Parton

About: Parton is a research topic. Over the lifetime, 13484 publications have been published within this topic receiving 368877 citations.

Charm quark and D * ± cross sections in deeply inelastic scattering at DESY HERA

Abstract: A next-to-leading order Monte Carlo program for the calculation of heavy quark cross sections in deeply inelastic scattering is described. Concentrating on charm quark and ${D}^{*\ifmmode\pm\else\textpm\fi{}}(2010)$ production at DESY HERA, several distributions are presented and their variation with respect to charm quark mass, parton distribution set, and renormalization or factorization scale is studied.

Modeling heavy ion collisions in AdS/CFT

Abstract: We construct a model of high energy heavy ion collisions as two ultrarelativistic shock waves colliding in AdS5. We point out that shock waves corresponding to physical energy-momentum tensors of the nuclei completely stop almost immediately after the collision in AdS5, which, on the field theory side, corresponds to complete nuclear stopping due to strong coupling effects, likely leading to Landau hydrodynamics. Since in real-life heavy ion collisions the large Bjorken x part of nuclear wave functions continues to move along the light cone trajectories of the incoming nuclei leaving the small-x partons behind, we conclude that a pure large coupling approach is not likely to adequately model nuclear collisions. We show that to account for small-coupling effects one can model the colliding nuclei by two (unphysical) ultrarelativistic shock waves with zero net energy each (but with non-zero energy density). We use this model to study the energy density of the strongly-coupled matter created immediately after the collision. We argue that expansion of the energy density in the powers of proper time τ squared corresponds on the gravity side to a perturbative expansion of the metric in graviton exchanges. Using such expansion we reproduce our earlier result [1] that the energy density of produced matter at mid-rapidity starts out as a constant (of time) in heavy ion collisions at large coupling.

High-pT pion and kaon production in relativistic nuclear collisions

Abstract: High-p_T pion and kaon production is studied in relativistic proton-proton, proton-nucleus, and nucleus-nucleus collisions in a wide energy range. Cross sections are calculated based on perturbative QCD, augmented by a phenomenological transverse momentum distribution of partons (``intrinsic k_T''). An energy dependent width of the transverse momentum distribution is extracted from pion and charged hadron production data in proton-proton/proton-antiproton collisions. Effects of multiscattering and shadowing in the strongly interacting medium are taken into account. Enhancement of the transverse momentum width is introduced and parameterized to explain the Cronin effect. In collisions between heavy nuclei, the model over-predicts central pion production cross sections (more significantly at higher energies), hinting at the presence of jet quenching. Predictions are made for proton-nucleus and nucleus-nucleus collisions at RHIC energies.