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FastNLO: Fast pQCD calculations for PDF fits

Description: We present a method for very fast repeated computations of higher-order cross sections in hadron-induced processes for arbitrary parton density functions. A full implementation of the method for computations of jet cross sections in Deep-Inelastic Scattering and in Hadron-Hadron Collisions is offered by the ''fastNLO'' project.
Date: September 1, 2006
Creator: Kluge, T.; /DESY; Rabbertz, K.; U., /Karlsruhe; Wobisch, M. & /Fermilab
Partner: UNT Libraries Government Documents Department

Reggeon Non_Factorizability and Fixed Pole in DVCS

Description: We argue that deeply virtual Compton scattering will display Regge behavior {nu}{sub R}{sup {alpha}}(t) at high energy at fixed-t, even at high photon virtuality, not necessarily conventional scaling. A way to see this is to track the Reggeon contributions to quark-nucleon scattering and notice that the resulting Generalized Parton Distributions would have divergent behavior at the break-points. In addition, we show that the direct two-photon to quark coupling will be accessible at large t where it dominates the DVCS amplitude for large energies. This contribution, the J = 0 fixed-pole, should be part of the future DVCS experimental programs at Jlab or LHeC.
Date: August 3, 2009
Creator: Brodsky, Stanley J.; Llanes-Estrada, Felipe J.; Londergan, J.Timothy & Szczepaniak, Adam P.
Partner: UNT Libraries Government Documents Department

The Two-loop Anomalous Dimension Matrix for Soft Gluon Exchange

Description: The resummation of soft gluon exchange for QCD hard scattering requires a matrix of anomalous dimensions. We compute this matrix directly for arbitrary 2 {yields} n massless processes for the first time at two loops. Using color generator notation, we show that it is proportional to the one-loop matrix. This result reproduces all pole terms in dimensional regularization of the explicit calculations of massless 2 {yields} 2 amplitudes in the literature, and it predicts all poles at next-to-leading order in any 2 {yields} n process that has been computed at next-to-leading order. The proportionality of the one- and two-loop matrices makes possible the resummation in closed form of the next-to-next-to-leading logarithms and poles in dimensional regularization for the 2 {yields} n processes.
Date: June 27, 2006
Creator: Aybat, S.Mert; Dixon, Lance J. & Sterman, George
Partner: UNT Libraries Government Documents Department

Oddballs and a Low Odderon Intercept

Description: The authors report an odderon Regge trajectory emerging from a field theoretical Coulomb gauge QCD model for the odd signature J{sup PC} (P = C = -1) glueball states (oddballs). The trajectory intercept is clearly smaller than the pomeron and even the {omega} trajectory's intercept which provides an explanation for the nonobservation of the odderon in high energy scattering data. To further support this result we compare to glueball lattice data and also perform calculations with an alternative model based upon an exact Hamiltonian diagonalization for three constituent gluons.
Date: July 27, 2005
Creator: Llanes-Estrada, Felipe J.; U., /Madrid; Bicudo, Pedro; /Lisbon U. /Lisbon, IST; Cotanch, Stephen R. & U., /North Carolina State
Partner: UNT Libraries Government Documents Department

Large x Physics

Description: The large x{sub bj} domain of deep inelastic lepton-proton scattering provides essential information on the structure of the proton when the struck quark is far off-shell and one must take into account inter-quark correlations, higher twist effects, and the breakdown of standard DGLAP evolution. I briefly review predictions from PQCD and AdS/CFT. I also discuss how intrinsic heavy quark Fock states lead to novel production mechanisms for heavy hadrons.
Date: June 30, 2005
Creator: Brodsky, Stanley J.
Partner: UNT Libraries Government Documents Department

Twenty years of diffraction at the Tevatron

Description: Results on diffractive particle interactions from the Fermilab Tevatron {bar p}p collider are placed in perspective through a QCD inspired phenomenological approach, which exploits scaling and factorization properties observed in data. The results discussed are those obtained by the CDF Collaboration from a comprehensive set of single, double, and multigap soft and hard diffraction processes studied during the twenty year period since 1985, when the CDF diffractive program was proposed and the first Blois Workshop was held.
Date: October 1, 2005
Creator: Goulianos, K. & U., /Rockefeller
Partner: UNT Libraries Government Documents Department

Matter Dependence of the Three-Loop Soft Anomalous Dimension Matrix

Description: The resummation of soft gluon exchange for QCD hard scattering requires a matrix of anomalous dimensions, which has been computed through two loops. The two-loop matrix is proportional to the one-loop matrix. Recently there have been proposals that this proportionality extends to higher loops. One can test such proposals by computing the dependence of this matrix on the matter content in a generic gauge theory. It is shown that for the matter-dependent part the proportionality extends to three loops for arbitrary massless processes.
Date: January 23, 2009
Creator: Dixon, Lance J.
Partner: UNT Libraries Government Documents Department

Novel QCD Phenomena at Electron-Proton Colliders

Description: I discuss several novel phenomenological features of QCD which are observable in deep inelastic lepton-nucleon and lepton-nucleus scattering. Initial- and final-state interactions from gluon exchange, normally neglected in the parton model, have a profound effect on QCD hard-scattering reactions, leading to leading-twist single-spin asymmetries, the diffractive contribution to deep inelastic scattering, and the breakdown of the pQCD Lam-Tung relation in Drell-Yan reactions. Leading-twist diffractive processes in turn lead to nuclear shadowing and non-universal antishadowing--physics not incorporated in the light-front wavefunctions of the nucleus computed in isolation.
Date: July 25, 2008
Creator: Brodsky, Stanley J. & /SLAC /Durham U., IPPP
Partner: UNT Libraries Government Documents Department

Evidence for the Absence of Gluon Orbital Angular Momentum in the Nucleon

Description: The Sivers mechanism for the single-spin asymmetry in unpolarized lepton scattering from a transversely polarized nucleon is driven by the orbital angular momentum carried by its quark and gluon constituents, combined with QCD final-state interactions. Both quark and gluon mechanisms can generate such a single-spin asymmetry, though only the quark mechanism can explain the small single-spin asymmetry measured by the COMPASS collaboration on the deuteron, suggesting the gluon mechanism is small relative to the quark mechanism. We detail empirical studies through which the gluon and quark orbital angular momentum contributions, quark-flavor by quark-flavor, can be elucidated.
Date: August 23, 2006
Creator: Brodsky, S. J. & Gardner, S.
Partner: UNT Libraries Government Documents Department

Deep Inelastic Scattering at the Amplitude Level

Description: The deep inelastic lepton scattering and deeply virtual Compton scattering cross sections can be interpreted in terms of the fundamental wavefunctions defined by the light-front Fock expansion, thus allowing tests of QCD at the amplitude level. The AdS/CFT correspondence between gauge theory and string theory provides remarkable new insights into QCD, including a model for hadronic wavefunctions which display conformal scaling at short distances and color confinement at large distances.
Date: August 4, 2005
Creator: Brodsky, Stanley J.
Partner: UNT Libraries Government Documents Department