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 .
Error on SLOPE is statistical only.
Measured differential cross sections corrected for small-angle trigger efficiency and absorption losses. Statistical errors only.
Measured differential cross sections corrected for small-angle trigger efficiency and absorption losses. Statistical errors only.
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 p̄p 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 p̄p potential models.
The corrected cross section is the measured divided by the average folding correction given in the paper.
The corrected cross section is the measured divided by the average folding Correction given in the paper.
Fits to data use the value of total cross sections of 263 & 296 mb for 272 & 233 Mev respectively derived from the authors total cross sections measurement. ETA is the spin dependence parameter.
The cross section for the production of π+π− or K+K− pairs in γγ interactions is measured for mππ between 1.7 and 3.5 GeV/c2 and for two intervals of γγ center-of-mass scattering angle. Results are compared with predictions of a QCD model.
Data read off graph.
Data read off graph.
Qausi-elastic ω production by ep scattering in the kinematic region 0.3. < Q 2 < 1.4 GeV 2 and 1.7 < W < 2.8 GeV was studied using a streamer chamber at DESY. The production angular distribution for γ V p → ω p has a strong non-peripheral component for W < 2 GeV. The ω production cross section falls by a factor of 4 as W changes from 1.7 to 2.8 GeV. In contrast the cross section for ω production with | t | < 0.5 GeV 2 is W independent between 1.7 and 2.8 GeV and for W > 2.0 GeV consistent in both W and Q 2 dependence with the predictions of a model based on one-pion exchange and diffraction.
FOR ALL T-VALUES. THE GAMMA* P TOTAL CROSS SECTION WAS TAKEN FROM A FIT TO THE DATA OF S. STEIN ET AL., PR D12, 1884 (1975). 'PPD'.
'PPD'. PERIPHERAL OMEGA PRODUCTION.
No description provided.
The reaction γ V p → p π + π − was studied in the W , Q 2 region 1.3–2.8 GeV, 0.3–1.4 GeV 2 using the streamer chamber at DESY. A detailed analysis of rho production via γ V p→ ϱ 0 p is presented. Near threshold rho production has peripheral and non-peripheral contributions of comparable magnitude. At higher energies ( W > 2 GeV) the peripheral component is dominant. The Q 2 dependence of σ ( γ V p→ ϱ 0 p) follows that of the rho propagator as predicted by VDM. The slope of d σ /d t at 〈 Q 2 〉 = 0.4 and 0.8 GeV 2 is within errors equal to its value at Q 2 = 0. The overall shape of the ϱ 0 is t dependent as in photoproduction, but is independent of Q 2 . The decay angular distribution shows that longitudinal rhos dominate in the threshold region. At higher energies transverse rhos are dominant. Rho production by transverse photons proceeds almost exclusively by natural parity exchange, σ T N ⩾ (0.83 ± 0.06) σ T for 2.2 < W < 2.8 GeV. The s -channel helicity-flip amplitudes are small compared to non-flip amplitudes. The ratio R = σ L / σ T was determined assuming s -channel helicity conservation. We find R = ξ 2 Q 2 / M ϱ 2 with ξ 2 ≈ 0.4 for 〈 W 〉 = 2.45 GeV. Interference between rho production amplitudes from longitudinal and transverse photons is observed. With increasing energy the phase between the two amplitudes decreases. The observed features of rho electroproduction are consistent with a dominantly diffractive production mechanism for W > 2 GeV.
DIPION CHANNEL CROSS SECTION.
THE TOTAL CROSS SECTION WAS OBTAINED BY THE AUTHORS FROM A FIT TO THE SINGLE ARM DATA OF S. STEIN ET AL., PR D12, 1884 (1975).
No description provided.