Parton transverse momenta and quantum-chromodynamic effects in large-pThadron production

Abstract

Inclusive pion production at large transverse momenta in pp collisions is studied in the framework of partonparton scattering with partons carrying transverse momentum and with quark and giuon distributions determined from exact requirements of quantum chromodynamics. CERN ISR data are fairly well accounted for, but Fermilab data somewhat exceed the predictions. Gluon effects are considered in detail. * *K~~, K~~ has already been considered. We follow essentially the notation of Ref. 27, take wz, = m b = m , wzc=md = 0 , and s e t

Symmetric hadron pairs at large transverse momenta as a test of hard scattering models

“…Using the Buras and Gaemers parametrization [23], which has M~ (Q2 = 5 GeV2/c 2) smaller than that deduced from the new neutrino data, the gluon terms are smaller and we would predict a pair-cross section a factor two to three below the ~ + re--data. The importance of the quarkgluon term is, however, consistent with the analysis of the large PT single particle spectra [6][7][8][9][10].…”

“…In contrast to the phenomenological quark quark scattering model discussed in the preceding section, one assumes in the QCD approach the basic cross sections to be given by the lowest order perturbation theory [6][7][8][9][10]. In addition to the qq ~ qq subprocess one also includes contributions with gluons, qg ~ qg, qg ~ ~tg, gg ~ q(1, q?l ~ gg and gg ~ gg.…”

“…In Section IV the quantumchromodynamics model [6][7][8][9][10] is examined. Simple scale-breaking parametrizations of structure-and fragmentation functions are derived.…”

Azimuthal and single spin asymmetries in hard scattering processes

“…This term, once integrated over all k ⊥ 's, would be the only one in the factorization scheme in collinear configuration. It is also the only contribution considered in previous approaches using the parton model with TMD effects but neglecting the new spin and k ⊥ dependent, leading-twist, PDF's and FF's [227,228,229,230]. In fact, focusing here on the qq → qq channel, the additional contributions come from: a) The convolution of two (chiralodd) Boer-Mulders functions with the double transverse spin asymmetry for the qq interaction; 2) The convolution of one Boer-Mulders function and the Collins function (again, two chiral-odd quantities) coupled with the partonic spin-transfer factor.…”

Unintegrated parton distributions and pion production in pp collisions at RHIC energies

“…[3,4,5,7,8]) to jet and/or meson production to small transverse momenta it was proposed to add an extra Gaussian distribution in the transverse momentum of colliding partons [6,7,8,9,10,11,12]. In addition to assuming the parameter of the Gaussian distribution to be x-independent, one has to substitute t → t − µ 2 , u → u − µ 2 and s → s + 2µ 2 in order to avoid infinities in the matrix element squared contributing in this approach at finite transverse momenta.…”