Search results for "Chromodynamics"
showing 10 items of 1030 documents
Effective models of two-flavor QCD: from small towards large $m_q$
2009
We study effective models of chiral fields and Polyakov loop expected to describe the dynamics responsible for the phase structure of two-flavor QCD. We consider the chiral sector described either using a linear sigma model or a Nambu-Jona-Lasinio model and study how these models, on the mean-field level when coupled with the Polyakov loop, behave as a function of increasing bare quark (or pion) mass. We find qualitatively similar behaviors for the cases of the linear sigma model and the Nambu-Jona-Lasinio model and, by comparing with existing lattice data, show that one cannot conclusively decide which of the two approximate symmetries drives the phase transitions at the physical point.
Bottom quark mass from QCD sum rules for the υ system
1999
Abstract The talk presents an update of the bottom quark mass determination from QCD moment sum rules for the ϒ system by the authors [1]. Employing the MS scheme, we fund mb(mb) = 4.19 ± 0.06 GeV. The differences to our previous analysis will be discussed and we comment on the determination of th pole mass for the bottom quark.
Strange quark mass from Finite Energy QCD sum rules to five loops
2007
The strange quark mass is determined from a new QCD Finite Energy Sum Rule (FESR) optimized to reduce considerably the systematic uncertainties arising from the hadronic resonance sector. As a result, the main uncertainty in this determination is due to the value of $\Lambda_{QCD}$. The correlator of axial-vector divergences is used in perturbative QCD to five-loop order, including quark and gluon condensate contributions, in the framework of both Fixed Order (FOPT), and Contour Improved Perturbation Theory (CIPT). The latter exhibits very good convergence, leading to a remarkably stable result in the very wide range $s_0 = 1.0 - 4.0 {GeV}^2$, where $s_0$ is the radius of the integration co…
Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at s=13TeV
2018
The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|<0.8) in proton–proton (pp) collisions at a centre-of-mass energy of s=13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at s=7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: dσcc¯/dy|y=0=974±138(stat.)±140(syst.)±214(BR)μb and dσbb…
Heavy-strange meson decay constants in the continuum limit of quenched QCD
2007
We improve a previous quenched result for heavy-light pseudoscalar meson decay constants with the light quark taken to be the strange quark. A finer lattice resolution (a ~ 0.05 fm) in the continuum limit extrapolation of the data computed in the static approximation is included. We also give further details concerning the techniques used in order to keep the statistical and systematic errors at large lattice sizes L/a under control. Our final result, obtained by combining these data with determinations of the decay constant for pseudoscalar mesons around the D_s, follows nicely the qualitative expectation of the 1/m-expansion with a (relative) 1/m-term of about -0.5 GeV/m_PS. At the physic…
LIGHT QUARK MASSES FROM QCD SUM RULES
2013
Recent QCD sum rule determinations of the light quark masses are reviewed. In the case of the strange quark mass, possible uncertainties are discussed in the framework of finite energy sum rules.
Heavy-quark production in two-photon collisions
1993
Abstract Heavy quarks are copiously produced in two-photon collisions at e + e − colliders. We present the inclusive production rates and the final state distributions of the quarks, including QCD radiative corrections for the leading subprocesses. The results are compared with recent measurements of charmed particle production at PETRA and PEP, and predictions are given for TRISTAN and LEP energies.
Asymptotic 3-loop heavy flavor corrections to the charged current structure functions FLW+−W−(x,Q2) and F2W+−W−(x,Q2)
2016
We derive the massive Wilson coefficients for the heavy flavor contributions to the nonsinglet charged current deep-inelastic scattering structure functions ${F}_{L}^{{W}^{+}}(x,{Q}^{2})\ensuremath{-}{F}_{L}^{{W}^{\ensuremath{-}}}(x,{Q}^{2})$ and ${F}_{2}^{{W}^{+}}(x,{Q}^{2})\ensuremath{-}{F}_{2}^{{W}^{\ensuremath{-}}}(x,{Q}^{2})$ in the asymptotic region ${Q}^{2}\ensuremath{\gg}{m}^{2}$ to 3-loop order in quantum chromodynamics at general values of the Mellin variable $N$ and the momentum fraction $x$. Besides the heavy quark pair production, also the single heavy flavor excitation $s\ensuremath{\rightarrow}c$ contributes. Numerical results are presented for the charm quark contributions, …
Towards leading isospin breaking effects in mesonic masses with $O(a)$ improved Wilson fermions
2017
We present an exploratory study of leading isospin breaking effects in mesonic masses using $O(a)$ improved Wilson fermions. Isospin symmetry is explicitly broken by distinct masses and electric charges of the up and down quarks. In order to be able to make use of existing isosymmetric QCD gauge ensembles we apply reweighting techniques. The path integral describing QCD+QED is expanded perturbatively in powers of the light quarks' mass deviations and the electromagnetic coupling. We employ QED$_{\mathrm{L}}$ as a finite volume formulation of QED.
Hadron structure at lowQ2
2007
This review deals with the structure of hadrons, strongly interacting many-body systems consisting of quarks and gluons. These systems have a size of about 1 fm, which shows up in scattering experiments at low momentum transfers $Q$ in the GeV region. At this scale the running coupling constant of Quantum Chromodynamics (QCD), the established theory of the strong interactions, becomes divergent. It is therefore highly intriguing to explore this theory in the realm of its strong interaction regime. However, the quarks and gluons can not be resolved at the GeV scale but have to be studied through their manifestations in the bound many-body systems, for instance pions, nucleons and their reson…