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Register a new userCT10 parton distributions and other developments in the global QCD analysis
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We summarize several projects carried out by the CTEQ global analysis of parton distribution functions (PDFs) of the proton during 2010. We discuss a recently released CT10 family of PDFs with a fixed and variable QCD coupling strength; implementation of combined HERA and Tevatron lepton asymmetry data sets; theoretical issues associated with the analysis of $W$ charge asymmetry in PDF fits; PDFs for leading-order shower programs; and constraints on new color-octet fermions from the hadronic data.
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The CTEQ program for the determination of parton distributions through a global QCD analysis of data for various hard scattering processes is fully described. A new set of distributions, CTEQ3, incorporating several new types of data is reported and compared to the two previous sets of CTEQ distributions. Comparison with current data is discussed in some detail. The remaining uncertainties in the parton distributions and methods to further reduce them are assessed. Comparisons with the results of other global analyses are also presented.
We present the first Monte Carlo based global QCD analysis of spin-averaged and spin-dependent parton distribution functions (PDFs) that includes nucleon isovector matrix elements in coordinate space from lattice QCD. We investigate the degree of universality of the extracted PDFs when the lattice and experimental data are treated under the same conditions within the Bayesian likelihood analysis. For the unpolarized sector, we find rather weak constraints from the current lattice data on the phenomenological PDFs, and difficulties in describing the lattice matrix elements at large spatial distances. In contrast, for the polarized PDFs we find good agreement between experiment and lattice data, with the latter providing significant constraints on the spin-dependent isovector quark and antiquark distributions.
We perform the first global QCD analysis of pion valence, sea quark, and gluon distributions within a Bayesian Monte Carlo framework with threshold resummation on Drell-Yan cross sections at next-to-leading log accuracy. Exploring various treatments of resummation, we find that the large-$x$ asymptotics of the valence quark distribution $sim (1-x)^{beta_v}$ can differ significantly, with $beta_v$ ranging from $approx 1$ to $> 2.5$ at the input scale. Regardless of the specific implementation, however, the resummation induced redistribution of the momentum between valence quarks and gluons boosts the total momentum carried by gluons to $approx 40%$, increasing the gluon contribution to the pion mass to $approx 40$ MeV.
A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work includes a full treatment of available experimental correlated systematic errors for both new and old data sets and a systematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions. The new gluon distribution is considerably harder than that of previous standard fits. Extensive results on the uncertainties of parton distributions at various scales, and on parton luminosity functions at the Tevatron RunII and the LHC, are obtained. The latter provide the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, such as the production cross sections of the $W,Z$ at the Tevatron and the LHC, and that of a light Higgs.
A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work significantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errors for both new and old data sets; (ii) a systematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions, using a recently developed eigenvector-basis approach to the Hessian method. The new gluon distribution is considerably harder than that of previous standard fits. A number of physics issues, particularly relating to the behavior of the gluon distribution, are addressed in more quantitative terms than before. Extensive results on the uncertainties of parton distributions at various scales, and on parton luminosity functions at the Tevatron RunII and the LHC, are presented. The latter provide the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, based on current knowledge of the parton distributions. In particular, the uncertainties on the production cross sections of the $W,Z$ at the Tevatron and the LHC are estimated to be $pm 4%$ and $pm 5%$ respectively, and that of a light Higgs at the LHC to be $pm 5%$.
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