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

Abstract

Abstract. The inclusive cross section of hadron pairs produced back-to-back with large transverse momenta is examined in the parton model. It is shown quantitatively that this cross section is determined directly by the hard scattering subprocesses, without being influenced by the internal momentum of the constituents, even for transverse momenta of the order of 2-3 GeV/c. The predictions of the phenomenological quark-quark scattering model and of the quantum chromodynamics model for the back-to-back cross section are compared with recent Fermi-lab data. Predictions are made for the corresponding cross section at ISR-energies.

Correlation with large transverse momentum photons and the gluon structure function

“…However, the input values at g= 0 remain unchanged implying a gluon distribution proportional to (1-X) 3 at Q~ = 5 GeV 2. This hard gluon distribution is essential for the good agreement with the data on symmetric hadron pairs [16,17]. …”

“…The parametrizations for the structure and fragmentation functions utilized in the following calculations are described in detail in our previous paper on symmetric hadron pairs at large PT [16]. The results were compared with FNAL data and lead to a quite successful prediction for the production of n o pairs in the ISR energy range [17].…”

“…xG(x,g) Compared to the parametrization in [16] we have changed the coefficient of g in r/0 It is now 9/4 2" times the corresponding coefficient in the valence distribution. The behaviour for x > 0.6 is thereby improved.…”

“…Concerning the indirect photons we have approximated their contributions by taking the elastic quark-quark and quark gluon subprocesses and allowing the quark to fragment into a photo n with the following fragmentation function as derived in the leading logarithm approximation by Frazer and Gunion [27] 1.14 The procedure to obtain the corresponding cross sections is the same as in the case of hadron pairs [16]. Figure 5 shows the cross section Efla/d3p~.dxE for the process p + p ~ 7(PT) + h+ (XE) + X at ~ = 45 and 63 GeV.…”

“…Firstly, in the hard scattering model the two-particle cross section may be described by a much simpler picture than the single particle yield. This is due to the suppression of Fermi motion effects [16]. Secondly, the possible dominance of the direct term, g + q ~ ~ + q, gives a number of qualitative expectations for the kinematic and quantum number structure of the opposite side jet.…”