1711The production of high-Pr particles in photon-induced reactions can be used as a probe of the rich QCD structure of a photon as well as of the short distance dynamics of hadron collisions. \Ve calculate the cross sections for high-Pr photons and pions produced in rP collisions to the lowest-order in QCD perturbation theory, taking account of the effects due to scaling violation in parton distribution and fragmentation functions. vVe fmc! that the contributions from different components of photons are equally important at relatively small Pr, (e.g., PrC:::lO Ge V / c at y'sc:::100 Gc V). At large Pr, however, the contributions from the subprocesses :with direct photon coupling dominate. Thus in the large-Pr region, inelastic Compton scattering, in which the rq---'Trq subprocess is dominant, provides us with a test of the shape of the quark propagator as well as of the quark charge. § 1. Introduction It has been suggested by a number of authors that high-transverse momentum processes are described within the framework of quantum chromodynamics (QCD) .D~6l Their analyses are based on the hard-collision model; high-transverse momentum particles are produced by a single hard collision between partons (quarks and gluons) of the incident particles. Meanwhile it is proven 7 l that the QCD corrections on the naive hard-collision model result in the following substitutions; all the scaling parton distribution-and fragmentation-functions with corresponding QCD scale-breaking counter parts, the coupling constants in the partonsubprocesses with the running coupling constants.As was first shown by Witten,SJ,g) photon structure functions consist, at least to the leading-logarithmic order, of two components; an exactly calculable "perturbative component" (second terms in Eqs.(2) and (3) below) and a "hadronic component" (third terms). At large Q 2 , the former grows like ln Q 2 and dominates, except at very small x, over the latter which behaves just like the hadron structure functions. A photon can also participate much more directly in subprocesses than a hadron, clue to a point-like coupling of the photon to a quark. (This is represented by the first terms in Eqs.(2) and (3) below.) Thus the study of the processes involving real photons is of considerable interest in revealing such three-fold structure of the photon, in probing rather directly the constituent subprocesses and in testing QCD perturbation theory.The purpose of the present paper is to carry out the calculation of the single-at North Dakota State University on June 2, 2015 http://ptp.oxfordjournals.org/ Downloaded from ** 1 Although the behaviour of Gal¢ is probably quite different from that of Ga1,o, this assumption is allowed because of the smallness of at North Dakota State University on June 2, 2015 http://ptp.oxfordjournals.org/ Downloaded from
Inclusive r and 71° productions at large Pr in rP collisions are studied in the framework of QCD hard-scattering model, by taking the parton transverse momenta into account. The re8ults are in good agreement with available data for a 21 GeV bremsstrahlung beam.
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