456 research outputs found

    Struktura hadrona iz inkluzivnih i ekskluzivnih udarnih presjeka u ep raspršenju

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    The contribution of both inclusive and exclusive cross-section data from HERA to our knowledge of parton distribution functions is reviewed and future prospects are outlined.Dajemo pregled doprinosa poznavanju funkcija partonskih raspodjela na osnovi inkluzivnih i ekskluzivnih udarnih presjeka iz HERE te izla┼żemo budu─ça istra┼żivanja

    Summary of the Structure Functions Working group at DIS 2012

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    A summary of the recent experimental, phenomenological and theoretical results presented in the Structure Functions working group at DIS2012 workshop.Comment: 12 pages, 9 figures, to be published in the Proceedings of the XX International Workshop on Deep Inelastic Scattering, University of Bonn, 26-30th March 201

    Uncertainties on low-x parton densities and the corresponding high-energy neutrino cross sections

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    A brief review of how parton densities are determined within the conventional DGLAP formalism of NLO QCD will be given with particular reference to the low-x region. Predictions for high energy neutrino and antineutrino charged and neutral current cross-sections using several different modern PDF fits will be compared. PDF uncertainties from model assumptions and parametrization bias are considered in addition to the experimental uncertainties. Particular attention is paid to assumptions and biases which could signal the need for extension of the conventional formalism to include effects such as ln(1/x) resummation or non-linear effects of high gluon density. See the published paper [1]

    Predictions for high energy neutrino cross-sections from the ZEUS global PDF fits

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    We have updated predictions for high energy neutrino and antineutrino charged current cross-sections within the conventional DGLAP formalism of NLO QCD using a modern PDF fit to HERA data, which also accounts in a systematic way for PDF uncertainties deriving from both model uncertainties and from the experimental uncertainties of the input data sets. Furthermore the PDFs are determined using an improved treatment of heavy quark thresholds. A measurement of the neutrino cross-section much below these predictions would signal the need for extension of the conventional formalism as in BFKL resummation, or even gluon recombination effects as in the colour glass condensate model.Comment: 10 pages (RevTeX4), 6 figures; expanded discussion of additional theoretical uncertainties at low x; accepted for publication in JHE

    A determination of mc(mc) from HERA data using a matched heavy-flavor scheme

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    The charm quark mass is one of the fundamental parameters of the Standard Model Lagrangian. In this work we present a determination of the MSbar charm mass from a fit to the inclusive and charm HERA deep-inelastic structure function data. The analysis is performed within the xFitter framework, with structure functions computed in the FONLL general-mass scheme as implemented in APFEL. In the case of the FONLL-C scheme, we obtain mc(mc) = 1.335 +- 0.043(exp) +0.019 -0.000(param) +0.011 -0.008(mod) +0.033 -0.008(th) GeV. We also perform an analogous determination in the fixed-flavor-number scheme at next-to-leading order, finding mc(mc) = 1.318 +- 0.054(exp) +0.011 -0.010(param) +0.015 -0.019(mod) +0.045 -0.004(th) GeV, compatible with the FONLL-C value. Our results are consistent with previous determinations from DIS data as well as with the PDG world average.Comment: 37 pages, 12 figures, 3 table

    Impact of heavy-flavour production cross sections measured by the LHCb experiment on parton distribution functions at low x

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    The impact of recent measurements of heavy-flavour production in deep inelastic epep scattering and in pppp collisions on parton distribution functions is studied in a QCD analysis in the fixed-flavour number scheme at next-to-leading order. Differential cross sections of charm- and beauty-hadron production measured by LHCb are used together with inclusive and heavy-flavour production cross sections in deep inelastic scattering at HERA. The heavy-flavour data of the LHCb experiment impose additional constraints on the gluon and the sea-quark distributions at low partonic fractions xx of the proton momentum, down to xÔł╝5├Ś10Ôłĺ6x \sim 5 \times 10^{-6}. This kinematic range is currently not covered by other experimental data in perturbative QCD fits

    What did HERA teach us about the structure of the proton?

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    Starting in 2008 the H1 and ZEUS experiments have been combining their data in order to provide the most complete and accurate set of deep-inelastic data as the legacy of HERA. The present review presents these combinations, both published and preliminary, and explores how they have been used to give information on the structure of the proton. The HERAPDF parton distribution functions (PDFs) are presented and compared with other current PDFs and with data from the Tevatron and LHC colliders.Comment: 49 pages, 49 figures, to be published in J.Phys.

    A posteriori inclusion of parton density functions in NLO QCD final-state calculations at hadron colliders: The APPLGRID Project

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    A method to facilitate the consistent inclusion of cross-section measurements based on complex final-states from HERA, TEVATRON and the LHC in proton parton density function (PDF) fits has been developed. This can be used to increase the sensitivity of LHC data to deviations from Standard Model predictions. The method stores perturbative coefficients of NLO QCD calculations of final-state observables measured in hadron colliders in look-up tables. This allows the posteriori inclusion of parton density functions (PDFs), and of the strong coupling, as well as the a posteriori variation of the renormalisation and factorisation scales in cross-section calculations. The main novelties in comparison to original work on the subject are the use of higher-order interpolation, which substantially improves the trade-off between accuracy and memory use, and a CPU and computer memory optimised way to construct and store the look-up table using modern software tools. It is demonstrated that a sufficient accuracy on the cross-section calculation can be achieved with reasonably small look-up table size by using the examples of jet production and electro-weak boson (Z, W) production in proton-proton collisions at a center-of-mass energy of 14 TeV at the LHC. The use of this technique in PDF fitting is demonstrated in a PDF-fit to HERA data and simulated LHC jet cross-sections as well as in a study of the jet cross-section uncertainties at various centre-of-mass energies

    Parton Distribution Functions of the Charged Pion Within The xFitter Framework

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    We present the first open-source analysis of parton distribution functions (PDFs) of charged pions using xFitter, an open-source QCD fit framework to facilitate PDF extraction and analyses. Our calculations are implemented at next-to-leading order (NLO) using APPLgrids generated by MCFM generator. Using currently available Drell-Yan and photon production data, we find the valence distribution is well constrained; however, the considered data are not sensitive enough to unambiguously determine sea and gluon distributions. Fractions of momentum carried by the valence, sea and gluon components are discussed, and we compare with the results of JAM collaboration and the GRV group.Comment: 9 pages, 6 figure
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