A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work signiflcantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errorsforbothnewandolddata sets; (ii) asystematic 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 flts. A numberofphysicsissues,particularlyrelatingtothebehaviorofthegluondistribution,are addressedinmorequantitativetermsthanbefore. Extensiveresultsontheuncertaintiesof 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, basedoncurrentknowledgeofthepartondistributions. Inparticular, theuncertaintieson the production cross sections of the W, Z at the Tevatron and the LHC are estimated to be§4% and§5%, respectively, and that of a light Higgs at the LHC to be§5%.

/pdf/new-generation-of-parton-distributions-with-uncertainties-4f8pm2a8i5.pdf

New generation of parton distributions with uncertainties from global QCD analysis

We present updated leading-order, next-to-leading order and next-to-next-to-leading order parton distribution functions (“MSTW 2008”) determined from global analysis of hard-scattering data within the standard framework of leading-twist fixed-order collinear factorisation in the $\overline{\mathrm{MS}}$
 
scheme. These parton distributions supersede the previously available “MRST” sets and should be used for the first LHC data taking and for the associated theoretical calculations. New data sets fitted include CCFR/NuTeV dimuon cross sections, which constrain the strange-quark and -antiquark distributions, and Tevatron Run II data on inclusive jet production, the lepton charge asymmetry from W decays and the Z rapidity distribution. Uncertainties are propagated from the experimental errors on the fitted data points using a new dynamic procedure for each eigenvector of the covariance matrix. We discuss the major changes compared to previous MRST fits, briefly compare to parton distributions obtained by other fitting groups, and give predictions for the W and Z total cross sections at the Tevatron and LHC.

/pdf/parton-distributions-for-the-lhc-4lvvi85r8i.pdf

Parton distributions for the LHC

We present NNPDF3.0, the first set of parton distribution functions (PDFs) determined with a methodology validated by a closure test. NNPDF3.0 uses a global dataset including HERA-II deep-inelastic inclusive cross-sections, the combined HERA charm data, jet production from ATLAS and CMS, vector boson rapidity and transverse momentum distributions from ATLAS, CMS and LHCb, W+c data from CMS and top quark pair production total cross sections from ATLAS and CMS. Results are based on LO, NLO and NNLO QCD theory and also include electroweak corrections. To validate our methodology, we show that PDFs determined from pseudo-data generated from a known underlying law correctly reproduce the statistical distributions expected on the basis of the assumed experimental uncertainties. This closure test ensures that our methodological uncertainties are negligible in comparison to the generic theoretical and experimental uncertainties of PDF determination. This enables us to determine with confidence PDFs at different perturbative orders and using a variety of experimental datasets ranging from HERA-only up to a global set including the latest LHC results, all using precisely the same validated methodology. We explore some of the phenomenological implications of our results for the upcoming 13 TeV Run of the LHC, in particular for Higgs production cross-sections.

/pdf/parton-distributions-for-the-lhc-run-ii-3k5n4fqkie.pdf

Parton distributions for the LHC Run II

Parton distributions with LHC data

Parton distribution functions (PDFs) are crucial ingredients for the calculation of the relevant cross sections for various scattering processes at the Large Hadron Collider (LHC). Including data from several previous experiments, the authors find new PDFs, which will be important for the data analysis at the LHC Run-2.

New parton distribution functions from a global analysis of quantum chromodynamics

Measurements of the ratio of Drell-Yan yields from an $800 \mathrm{GeV}/c$ proton beam incident on liquid hydrogen and deuterium targets are reported. Approximately 360 000 Drell-Yan muon pairs remained after all cuts on the data. From these data, the ratio of down antiquark $(\overline{d})$ to up $(\ifmmode \bar{u}\else \={u}\fi{})$ antiquark distributions in the proton sea is determined over a wide range in Bjorken-$x.$ These results confirm previous measurements by E866 and extend them to lower x. From these data, $(\overline{d}\ensuremath{-}\ifmmode \bar{u}\else \={u}\fi{})$ and $\ensuremath{\int}(\overline{d}\ensuremath{-}\ifmmode \bar{u}\else \={u}\fi{})dx$ are evaluated for $0.015lxl0.35.$ These results are compared with parametrizations of various parton distribution functions, models and experimental results from NA51, NMC and HERMES.

Improved measurement of the d̄/ū asymmetry in the nucleon sea

¯ 2u ) and *(d ¯ 2u ¯ )dx are evaluated for 0.015,x,0.35. These results are compared with parametrizations of various parton distribution functions, models and experimental results from NA51, NMC and HERMES.

/pdf/improved-measurement-of-the-d-u-asymmetry-in-the-nucleon-sea-3auglhnq98.pdf

Improved measurement of the d ¯ 'u asymmetry in the nucleon sea

Measurement of J/Psi and Psi' Suppression in p-A Collisions at 800 GeV/c

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Improved measurement of the d̄/ū asymmetry in the nucleon sea

Improved measurement of the d ¯ 'u asymmetry in the nucleon sea

Measurement of J/Psi and Psi' Suppression in p-A Collisions at 800 GeV/c