We have measured differential cross sections for pion elastic scattering from H3 and He3 in the angular region near the minimum in the non-spin-flip amplitude. Data were acquired for incident pion energies of 180, 220, 256, and 295 MeV. Nuclear charge symmetry is investigated with the aid of several charge-symmetric ratios formed from combinations of measured cross sections. A particularly intriguing result is obtained from the superratio R, which is defined as R=dσ(π+3H)dσ(π−3H)/dσ(π+3He)dσ(π−3He). R is found to be greater than unity at 180 MeV and significantly smaller than unity at 256 MeV, with the transition occurring at around 210 MeV. The charge-symmetry prediction for this ratio (after allowance for the Coulomb force) is one, and is independent of energy and angle. © 1996 The American Physical Society.
Axis error includes +- 3/3 contribution.
Axis error includes +- 3/3 contribution.
Axis error includes +- 3/3 contribution.
Interest in the production of hyperon-antihyperon pairs following antiproton-proton annihilation stems largely from attempts to understand the nature of flavor production. To date the major focus of both the experimental and the theoretical effort has been on the p¯p→Λ¯Λ reaction. In this paper, we present data on the complementary channels p¯p→Σ¯0Λ and p¯p→Λ¯Σ0. Events from the kinematically similar p¯p→Λ¯Λ reaction were obtained in parallel. The procedure to distinguish these three separate reactions is described and results for all channels are presented. These include the total and differential cross sections, hyperon polarizations, and spin correlation coefficients. Data were obtained at incident antiproton lab momenta of 1.726 and 1.771 GeV/c which correspond to excess kinetic energies in the p¯p→Λ¯Σ0+c.c. reaction of 26 and 40 MeV, respectively, above threshold. Comparisons are made to earlier work at similar excess energies in the p¯p→Λ¯Λ channel. The low-energy regime has been highlighted in this experiment to reduce the complexity in the theoretical analysis. © 1996 The American Physical Society.
No description provided.
Axis error includes +- 2.3/2.3 contribution.
Axis error includes +- 2.3/2.3 contribution.
Inclusive π+ photoproduction below the Δ(1232) resonance has been measured from H, C, Ca, Sn, and Pb at laboratory angles of 51°, 81°, 109°, and 141° using tagged photons and ΔE-E plastic scintillator telescopes with 17-MeV thresholds. Particle identification involved both the determination of differential energy loss and the detection of the μ+ from the π+ decay. Double differential cross sections, angular distributions, and total cross sections were obtained for four incident photon energy bins centered at 184, 194, 204, and 213 MeV. Comparisons are made to both theoretical predictions and previous data sets. Ratios of nuclear cross sections to those obtained from the proton are extracted, and the features of these ratios are discussed. © 1996 The American Physical Society.
No description provided.
A search for direct electron pairs was performed at the 6.4 TeV 32 S emulsion interactions at CERN. A total of 81 directly produced electron pairs have been observed, with an average number per interaction of about two. The results have been analysed in the light of the predictions of quantum electrodynamical calculations. A simple interpretation for the extracted results based on the virtual mass distribution is presented. The experimental results are in partial agreement with the present theories. The virtual mass distribution does not show a 1/m behaviour.
No description provided.
No description provided.
The pp → ppη reaction has been measured at six energies close to threshold, from 1258 MeV to 1352 MeV, using an internal cluster gas jet target in the CELSIUS storage ring. The η is detected through its decay photons, in an array of CsI detectors, and the forward-going protons are detected in a plastic scintillator spectrometer. A complete event reconstruction is obtained at the higher energies in the measured interval. The new data, together with earlier data, give an accurate determination of the energy dependence close to threshold. The influence of the η-proton FSI is seen in the total cross section data as well as in a Dalitz plot of the η-p invariant mass distributions.
No description provided.
The probability of deuteron formation resulting from the interaction of high energy protons with nucleons, light nuclei (CNO) and heavy nuclei (Ag, Br) is discussed. The proportionality of the identified deuterons and protons (produced at the same angle due to the same interaction) agrees with that of the Butler and Pearson model which owes the deuteron formation to the average nuclear interaction seen by the cascade nucleons within the nucleus and then the normal n-p interaction. The data are based on the momentum and angular distributions of the outgoing particles.
No description provided.
Muon pair production is studied in p - W and S U collisions at 200 GeV per nucleon, as a function of transverse momentum P Tμμ . The inclusive ϱ + ω and Φ differential cross-sections dσ dP T are measured in the dimuon decay channel, for P T ≥ 0.6 GeV/c, in the central rapidity region, 3.0≤ y ≤ 4.0. Assuming the power law A-dependence σ = σ 0 ( A beam · A target ) α , the study of the integrated cross-sections for p - W and S U collisions leads to α ϱ + ω = 1.00±0.02±0.07 and α Φ = 1.23±0.03±0.05, showing clear evidence of Φ enhancement in S U interactions as compared to p - W collisions.
Statistical errors only.
Statistical errors only.
Statistical errors only.
The p̄p total annihilation cross section has been measured, with the Obelix apparatus at LEAR, at ten values of the antiproton incident momentum between 43 and 175 MeV/ c . The values of the cross section show that the well known 1 p behaviour of the annihilation cross section is drastically modified at very low momenta, which demonstrates the important role of the Coulomb force in low energy p̄p interaction. Moreover, they do not present any explicit resonant behaviour. Finally, when compared to potential model calculations, the data suggest that the percentage of P-wave in p̄p interaction around 50 MeV/ c antiproton incident momentum is less than 5%.
No description provided.
Antiproton production near midrapidity has been studied in central collisions of 32 S with sulphur, silver and gold nuclei at 200 GeV per nucleon. The measured transverse mass distributions can be described by an exponential with inverse slope parameters of about 200 MeV, similar to those obtained from Λ spectra. The rapidity density increases weakly with the target mass, ranging from 0.4 to 0.7. The ratio Λ p near midrapidity is approximately 1.4 on average, significantly larger than the corresponding ratio observed in proton-proton and proton-nucleus collisions.
No description provided.
No description provided.
Differential and total cross sections for the photoproduction of neutral pions from the proton have been measured for incident photon energies from 140–270 MeV, using the photon spectrometer TAPS at the tagged photon beam of the 855 MeV Mainz Microtron. The energy dependence of the s- and p-wave multipoles close to threshold was deduced from a multipole fit and a multipole analysis. The extracted s-wave amplitude E 0+ at threshold is found to be significantly smaller than the prediction of the classical low energy theorems, but is in reasonable agreement with the chiral perturbation theory.
No description provided.
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