Proton-Proton Interactions at 5.5 GeV/c

Abstract

This report is based on about 10 500 pp collision events produced in the 81-cm Saclay hydrogen bubble chamber at CERN. Cross-section values for the different identified final states and resonances are given. The isobars iV*i 2 38, iV*i42o, iV*i6is, N*i688, iV*i 9 2o, and iV* 2 360 were identified and their production crosssection values were found via a best-fit analysis of different invariant-rnass histograms. About 70% of the isobars are connected with the quasi-two-body reactions pp -> N*N and pp -»N*N*. The reaction pp -» nN*m${pTr + ) with a cross section of 3.25±0.16 mb was analyzed in terms of a peripheral absorption model, which was found to be in good agreement with the data. Various decay modes of the iV*i6i8 and iV*i688 isobars were observed and their branching ratios determined. The branching ratio of mr + to pTr + ir~ was found to be 0.77±0.45 for N* m8 and 0.67±0.40 for iV*i688-. The branching ratio of N* 12 3&(p7r + )T-to. pir + ir~ of iV*i 688 was estimated to be 0.74±0.14. Pion production turned out to be mainly due to decay of isobars. Production of meson resonances turned out to be less important; the reaction pp -»ppaP -> ppir + ir~7r° was identified with a cross-section value of 0.11 ±0.02 mb. Finally, the production of neutral strange particles with a cross section of 0.45±0.04 mb is descussed. Strong formation of F*i 3 s5 is observed.

ρ0Meson Production in thepp→ppπ+π−Reaction atBalestra1, Bedfer2, Bertini3 et al. 2002Phys. Rev. Lett.

“…The angular distributions for ω production at this beam energy and at the smaller excess energy ǫ = 0.173 GeV [17] show strong nucleonic contribution too, but also an additional isotropic component signaling the importance of the mesonic πρ → ω fusion [8]. It is also interesting to note, that the observed ratio of the total cross sections for ρ 0 and ω production R = σ(ρ 0 )/σ(ω) = 0.46 ± 0.12 is very similar to the ratio obtained at higher energy (ǫ = 1.14 GeV) R = 0.48 ± 0.13 [9] and seems to indicate similar scaling of the cross section with √ s for both mesons.…”

“…Unfortunately, the large ρ width Γ = 0.15 GeV/c 2 and a small cross section hampered up to now successful ρ 0 identification for excess energies above threshold ǫ ≤ 1.1 GeV [9]. In this letter, we report on the first measurement of the exclusive total and differential cross sections of the ρ 0 production in proton-proton reactions at ǫ = 0.33 GeV, measured at the SATURNE II facility at Saclay.…”

“…A further investigation of the remaining events shows that, as observed at higher energies [9], most two pion events originate from the pp → ∆ ++ pπ − channel. Figure 1 shows the acceptance corrected pπ + invariant mass distributions for events fulfilling the M inv pπ + π − > 1.6 GeV/c 2 condition discussed above.…”

Measurements of $$\pi ^\pm $$ π ± , K $$^\pm $$ ± , p and $${\bar{\text

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Abstract Measurements of inclusive spectra and mean multiplicities of π ± , K ± , p andp produced in inelastic p + p interactions at incident projectile momenta of 20,31,40, 80 and 158 GeV/c ( √ s = 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively) were performed at the CERN Super Proton Synchrotron using the large acceptance NA61/SHINE hadron spectrometer. Spectra are presented as function of rapidity and transverse momentum and are compared to predictions of current models.

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Threshold behavior of direct electron production in proton‐beryllium collisions

“…A COIJ;lparison with the energy dependence of heavier mesons is not feasible since the data is too meagre at. these low energies 14 • From bubble chamber data 15 we have computed the inclusive r.+ r.-production cross section at these low energies. Shown as the solid curve in Figure 3.…”