New Perspectives for QCD Physics at the LHC

Journal Article · Wed Apr 27 00:00:00 EDT 2011 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.3579428· OSTI ID:1443103

Brodsky, S. J. ^[1]

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1. Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab; Southern Denmark Univ., Odense (Denmark). CP-Origins

I review a number of topics where conventional wisdom relevant to hadron physics at the LHC has been challenged. For example, the initial–state and final–state interactions of the quarks and gluons entering perturbative QCD hard–scattering subprocesses lead to the breakdown of traditional concepts of factorization and universality for transverse–momentum–dependent observables at leading twist. The soft–gluon rescattering effects, which are associated with the Wilson line of the propagating partons, also lead to Bjorken–scaling single–spin asymmetries, diffractive deep inelastic scattering, the breakdown of the Lam–Tung leading–twist relation in Drell–Yan reactions, as well as nuclear shadowing. The Gribov–Glauber theory applied to the antishadowing domain predicts that nuclear structure functions depend on the flavor quantum numbers of each quark and antiquark, thus explaining the anomalous nuclear dependence recently observed in deep–inelastic neutrino scattering. Surprisingly, isolated hadrons can be produced at large transverse momentum directly within a hard higher–twist QCD subprocess, rather than from jet fragmentation. The rate is predicted to be significant, even at the LHC. Such “direct” processes can explain the observed deviations from perturbative QCD predictions in measurements of inclusive hadron cross sections at fixed x_T = 2p_T/√s, as well as the “baryon anomaly”, the anomalously large proton–to–pion ratio seen in high centrality heavy–ion collisions at RHIC. The intrinsic charm contribution to the proton structure function at high x can explain the large rate for high p_T photon plus charm–jet events observed by D⁰ at the Tevatron. Intrinsic charm and bottom distributions also imply anomalously large production of charm and bottom jets at high p_T at the LHC, as well as a novel mechanism for Higgs and Z⁰ production at high x_F. Other novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates and the implications for the QCD contribution to the cosmological constant. Furthermore, the light–front wavefunctions derived in AdS/QCD can be used to calculate jet hadronization at the amplitude level. I also note that the elimination of the renormalization scale ambiguity for the QCD coupling using the scheme–independent BLM method will greatly improve the precision of QCD predictions and thus greatly increase the sensitivity of searches for new physics at the LHC.

• Research Organization: SLAC National Accelerator Lab., Menlo Park, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 1443103
• Report Number(s): SLAC-PUB-14303
• Journal Information: AIP Conference Proceedings, Vol. 1348, Issue 1; ISSN 0094-243X
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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