Parton

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

Introduction to High-Energy Heavy-Ion Collisions

Abstract: The author has succeeded in writing a well-balanced textbook of the new field of ultra-relativistic heavy-ion collisions (RHICs). The book is primarily suited to theoretically oriented graduate students and researchers (both theorists and experimental physicists). After introducing the necessary kinematical variables and describing the phenomenology of nucleon--nucleon collisions, the author proceeds to elucidate various concepts of high-energy particle physics which are relevant to the study of RHICs. Among these are the hard-scattering model, the Schwinger particle production mechanism, the classical string model and the dual parton model. He then focuses on the concept of the quark--gluon plasma (QGP) and gives an overview of the methods and results of lattice gauge theory. The final chapters of the book are devoted to the creation of a QGP via heavy-ion collisions and its possible signatures. In great detail the author discusses dilepton production, suppression, photon production, Hanbury--Brown--Twiss interferometry and strangeness enhancement. The book is very well written and I can recommend it to all graduate students and researchers interested in the field of RHICs. However, the book has one shortcoming: it focuses on heavy-ion physics in the energy region E > 200 GeV/nucleon and higher. The physics of the hadron gas, important for the later stages of RHICs at CERN and dominant for beam energies in the BEVALAC/SIS/AGS range, is neglected. To acquire an overview of the entire field of RHICs, the reader would profit from a supplementary reading of the more introductory textbook Introduction to Relativistic Heavy-Ion Collisions by L Csernai.

Factorization Theorem For Drell-Yan At Low q_T And Transverse-Momentum Distributions On-The-Light-Cone

Abstract: We derive a factorization theorem for Drell-Yan process at low q_T using effective field theory methods. In this theorem all the obtained quantities are gauge invariant and the special role of the soft function--and its subtraction thereof--is emphasized. We define transverse-momentum dependent parton distribution functions (TMDPDFs) which are free from light-cone singularities while all the Wilson lines are defined on-the-light-cone. We show explicitly to first order in \alpha_s that the partonic Feynman PDF can be obtained from the newly defined partonic TMDPDF by integrating over the transverse momentum of the parton inside the hadron. We obtain a resummed expression for the TMDPDF, and hence for the cross section, in impact parameter space. The universality of the newly defined matrix elements is established perturbatively to first order in \alpha_s. The factorization theorem is validated to first order in \alpha_s and also the gauge invariance between Feynman and light-cone gauges.

Uncertainties of predictions from parton distributions I : experimental errors.

Abstract: We determine the uncertainties on observables arising from the errors on the experimental data that are fitted in the global MRST2001 parton analysis. By diagonalizing the error matrix we produce sets of partons suitable for use within the framework of linear propagation of errors, which is the most convenient method for calculating the uncertainties. Despite the potential limitations of this approach we find that it can be made to work well in practice. This is confirmed by our alternative approach of using the more rigorous Lagrange multiplier method to determine the errors on physical quantities directly. As particular examples we determine the uncertainties on the predictions of the charged-current deep-inelastic structure functions, on the cross-sections for W production and for Higgs boson production via gluon-gluon fusion at the Tevatron and the LHC, on the ratio of W- to W+ production at the LHC and on the moments of the non-singlet quark distributions. We discuss the corresponding uncertainties on the parton distributions in the relevant x,Q2 domains. Finally, we briefly look at uncertainties related to the fit procedure, stressing their importance and using $\sigma_W$ , $\sigma_H$ and extractions of $\alpha_S(M_Z^2)$ as examples. As a by-product of this last point we present a slightly updated set of parton distributions, MRST2002.