Theory of W and Z boson production

Success of precision studies in W and Z boson production at the Tevatron and LHC depends on the progress in reducing theoretical uncertainties to the level of 1-2%. I review recent developments in theoretical understanding of W and Z boson production and remaining issues to be solved to meet demands of the near-future experiments.Comment: Contribution to the proceedings of the 15th Topical Conference on Hadron Collider Physics (HCP 2004, June 14-18, 2004, East Lansing, MI); 14 pages, 8 figure

A meta-analysis of parton distribution functions

A "meta-analysis" is a method for comparison and combination of nonperturbative parton distribution functions (PDFs) in a nucleon obtained with heterogeneous procedures and assumptions. Each input parton distribution set is converted into a "meta-parametrization" based on a common functional form. By analyzing parameters of the meta-parametrizations from all input PDF ensembles, a combined PDF ensemble can be produced that has a smaller total number of PDF member sets than the original ensembles. The meta-parametrizations simplify the computation of the PDF uncertainty in theoretical predictions and provide an alternative to the 2010 PDF4LHC convention for combination of PDF uncertainties. As a practical example, we construct a META ensemble for computation of QCD observables at the Large Hadron Collider using the next-to-next-to-leading order PDF sets from CTEQ, MSTW, and NNPDF groups as the input. The META ensemble includes a central set that reproduces the average of LHC predictions based on the three input PDF ensembles and Hessian eigenvector sets for computing the combined PDF+$\alpha_s$ uncertainty at a common QCD coupling strength of 0.118.Comment: version to appear on JHE

Universality of transverse momentum resummation for electroweak boson production

We perform a global analysis of transverse momentum distributions in Drell-Yan pair and Z boson production in order to investigate universality of nonperturbative contributions to the Collins-Soper-Sterman resummed form factor. Our fit made in an improved nonperturbative model suggests that the nonperturbative contributions follow universal nearly-linear dependence on the logarithm of the heavy boson invariant mass Q, which closely agrees with an estimate from the infrared renormalon analysis.Comment: 5 pages, 1 figure; contribution to the proceedings of the XIII International Workshop on Deep Inelastic Scattering (DIS 2005, April 27 - May 1, 2005, Madison, WI, U.S.A.

Nonperturbative contributions to a resummed leptonic angular distribution in inclusive neutral vector boson production

We present an analysis of nonperturbative contributions to the transverse momentum distribution of $Z/\gamma^*$ bosons produced at hadron colliders. The new data on the angular distribution $\phi^*_\eta$ of Drell-Yan pairs measured at the Tevatron is shown to be in excellent agreement with a perturbative QCD prediction based on the Collins-Soper-Sterman (CSS) resummation formalism at NNLL accuracy. Using these data, we determine the nonperturbative component of the CSS resummed cross section and estimate its dependence on arbitrary resummation scales and other factors. With the scale dependence included at the NNLL level, a significant nonperturbative component is needed to describe the angular data.Comment: 36 pages, 10 figures, regular article. Revised version accepted for a publication in Phys.Rev.

Massive neutral gauge boson production as a probe of nuclear modifications of parton distributions at the LHC

We analyze the role of nuclear modifications of parton distributions, notably, the nuclear shadowing and antishadowing corrections, in production of lepton pairs from decays of neutral electroweak gauge bosons in proton-lead and lead-collisions at the LHC. Using the Collins-Soper-Sterman resummation formalism that we extended to the case of nuclear parton distributions, we observed a direct correlation between the predicted behavior of the transverse momentum and rapidity distributions of the produced vector bosons and the pattern of quark and gluon nuclear modifications. This makes Drell-Yan pair production in $pA$ and $AA$ collisions at the LHC a useful tool for constraining nuclear PDFs in the small-$x$ shadowing and moderate-$x$ antishadowing regions.Comment: 33 pages, 17 figure