We report the result of a brief experiment to measure the cross section for photoproduction of Jψ(3100). At a mean energy of 55 GeV we find this cross section per nucleon to be 37.5 ± 8.2 (statistical) ± 4 (systematic) nb. The result establishes the previously indicated rise in Jψ photoproduction on protons above 20 GeV and suggests that the rise has occurred by 55 GeV.
CROSS SECTION PER NUCLEON DERIVED FROM DEUTERIUM DATA ASSUMING INCOHERENT PART OF T DISTRIBUTION HAS EXPERIMENTAL SLOPE OF 1.8 +- 0.4 GEV**-2, 6 PCT COHERENT PART CALCULATED WITH KNOWN DEUTERIUM WAVE FUNCTION AND NEGLECTING SHADOWING. The mean P quoted in the table assumes the J/PSI energy equals the photon energy.
ρ± photoproduction from hydrogen and deuterium at 9.6 GeV is studied. The reactions γp→ρ+n and γp→ρ−Δ++(1236) have cross sections much larger than expected from pion exchange alone. t distributions do not show the sharp forward peak characteristic of one-pion exchange contributions. Density matrices indicate an isotropic decay distribution. The ratio of ρ+ to ρ− production on deuterium differs from unity and by the amount expected from interference between ρ and A2 exchanges. We conclude that π exchange is unimportant for ρ± photoproduction, and infer that ρ exchange dominates.
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DENSITY MATRICES IN HELICITY FRAME - UNPUBLISHED.
We have studied ω photoproduction using 7.5- to 10.5-GeV tagged photons. Cross sections from hydrogen lie 22% below the bubble chamber results of Ballam et al., but have a similar slope. Density matrices indicate approximate s-channel helicity conservation. The proton-neutron cross-section difference is midway between zero and the value suggested by the γp−γn total-cross-section difference. Fits to the cross sections for D, Be, and Cu and those for Be, C, Al, Cu, and Pb from a previous experiment yield σωN=25.4±2.7 mb and γω24π=7.6±1.2.
FORWARD CROSS SECTION IS 366 +- 49 MUB/GEV**2 AND SLOPE IS 47.1 +- 8.0 GEV**-2.
FORWARD CROSS SECTION IS 9.56 +- 1.24 MB/GEV**2 AND SLOPE IS 160 +- 23 GEV**-2.
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We observe a resonancelike structure in the total cross section for hadron production by e+e− colliding beams at a mass of 4414 ± 7 MeV having a total width Γ=33±10 MeV. From the area under this resonance, we deduce the partial width to electron pairs to be Γee=440±140 eV. Further structure of comparable width is present near 4.1 GeV.
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Measurements of the polarised beam asymmetry parameter Σ for eta photoproduction from protons, have been carried out at incident energies of 2.5 GeV and 3.0 GeV, and for various t -values between −0.2 (GeV/c) 2 and −1.2 (GeV/c) 2 . The values of Σ are close to +1 for values of | t | less than 0.7 (GeV/c) 2 , showing that there can be little contribution from unnatural parity exchange in any Regge exchange model of the process, in disagreement with present theories. Differential cross sections for the process werre also measured, and are consistent with those from other experiments.
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We derive cross-sections for the inclusive productiion in p̄p interactions at 100 GeV /c of π 0 , K S 0 and Λ 0 Λ 0 of 91.5±5.7 mb, 5.2±0.4 mb and 4.8±0.4 mb respectively, which are all higher than pp cross-sections at energy. We find indications that these differences can be attributed to “annihilation” processes.
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An experiment has been completed at the Daresbury synchrotron to measure the asymmetry in the photoproduction cross section of neutral pions on hydrogen, for photons polarised normal to and in the production plane. The source of polarised photons was coherent bremsstrahlung of electrons traversing the lattice structure of diamond and the polarisation P of the γ beam was calculated from the measured intensity of the coherent spike. The asymmetry parameter Σ, defined as Σ = ( σ ⊥ − σ |)/( σ ⊥ + σ |) where σ ⊥( σ |) are the cross sections for photons polarised perpendicular (parallel) to the production plane, has been measured over a range of photon energies from 1.2 to 2.8 GeV and over a range of − t (the square of the four-momentum transfer) from 0.13 (GeV/ c ) 2 to 1.4 (GeV/ c ) 2 . A marked energy variation in the value of Σ is found over the energy region 1.6–1.8 GeV.
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
The differential cross section for neutron-deuteron elastic scattering was measured for four-momentum transfers 0.3 < − t < 2.0 (GeV/c) 2 with incident neutron momenta between 6 and 12.5 GeV/c. The measurement was made with spark chambers at the Argonne ZGS. Results are compared with proton-deuteron elastic scattering at comparable energies as a test of isospin invariance in strong interactions and with the predictions of the Glauber multiple scattering theory. Very good agreement is found.
UNPUBLISHED DATA.
No description provided.
UNPUBLISHED DATA.
We have observed an azimuthal asymmetry in inclusive hadron production by e+e− annihilation at the center-of-mass energy s=7.4 GeV. The asymmetry is caused by the polarization of the circulating beams in the storage ring and allows separate determination of the transverse and longitudinal structure functions. We find that transverse production dominates for x>0.2 where x is the scaling variable 2ps.
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