Search results for "quantum chromodynamics"
showing 10 items of 1027 documents
K--pipi amplitudes from lattice QCD with a light charm quark.
2006
4 pages, 1 figure.-- PACS nrs.: 12.38.Gc, 13.25.Es, 11.30.Rd.-- ISI Article Identifier: 000244420700019.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0607220
Gluon contribution to hadronicJψproduction
1978
Using the recent CERN and Fermilab measurements for J/ψ production by π±, K±, p and p beams we show, within the framework of QCD, that only a combined version of light quark qq→cc fusion and gluon gg→cc fusion mechanisms can account for the various total cross section beam ratios as well as for the observed xF‐distributions.
Unified QCD determination of all pseudoscalar leptonic decay constants
1992
Leptonic decay constants of all pseudoscalar mesons are determined in QCD by means of a new QCD sum-rule method. In the light meson and heavy quark limit the results are very similar and also agree with the well-known PCAC and scaling predictions respectively. The corrections to light meson pole dominance are generally small while those to the heavy quark limit are found to be sensitive to the binding energy (i.e. meson and quark mass differences). For standard values of quark masses we obtainfπ=132 MeV,fk=161 MeV,fB=128±28 MeV,fD=175±13 MeV,fBs=144±30 MeV andfDs=193±12 MeV.
Quark gap equation within the analytic approach to QCD
2005
The compatibility between the QCD analytic invariant charge and chiral symmetry breaking is examined in detail. The coupling in question incorporates asymptotic freedom and infrared enhancement into a single expression, and contains only one adjustable parameter with dimension of mass. When inserted into the standard form of the quark gap-equation it gives rise to solutions displaying singular confining behavior at the origin. By relating these solutions to the pion decay constant, a rough estimate of about 880 MeV is obtained for the aforementioned mass-scale.
Measurement of jet charge in dijet events froms=8 TeVppcollisions with the ATLAS detector
2016
The momentum-weighted sum of the charges of tracks associated to a jet is sensitive to the charge of the initiating quark or gluon. This paper presents a measurement of the distribution of momentum ...
O(αs) longitudinal spin polarization in heavy-quark production
1995
We present the massive one-loop QCD corrections to the production cross sections of polarized quarks in the annihilation process ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}qq\ifmmode\bar\else\textasciimacron\fi{}(g) for bottom, top, and charm quarks. From the full analytical expressions for the production cross sections, Schwinger-type interpolation formulas for all parity-parity combinations (VV, VA, AA) are derived. The parity-odd interpolation formula contains the correct limit for vanishing quark masses taking into account a residual coupling of left- and right-chiral states in the massless theory. Numerical results for the total cross section and …
Color decomposition of multi-quark one-loop QCD amplitudes
2014
In this talk we discuss the color decomposition of tree-level and one-loop QCD amplitudes with arbitrary numbers of quarks and gluons. We present a method for the decomposition of partial amplitudes into primitive amplitudes, which is based on shuffle relations and is purely combinatorial. Closed formulae are derived, which do not require the inversion of a system of linear equations.
Scalar diagrammatic rules for Born amplitudes in QCD
2005
We show that all Born amplitudes in QCD can be calculated from scalar propagators and a set of three- and four-valent vertices. In particular, our approach includes amplitudes with any number of quark pairs. The quarks may be massless or massive. The proof of the formalism is given entirely within quantum field theory.
On the Structure of Infrared Singularities of Gauge-Theory Amplitudes
2009
A closed formula is obtained for the infrared singularities of dimensionally regularized, massless gauge-theory scattering amplitudes with an arbitrary number of legs and loops. It follows from an all-order conjecture for the anomalous-dimension matrix of n-jet operators in soft-collinear effective theory. We show that the form of this anomalous dimension is severely constrained by soft-collinear factorization, non-abelian exponentiation, and the behavior of amplitudes in collinear limits. Using a diagrammatic analysis, we demonstrate that these constraints imply that to three-loop order the anomalous dimension involves only two-parton correlations, with the possible exception of a single c…
Laurent series expansion of a class of massive scalar one-loop integrals toO(ε2)
2005
We use dimensional regularization to calculate the O({epsilon}{sup 2}) expansion of all scalar one-loop one-, two-, three-, and four-point integrals that are needed in the calculation of hadronic heavy quark production. The Laurent series up to O({epsilon}{sup 2}) is needed as input to that part of the next-to-next-to-leading order corrections to heavy flavor production at hadron colliders where the one-loop integrals appear in the loop-by-loop contributions. The four-point integrals are the most complicated. The O({epsilon}{sup 2}) expansion of the three- and four-point integrals contains in general polylogarithms up to Li{sub 4} and functions related to multiple polylogarithms of maximal …