We report measurements of the inclusive differential cross section for the singlediffractive reactions: p i +p → p f + X and p +p i → X +p f at √ s = 630 GeV, in the momentum transfer range, 0.8 < −t < 2.0 GeV 2 and final state Feynmanx p > 0.90. Based on the assumption of factorization, several new features of the Pomeron Flux Factor are determined from simultaneous fits to our UA8 data and lower energy data from the CHLM collaboration at the CERN-Intersecting Storage Rings.Prominent among these is that the effective Pomeron Regge trajectory requires a term quadratic in t, with coefficient, α ′′ = 0.079±0.012 GeV −4 . We also show that the data require a Pomeron-proton cross section that first decreases with increasing diffractive mass (corresponding to the PPR term in the triple-Regge expansion) and then increases at larger mass (the PPP term), similar to real particle total cross sections. We measure the product, Kσ 0 = 0.72 ± 0.10 mb GeV −2 , where K is the normalization constant of the Pomeron Flux Factor in the proton and σ 0 is the scale constant in the Pomeron-proton total cross section. Finally, we report the occurence of "beam jets" in the Pomeron direction in the rest frame of the diffractive system.
Results are presented from a study of jet production in p p interactions with p s = 630 GeV at the CERN Sp pS-Collider, which are tagged by a proton or antiproton which possesses more than 90% of the incident beam momentum. The hard scattering which occurs between a parton in a beam particle and another in the soft residual component ( P omeron-dominated) of the tagged proton allows the Pomeron's partonic structure to be investigated. The observed jet distributions are in good agreement with expectations for hard parton-parton scattering in QCD. The Pomeron exhibits a hard structure like (1-x). However, there is an additional signicant (30%) -function-like component, in which the entire momentum of the Pomeron seems to participate in the hard scattering.
The UA8 experiment previously reported the observation of jets in diffractive events containing leading protons ("hard diffraction"), which was interpreted as evidence for the partonic structure of an exchanged Reggeon, believed to be the Pomeron. In the present Letter, we report the final UA8 hard-diffractive (jet) cross section results and their interpretation. After corrections, the fraction of single diffractive events with mass from 118 to 189 GeV that have two scattered partons, each with E T jet > 8 GeV, is in the range 0.002 to 0.003 (depending on x p ). We determine the product, f K, of the fraction by which the Pomeron's momentum sum rule is violated and the normalization constant of the Pomeron-Flux-Factor of the proton. For a pure gluonic-or a pure qq-Pomeron, respectively: f K = (0.30 ± 0.05 ± 0.09) and (0.56 ± 0.09 ± 0.17) GeV −2 .
We report results of inclusive measurements of Λ• s, produced in the forward direction at the SppS with √ s = 630 GeV, using the UA8 small angle Roman Pot spectrometers. These measurements cover the range in Feynman-x F and transverse momentum, 0.6 < x F < 1.0 and 0.4 < p t < 0.7 GeV, respectively. Within a systematic uncertainty of ±20% on the absolute cross section measurements, the results are indistinguishable from those made by some of us in two earlier experiments at the CERN Intersecting Storage Rings, with energies, √ s = 53 and 62 GeV. In the x F -range, 0.6-0.9, the absolute cross sections are lower by a factor of 2 to 3 than the predictions of the Lund model as embodied in the PYTHIA 5.6 and JETSET 7.3 Monte Carlo programs, indicating inadequacies in knowledge of the baryon fragmentation function. For the largest x F -range, 0.9-1.0, the measurements agree with the Monte Carlo predictions. We have measured the average Λ• polarization for our events and find (6 ± 12%), consistent with previous measurements at the ISR in the present region of x F -p t .
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