We present the first official release of the nCTEQ nuclear parton distribution functions with errors. The main addition to the previous nCTEQ PDFs is the introduction of PDF uncertainties based on the Hessian method. Another important addition is the inclusion of pion production data from RHIC that give us a handle on constraining the gluon PDF. This contribution summarizes our results from arXiv:1509.00792 and concentrates on the comparison with other groups providing nuclear parton distributions.
We present the new nCTEQ15 set of nuclear parton distribution functions with uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear dependence using data on nuclei all the way up to 208^Pb. The uncertainties are determined using
the Hessian method with an optimal rescaling of the eigenvectors to accurately represent the uncertainties for the chosen tolerance criteria. In addition to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY) processes, we also include inclusive pion production data from RHIC to help constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of the data sets with specific nPDF flavor components, and asses the impact of individual experiments. We also provide comparisons of the nCTEQ15 set with recent fits from other groups.
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 availa
ble 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 $pm 5%$.
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 uni
versality 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.