Evidence for Parton kT Effects in High pT Particle Production

TL;DR

This paper presents measurements of high pT pi0 and photon production in proton and pion collisions, providing evidence that initial-state parton transverse momentum (kT) significantly influences the observed cross sections, and that including kT effects improves theoretical predictions.

Contribution

It offers experimental evidence for parton kT effects in high pT particle production and demonstrates that phenomenological inclusion of kT improves QCD calculations.

Findings

Data shows significant initial-state parton kT effects.

Inclusion of kT effects improves agreement with data.

Evidence supports the importance of parton transverse momentum in high pT processes.

Abstract

Inclusive pizero and direct-photon cross sections in the kinematic range 3.5 < pT < 12 GeV/c with central rapidities are presented for 530 and 800 GeV/c proton beams and a 515 GeV/c pi- beam incident on beryllium targets. Current Next-to-Leading-Order perturbative QCD calculations fail to adequately describe the data for conventional choices of scales. Kinematic distributions from these hard scattering events provide evidence that the interacting partons carry significant initial-state parton transverse momentum (kT). Incorporating these kT effects phenomenologically greatly improves the agreement between calculations and the measured cross sections.