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.
Cross sections for ρ0 electroproduction measured in a streamer-chamber experiment are separated into elastic (ep→epρ0) and inelastic production channels. For the elastic channel, the total cross section and t dependence are presented. For the inelastic channel (1σ)dσdz, (1σ)dσdpT2, and a density matrix element are shown and compared to quark-parton-model predictions. The ratio of ρ0 to direct π0 production is found to be 2.0±0.5±0.3, where the first error is statistical, and the second error is systematic.
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We have extended our survey of the reaction γ+p→p+e++e− by collecting 20 000 additional e+e− pairs in the invariant-mass region 900<m<1500 MeV. The measured interference pattern shows two enhancements at mass values of 1097 and 1266 MeV. The parameters of those structure, when interpreted as vector mesons in the VDM framework, are given.
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The differential cross section of the reaction ( γ p → p φ ) has been measured in the t range 0 ⩽ t ⩽ 0.4 GeV 2 and for photon energies from 3.0 to 6.7 GeV. In particular for the small t region the measurement accuracy was better than 10%. We obtained for the slope parameter B in an exponential parametrization of the differential cross section d σ /d t = A e − Bt values of B ⋍ 6 ± 0.5 GeV −2 which are significantly larger than the slopes obtained by most other experiments at higher t values. This indicates a t dependence of B particularly in the small t region.
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We present experimental data on the K L 0 p → K S 0 p reaction between 4 and 14 GeV/ c in the range 0.1 ≲ | t | ≲ 2 GeV 2 . This experiment has been performed at the CERN PS, using spark chambers and a large aperture magnet. The results show a break of slope at t = −0.3 GeV 2 . The ω trajectory deduced from the data has an intercept α (0) = 0.5 and a slope α ′ = 0.88. A comparison with various models shows that the non-flip amplitude is dominant.
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For the first time, the line reversed reactions π + p→K + Σ + and K − p→ π − Σ + have been studied in the same apparatus. We present the differential cross sections and polarizations over a large t range and at two momenta, 7.0 and 10.1 GeV/ c . The differential cross sections as a function of t are shown for the first time to cross over. Going from the lower to the higher momentum, the differences in cross section between the two reactions diminish at low | t | by about a factor 2. We find large polarizations of opposite sign for the two reactions. The momentum dependence, presented in the form of α eff ( t ) for the t range 0 to −2 (GeV/ c ) 2 , is compared with the expectations from the K ∗ −K ∗∗ trajectory.
-TMIN = 0.0100 GEV**2.
-TMIN = -0.0087 GEV**2.
-TMIN = 0.0067 GEV**2.
We report measurements of the electroproduction of ϕ mesons from hydrogen at Q2 values of 0.23, 0.43, and 0.97 GeV2 with |t| varying from 0.125 to 1.3 GeV2 at each Q2 point. The data show no evidence for a Q2 dependence of the slope of the t distribution; the forward cross section falls with increasing Q2 as the square of the ϕ propagator; the decay angular distributions agree with the predictions of s-channel helicity conservation; and the ratio of the longitudinal to the transverse component increases linearly with Q2.
'DATA POINT ONE'.
'DATA POINT TWO'.
'DATA POINT THREE'. POOR STATISTICS - NOT IN PUBLISHED FIGURE.
The reactions K + p → K ∗+ (890) p , K + p → K ∗+ (1420) p and K + p → K 0 Δ ++ have been systematically studied for eleven incident momenta between 3.0 and 16.0 GeV/ c . Cross sections, differential cross sections and density matrix elements are presented. For K ∗ (890) production the contributions from natural and unnatural parity exchanges have also been separated into I = 0 and I = 1 components. Effective trajectories have been extracted in the case of natural parity exchange, and also for Δ ++ production.
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DATA AT NEIGHBOURING MOMENTA ARE GROUPED TOGETHER. THE RESONANCE PRODUCTION TOTAL CROSS SECTIONS ARE FITTED BY P**-N. THIS TABLE GIVES THE VALUES FOR EACH GROUP OF MOMENTA OF THE FITTED TOTAL CROSS SECTIONS WHICH ARE USED TO NORMALIZE THE DIFFERENTIAL CROSS SECTIONS.
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We have studied photoproduction using a 1 m streamer chamber at DESY and a tagged photon beam with an energy range of 1.6 GeV < E γ < 6.3 GeV. We analysed approximately 30 000 events and report topological, channel and resonance production cross sections for a large number of reactions with three and five outgoing charged particles.
CHANNEL CROSS SECTIONS FOR 3, 5 AND 7 PRONG REACTIONS.
'PARAMETRIZATION'.
'INTERFERENCE'.
A systematic analysis is presented on the reaction K + p → K ∗0 (890) Δ ++ for nine incident momenta between 4.6–16.0 GeV/ c . Cross sections, differential cross sections and vector meson single density matrix elements are given. As a function of energy, little if any change is observed in either the shapes of the differential cross sections or in the values of the density matrix elements. The data are interpreted in terms of current ideas on t -channel exchange mechanisms.
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