Search results for "QUANTUM CHROMODYNAMICS"
showing 10 items of 1027 documents
First global next-to-leading order determination of diffractive parton distribution functions and their uncertainties within the {\tt xFitter} framew…
2018
We present {\tt GKG18-DPDFs}, a next-to-leading order (NLO) QCD analysis of diffractive parton distribution functions (diffractive PDFs) and their uncertainties. This is the first global set of diffractive PDFs determined within the {\tt xFitter} framework. This analysis is motivated by all available and most up-to-date data on inclusive diffractive deep inelastic scattering (diffractive DIS). Heavy quark contributions are considered within the framework of the Thorne-Roberts (TR) general mass variable flavor number scheme (GM-VFNS). We form a mutually consistent set of diffractive PDFs due to the inclusion of high-precision data from H1/ZEUS combined inclusive diffractive cross sections me…
Multiplicity distributions and long range rapidity correlations
2010
The physics of the initial conditions of heavy ion collisions is dominated by the nonlinear gluonic interactions of QCD. These lead to the concepts of parton saturation and the Color Glass Condensate (CGC). We discuss recent progress in calculating multi-gluon correlations in this framework, prompted by the observation that these correlations are in fact easier to compute in a dense system (nucleus-nucleus) than a dilute one (proton-proton).
The pion polarisability from QCD sum rules
1994
Abstract The electromagnetic polarisability of charged pions, α E , has recently attracted both theoretical and experimental attention. Unfortunately the experimental results disagree with each other. We have investigated this polarisation via a QCD sum rule approach and find α E = 5.6 ± 0.5 × 10 −4 fm 3 , which is in agreement with one experiment and disagrees with the result of chiral perturbation theory.
Measurement of the differential cross-sections of inclusive, prompt and non-prompt J/ψ production in proton–proton collisions at s=7 TeV
2011
The inclusive J/psi production cross-section and fraction of J/psi mesons produced in B-hadron decays are measured in proton proton collisions at root s = 7 TeV with the ATLAS detector at the LHC, as a function of the transverse momentum and rapidity of the J/psi, using 2.3 pb(-1) of integrated luminosity. The cross-section is measured from a minimum P-T of 1 GeV to a maximum of 70 GeV and for rapidities within vertical bar y vertical bar < 2.4 giving the widest reach of any measurement of J/psi production to date. The differential production cross-sections of prompt and non-prompt J/psi are separately determined and are compared to Colour Singlet NNLO*, Colour Evaporation Model, and FONLL …
QCD Jets at HERA II.O(? s 2 ) four-jet cross-sections
1989
We present exact expressions for theO(α s 2 ) tree graph four-jet cross-sections in neutral current and charged current deep inelasticep scattering initiated by quarks, antiquarks and gluons including lepton polarization effects. Using helicity amplitudes the partonic cross-sections are given in concise form including all colour, flavour and statistical factors. We explicate the electroweak coupling dependence and state how the partonic cross-sections are folded with the respective parton densities to obtain theep jet cross-sections toO(α s 2 ). We present some numerical results for the neutral current one-photon exchange case. We elaborate on the cut dependence of the jet rates and present…
QCD corrections to static heavy-quark form factors
2005
Interactions of heavy quarks, in particular of top quarks, with electroweak gauge bosons are expected to be very sensitive to new physics effects related to electroweak symmetry breaking. These interactions are described by the so-called static form factors, which include anomalous magnetic moments and the effective weak charges. We compute the second-order QCD corrections to these static form factors, which turn out to be sizeable and need to be taken into account in searches for new anomalous coupling effects.
Double parton correlations in Light-Front constituent quark models
2014
Double parton distribution functions (dPDF) represent a tool to explore the 3D proton structure. They can be measured in high energy proton-proton and proton nucleus collisions and encode information on how partons inside a proton are correlated among each other. dPFDs are studied here in the valence quark region, by means of a constituent quark model, where two particle correlations are present without any additional prescription. This framework allows to understand the dynamical origin of the correlations and to clarify which, among the features of the results, are model independent. Use will be made of a relativistic light-front scheme, able to overcome some drawbacks of the previous cal…
A solution to the strong CP problem transforming the theta angle to the KM CP-violating phase
2010
It is shown that in the scheme with a rotating fermion mass matrix (i.e. one with a scale-dependent orientation in generation space) suggested earlier for explaining fermion mixing and mass hierarchy, the theta angle term in the QCD action of topological origin can be eliminated by chiral transformations, while giving still nonzero masses to all quarks. Instead, the effects of such transformations get transmitted by the rotation to the CKM matrix as the KM phase giving, for theta of order unity, a Jarlskog invariant typically of order 10(-5), as experimentally observed. Strong and weak CP violations appear then as just two facets of the same phenomenon.
Measurement of the top quark pair production cross-section with ATLAS in the single lepton channel
2012
A measurement of the production cross-section for top quark pairs (t[bar over t]) in pp collisions at √s = 7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in the single lepton topology by requiring an electron or muon, large missing transverse momentum and at least three jets. With a data sample of 35 pb[superscript −1], two different multivariate methods, one of which uses b-quark jet identification while the other does not, use kinematic variables to obtain cross-section measurements of σ[subscript t bar over t] = 187 ± 11 (stat.) [+18 over −17] (syst.) ± 6 (lumi.) pb and σ[subscript t bar over t] = 173 ± 17 (stat.) [+18 ove…
The hadronic contribution to the running of the electromagnetic coupling and the electroweak mixing angle
2019
37th International Symposium on Lattice Field Theory, Wuhan, China, 16 Jun 2019 - 22 Jun 2019; PoS(LATTICE 2019)010 (2019).