Parton

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

Higgs-boson production through gluon fusion at NNLO QCD with parton showers

Abstract: We discuss how the UN2LOPS scheme for matching next-to-next-to-leading order (NNLO) calculations to parton showers can be applied to processes with large higher-order perturbative QCD corrections. We focus on Higgs-boson production through gluon fusion as an example. We also present an NNLO fixed-order event generator for this reaction.

Finding jets and summing soft gluons: A New algorithm

Abstract: We examine a new algorithm for finding jets ine+e− annihilation, using a jet measure based on relative transverse momentum. We perform an analytic calculation of the three-jet fraction at lowest order, and compare our result with the standard jet-finding algorithm. For soft gluons in an abelian theory it is shown that the leading double logarithms exponentiate, unlike the situation for the commonly used algorithm based on invariant mass. In QCD we find that there are leading non-abelian logarithms, and we calculate these explicitly atO(αs2). We discuss the modifications to the algorithm which are needed when the mass of a parton cluster is taken into account. The hope is that the new algorithm will allow an improved theoretical analysis at smaller values of the resolution parameteryT, and hence an improved fit to the experimental data.

Influence of Bottom Quark Jet Quenching on Single Electron Tomography of Au+Au

Abstract: Influence of Bottom Quark Jet Quenching on Single Electron Tomography of Au+Au Magdalena Djordjevic, 1 Miklos Gyulassy, 1 Ramona Vogt, 2 and Simon Wicks 1 Department of Physics, Columbia University, 538 West 120-th Street, New York, NY 10027 Nuclear Science Division, LBNL, Berkeley, CA 94720 and Physics Department, University of California, Davis, California 95616 (Dated: July 21, 2005) High transverse momentum single (non-photonic) electrons are shown to be sensitive to the stop- ping power of both bottom, b, and charm, c, quarks in AA collisions. We apply the DGLV theory of radiative energy loss to predict c and b quark jet quenching and compare the FONLL and PYTHIA heavy flavor fragmentation and decay schemes. We show that single electrons in the p T = 5 − 10 GeV range are dominated by the decay of b quarks rather than the more strongly quenched c quarks in Au+Au collisions at s = 200 AGeV. The smaller b quark energy loss, even for extreme opacities with gluon rapidity densities up to 3500, is predicted to limit the nuclear modification factor, R AA , of single electrons to the range R AA ∼ 0.5−0.6, in contrast to previous predictions of R AA 3 GeV in pp collisions. In this letter, we show that jet quenching further amplifies the b contribution to the lepton spectrum and strongly limits the nuclear modification factor of electrons in AA collisions. The preliminary electron data [24]-[25] are so surpris- ing that novel jet energy loss mechanisms may have to be postulated [28]-[31]. The elliptic flow of high p T heavy quarks can be accounted for, e.g., if the elastic cross sec- tions of all partons, including bottom, are assumed to be anomalously enhanced to > 20 mb, far in excess of per- turbative QCD predictions, up to at least p T ∼ 10 GeV. While these enhanced cross sections could lead to heavy flavor elliptic flow at the pion level even at high p T , they may greatly overestimate the attenuation of light and heavy flavored hadrons [31]-[33]. Given the critical role that single electron tomography of the sQGP may play in the near future, it is especially important to scrutinize the theoretical uncertainties and robustness of current predictions. This is the aim of this letter. Theoretical framework. The calculation of the lepton spectrum includes initial

Hadron production in p+p, p+Pb, and Pb+Pb collisions with the hijing 2.0 model at energies available at the CERN Large Hadron Collider

Abstract: The Heavy-Ion Jet Interaction Generator (hijing) Monte Carlo model is updated with the latest parton distributions functions and a new set of the parameters in the two-component minijet model that controls the total p+p cross section and the central pseudorapity density. We study hadron spectra and multiplicity distributions using the hijing2.0 model and compare to recent experimental data from p+p collisions at the Large Hadron Collider (LHC) energies. We also give predictions of hadron production in p+p, p+Pb, and Pb+Pb collisions at the full LHC energy.

A Field Theoretic Model for electron-Nucleon Deep Inelastic Scattering

Abstract: The structure functions for inelastic electron-nucleon scattering are studied in the Bjorken limit in the framework of canonical field theory. The "parton" model of Feynman is derived and the structure functions' asymptotic behavior for large energy transfers is computed.