Results of a search for a predicted enhancement of several microbarns in the charm-photoproduction cross section just above threshold are reported. No charm decays were detected, from which an upper limit to the charm cross section of 94 nb (90% C.L.) at Eγ≃10 GeV was obtained. Upper limits in the range 270 to 450 nb were also obtained for the peak cross sections for threshold enhancements in γp→D−Σc++ and similar channels.
UPPER LIMIT TO AVERAGE CHARM CROSS SECTION.
UPPER LIMITS TO INDIVIDUAL CHANNELS.
Production of the p p π + π − final state by two-photon scattering was observed. The cross section for γγ→p p π + π − was determined assuming phase space production. No evidence was found for the production or formation of resonances. Upper limits are given for Λ and Δ pair production, for production of p p ϱ 0 and for the two-photon excitation of c c bound states.
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Exclusive production of proton-antiproton pairs by two photon scattering at CM energies between 2.0 GeV and 3.1 GeV has been measured with the TASSO detector at the e + e − storage ring PETRA. The angular distribution is flat within the accepted CM angular range | cos Θ ∗ |⩽0.7 . The integrated cross section (| cos Θ ∗ |⩽0.6) drops from about 4 nb at 2 GeV to less than 0.5 nb above 3 GeV. For the two-photon production of the η c (2984) and its subsequent decay into proton-antiproton the upper limit Γ(η c →γγ)· B (η c → p p )<0.32 keV (95% CL) is found.
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UPPER LIMIT FOR THE PRODUCT OF THE ETA/C --> GAMMA GAMMA WIDTH AND THE BRANCHING RATIO OF ETA/C --> P AP IS DETERMINED TO BE 0.32 KEV WITH 90 PCT CL.
Production of proton-antiproton pairs by two-photon scattering has been observed at the electron-position storage ring PETRA. A total of eight proton-antiproton pairs have been identified using the time-of-flight technique. We have measured a total cross section of 4.5 ± 0.8 nb in the photon-photon c.m. energy range 2.0–2.6 GeV.
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Additional systematic uncertainty 25% not included.
We have measured the asymmetry parameter A and the spin correlation parameter A nn in pp elastic scattering, using the Argonne ZGS polarized proton beam and a polarized proton target. Angular distributions of A and A nn for | t | ≳ 0.2 (GeV/ c ) 2 were obtained at eight momenta between 1.10 and 2 if 2.75 GeV/ c . We find significant structure in both the energy and t -dependence of A nn at these energies. At p lab ≈ 1.34 GeV/ c A nn reaches a very large value of about 0.8–0.9 near θ cm = 90°.
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We present evidence for δ production in the reactions K − p→ Σ (1385) + δ − ; δ − → η 0 π − , and K − p → Λδ + π − ; δ + → η 0 π + , in a bubble chamber experiment with beam momentum in the range 3.1 to 3.6 GeV/ c . The η 0 from the δ decay is seen both as a missing mass effect, and in its charged decay modes. The δ − has a mass of 989 ± 4 MeV, and width a of 16 −16 +25 MeV (after allowing for experimental resolution). The cross section for Σ(1385) − δ − production is 7±3 μ b; the reaction is produced at small momentum transfers. The mass and width of the δ + are consistent with those of the δ − , and the cross section for the Λ 0 π − δ + final state is about 5 μb. Neither δ appears to be produced as a result of D 0 decay.
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In a study of the missing-mass spectrum near 1 GeV in the reaction π−+p→MM+n at three incident momenta near 2 GeV, we find no evidence for the recently reported narrow neutral mesons at 940, 963, and 1033 MeV.
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