Novel High Transverse Momentum Phenomena in Hadronic and Nuclear Collisions

TL;DR

This paper explores novel QCD phenomena at high transverse momentum in hadronic and nuclear collisions, explaining anomalies and correlations through direct processes, rescattering effects, and holographic wavefunctions.

Contribution

It introduces new phenomenological insights into high-p_T reactions, including direct higher-twist processes, rescattering effects, and applications of AdS/CFT to compute hadron wavefunctions.

Findings

Direct higher-twist processes explain the baryon anomaly at RHIC.

Rescattering interactions lead to observable single-spin asymmetries.

AdS/CFT provides analytic light-front wavefunctions for hadrons.

Abstract

I discuss a number of novel phenomenological features of QCD in high transverse momentum reactions. The presence of direct higher-twist processes, where a proton is produced directly in the hard subprocess, can explain the "baryon anomaly" -- the large proton-to-pion ratio seen at RHIC in high centrality heavy ion collisions. Direct hadronic processes can also account for the deviation from leading-twist PQCD scaling at fixed x_T = 2p_T/\sqrt s. I suggest that the "ridge" -- the same-side long-range rapidity correlation observed at RHIC in high centrality heavy ion collisions is due to the imprint of semihard DGLAP gluon radiation from initial-state partons which have transverse momenta biased toward the trigger. Rescattering interactions from gluon-exchange, normally neglected in the parton model, have a profound effect in QCD hard-scattering reactions, leading to leading-twist single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, the breakdown of the Lam-Tung relation in Drell-Yan reactions, nuclear shadowing --all leading-twist dynamics not incorporated in the light-front wavefunctions of the target computed in isolation. Antishadowing is shown to be quark flavor specific and thus different in charged and neutral deep inelastic lepton-nucleus scattering. I also discuss the consequences of color-octet intrinsic heavy quark distributions in the proton for heavy particle and Higgs production at high x_F. The AdS/CFT correspondence between Anti-de Sitter space and conformal gauge theories allows one to compute the analytic form of frame-independent light-front wavefunctions of mesons and baryons and to compute quark and gluon hadronization at the amplitude level.