M. Derrick et al., INCLUSIVE TRANSVERSE-MOMENTUM DISTRIBUTIONS OF CHARGED-PARTICLES IN DIFFRACTIVE AND NON-DIFFRACTIVE PHOTOPRODUCTION AT HERA, Zeitschrift fur Physik. C, Particles and fields, 67(2), 1995, pp. 227-237
Inclusive transverse momentum spectra of charged particles in photopro
duction events in the laboratory pseudorapidity range -1.2 < eta < 1.4
have been measured up to P-T = 8 GeV using the ZEUS detector. Diffrac
tive and non-diffractive reactions have been selected with an average
gamma p centre of mass (c.m.) energy of (W) = 180 GeV. For diffractive
reactions, the p(T) spectra of the photon dissociation events have be
en measured in two intervals of the dissociated photon mass with mean
values (M(X)) = 5 GeV and 10 GeV. The inclusive transverse momentum sp
ectra fall exponentially in the low p(T) region. The non-diffractive d
ata p show a pronounced high p(T) tail departing from the exponential
shape. The p(T) distributions are compared to lower energy photoproduc
tion data and to hadron-hadron collisions at a similar c.m. energy. Th
e data are also compared to the results of a next-to-leading order QCD
calculation.