MEASUREMENTS OF SINGLE DIFFRACTION AT ROOT-S=630GEV - EVIDENCE FOR A NONLINEAR ALPHA(T) OF THE POMERON

We report measurements of the inclusive differential cross section for the single-diffractive reactions p(i) + (p) over bar --> p(f) + X and p + <(p)over bar (i)> --> X + <(p)over bar (f)> at root s = 630 GeV, in the momentum transfer range 0.8 < -t < 2.0 GeV2 and final-state Fey nman-x(p) > 0.90. Based on the assumption of factorization, several ne w features of the pomeron flux factor are determined from simultaneous fits to our UA8 data and lower energy data from the CHLM collaboratio n at the CERN Intersecting Storage Rings. Prominent among these is tha t the effective pomeron Regge trajectory requires a term quadratic in t, with coefficient alpha '' = 0.079 +/- 0.012 GeV-4. We also show tha t the data require a pomeron-proton cross section that first decreases with increasing diffractive mass (corresponding to the PPR term in th e triple-Regge expansion) and then increases at larger mass (the PPP t erm), similar to real particle total cross sections. We measure the pr oduct K sigma(0) = 0.72+/-0.10 mb GeV-2 where K is the normalization c onstant of the pomeron flux factor in the proton and ao is the scale c onstant in the pomeron-proton total cross section. Finally, we report the occurrence of ''beam jets'' in the pomeron direction in the rest f rame of the diffractive system. (C) 1998 Elsevier Science B.V.