.

Polarization at small angles in antiproton-carbon elastic scattering at LEAR energies

Abstract A double-scattering experiment of antiprotons on carbon has been carried out at the Low-Energy Antiproton Ring (LEAR) at CERN, to measure the polarization parameter A p C in antiproton-carbon elastic scattering at small angles. The polarization parameter has been inferred from the azimuthal distribution of the antiprotons after the second scattering. Data have also been collected with a liquid-hydrogen target as the second scatterer, thus allowing the sign of A p C to be determined. The experiment has been performed at two momenta of the extracted antiproton beam, 800 and 1100 MeV/c. A small positive value of the polarization has been observed, compatible with energy independence and a linear increase with the momentum transfer q. Parametrizing A p C as acq, we get ac = +0.72 0.10+0.09(GeV/c)−1. This result is compared with potential model predictions for NN amplitudes through a Glauber theory calculation.

Polarization at small angles in elastic pp and pC scattering at 550 MeV / c

Abstract Results are reported on the azimuthal asymmetry of antiprotons of ∼550 MeV / c , doubly scattered at small angles from protons and carbon. The measured asymmetries are small, statistically compatible with zero, and give polarization parameters smaller than those foreseen by some N N potential models.

First measurement of Donon in pp elastic scattering

Abstract The depolarization parameter D onon in p p elastic scattering has been measured at LEAR for thirteen momenta between 679 and 1550 MeV/c in the backward angular region. Striking disagreement with theoretical models is observed.

Real-to-imaginary ratio of the p̄p forward elastic scattering amplitude at 550, 757, and 1077 MeV/c

Abstract The ratio of the real to the imaginary part of the pp forward elastic-scattering amplitude ϱ has been measured at 550, 757, and 1077 MeV/c at LEAR, using the Coulomb-nuclear interference method. The results obtained for ρ and b, the nuclear slope, are ϱ = 0.084 ± 0.051 and b = 20.9 ± 2.1 (GeV/c)−2 at 550 MeV/c, ϱ = 0.102 ± 0.043 and b = 18.0 ± 0.5 (GeV/c)−2 = at 757 MeV/c, and ϱ = 0.059 ± 0.035 and b = 15.2 ± 0.3 (GeV/c)−2 at 1077 MeV/c.