The dissociation of virtual photons, $\gamma^{\star} p \to X p$, in events with a large rapidity gap between $X$ and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities $Q^2>2$ GeV$^2$ and $\gamma^{\star} p$ centre-of-mass energies $40<W<240$ GeV, with $M_X>2$ GeV, where $M_X$ is the mass of the hadronic final state, $X$. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of $t$, the squared four-momentum transfer at the proton vertex and $\Phi$, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of $Q^2$ and $\xpom$, the fraction of the proton's momentum carried by the diffractive exchange, as well as $\beta$, the Bjorken variable defined with respect to the diffractive exchange.
The differential cross section DSIG/DT for the LRG and the LPS data samples.
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
We report measurements from elastic photoproduction of ω's on hydrogen for photon energies between 60 and 225 GeV, elastic φ photoproduction on hydrogen between 35 and 165 GeV and on deuterium between 45 and 85 GeV, elastic photoproduction on deuterium of an enhancement at 1.72 GeV/c2 decaying into K+K−, and elastic and inelastic photoproduction on deuterium of pp¯ pairs.
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The reaction K−p→K¯0π−p has been studied at 100 and 175 GeV/c and the reaction π−p→K0K−p at 50, 100, and 175 GeV/c. Both reactions are dominated by production of resonances, K*(890), K*(1430) and A2(1320), A2(2040), respectively. Production cross sections, t distributions, and decay-angular distributions are studied. Isoscalar natural-parity exchange is dominant. The energy dependence of the K* and A2 resonance production between 10 and 175 GeV/c is well described by a Regge-pole model. Our data on A2 corrects that in an earlier paper.
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The reaction π−p→K0K−p has been measured from 50 to 175 GeV/c. The production characteristics of the A2 have been analyzed. We find spin and t dependence similar to lower energies, but the cross section falls rapidly with energy. In a Regge description of π−p→A2−p our data imply a rather small Pomeron-exchange component.
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RAW CROSS SECTION WITHIN MASS CUTS.
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Virtual photoproduction of J/ ψ mesons has been measured for 280 GeV muon iron interactions in an iron/scintillator calorimeter target. The J/ψ's were identified by their decay into muon pairs. 315 events were observed, about half of which were elastic. The t , Q 2 and v distributions of these elastic events are presented. The v dependence is measured between 40 and 180 Mev and compared with lower energy photoproduction results. The Q 2 dependence is compared with the predictions of the vector dominance model.
TPRIME DISTRIBUTION OF ELASTIC J/PSI EVENTS FOR ALL Q2 AND NU WITH 280 GEV MUON BEAM.
NORMALIZED Q**2 DISTRIBUTION OF ELASTIC J/PSI EVENTS FOR ALL NU AND T WITH 280 GEV MUON BEAM.
EXTRAPOLATION OF Q**2 AND T DEPENDENCE TO CALCULATE D(SIG)/DT AT Q**2=0 AND T=0 FOR ELASTIC J/PSI PHOTOPRODUCTION PER NUCLEON.
Elastic ω-meson photoproduction on protons has been measured from 46 to 180 GeV. The cross section is approximately constant with photon energy and averages 1.10 ± 0.08 μb. The t dependence of the differential cross section is consistent with A exp(bt), where b=8.4±0.7 GeV−2. The photon-omega coupling constant, obtained from a normalization of hadron elastic-scattering cross sections to the photoproduction data of this experiment (with use of vector-meson dominance and an additive quark model), is γω24π=5.4±0.4.
THE QUOTED STATISTICAL ERRORS INCLUDE THE UNCERTAINTY IN THE CORRECTION FOR INELASTIC EVENTS. AVERAGE CROSS SECTION IS 1.10 +- 0.08 MUB.
EXPONENTIAL FIT TO DIFFERENTIAL CROSS SECTION.
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A thin polyethylene target was exposed to the internal proton beam of the Serpukhov accelerator at 30, 50, and 70 GeV. The wide-angle recoil protons were registered by photoemulsion stacks and the differential cross sections of the elastic p−p scattering in the range of four-momentum transfer squared 0.0025≤|t|≤0.12 (GeV/c)2 were measured. The ratio of the real to the imaginary part of the forward nuclear amplitude α, the slope parameter of the diffraction peak b, and the total elastic cross section σel were found to be as follows: at 30 GeV, α=−0.183±0.051, b=10.61±0.27 (GeV/c)−2, σel=7.7±0.2 mb; at 50 GeV, α=−0.068±0.040, b=11.25±0.28 (GeV/c)−2, σel=7.0±0.2 mb; at 70 GeV, α=−0.104±0.065, b=11.21±0.40 (GeV/c)−2, σel=7.1±0.2 mb.
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The differential cross sections for the elastic scattering of π+, π−, K+, K−, p, and p¯ on protons have been measured in the t interval -0.04 to -0.75 GeV2 at five momenta: 50, 70, 100, 140, and 175 GeV/c. The t distributions have been parametrized by the quadratic exponential form dσdt=Aexp(B|t|+C|t|2) and the energy dependence has been described in terms of a single-pole Regge model. The pp and K+p diffraction peaks are found to shrink with α′∼0.20 and ∼0.15 GeV−2, respectively. The p¯p diffraction peak is antishrinking while π±p and K−p are relatively energy-independent. Total elastic cross sections are calculated by integrating the differential cross sections. The rapid decline in σel observed at low energies has stopped and all six reactions approach relatively constant values of σel. The ratio of σelσtot approaches a constant value for all six reactions by 100 GeV, consistent with the predictions of the geometric-scaling hypothesis. This ratio is ∼0.18 for pp and p¯p, and ∼0.12-0.14 for π±p and K±p. A crossover is observed between K+p and K−p scattering at |t|∼0.19 GeV2, and between pp and p¯p at |t|∼0.11 GeV2. Inversion of the cross sections into impact-parameter space shows that protons are quite transparent to mesons even in head-on collisions. The probability for a meson to pass through a proton head-on without interaction inelastically is ∼20% while it is only ∼6% for an incident proton or antiproton. Finally, the results are compared with various quark-model predictions.
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Measurements on the reaction π−p→ηn have been carried out at Fermilab with beam energies from 20 to 200 GeV in the same experiment in which pion charge-exchange scattering was studied. The differential cross sections have a pronounced dip in the forward direction. The data can be described well by a simple Regge-pole model but the resulting A2 trajectory is not degenerate with the ρ trajectory extracted from the charge-exchange data.
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
We report on a study of pion charge-exchange scattering carried out at Fermilab in the energy range 20 to 200 GeV. The results can be described remarkably well by a simple Regge-pole model. The charge-exchange cross sections in the forward direction lead to a prediction for the difference in total cross sections of π−p and π+p which is in satisfactory agreement with direct measurements of this difference in another experiment at Fermilab.
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
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