Search results for "Chromodynamics"
showing 10 items of 1030 documents
QCD JETS AT HERA I.: O(αs) RADIATIVE CORRECTIONS TO ELECTROWEAK CROSS SECTIONS AND JET RATES
1989
We present the complete O(αs) corrections to the electroweak cross sections of both neutral current and charged current deep inelastic e±p scattering including lepton polarization effects. Changes in the cross section due to the inclusion of next-to-leading-log (NLL) effects are parametrized by K factors, which are defined as the ratio of the NLL O(αs) cross sections and the Born cross section. Using the standard redefinition scheme of the parton densities, we find that the K factors deviate substantially from unity for small values of the Bjorken-Scaling variable x. We also elaborate on problems that arise when defining jet cross sections in ep scattering and present numerical results for…
Constituent-quark model description of triply heavy-baryon nonperturbative lattice QCD data
2015
This paper provides results for the spectra of triply charmed and bottom baryons based on a constituent quark model approach. We take advantage of the assumption that potential models are expected to describe triply heavy baryons to a similar degree of accuracy as the successful results obtained in the charmonium and bottomonium sectors. The high precision calculation of the ground state and positive and negative parity excited states recently reported by nonperturbative lattice QCD provides us with a unique opportunity to confront model predictions with data. This comparison may also help to build a bridge between two difficult to reconcile lattice QCD results, namely, the lattice SU(3) QC…
On the Delta-nucleon and rho-pi splittings: A QCD-inspired look in free hadrons versus nuclei
1997
Relationships between mass intervals for free hadrons and in nuclei are studied in two theoretical approaches inspired by QCD: naive quark model and skyrmion model, taking one example each from mesons and baryons, that of pi-rho splitting in mesons, and nucleon-Delta splitting in baryons. Possible deconfinement effects in nuclei are examined.
A Quark model analysis of the Sivers function.
2008
We develop a formalism to evaluate the Sivers function. The approach is well suited for calculations which use constituent quark models to describe the structure of the nucleon. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model of hadron structure. The results obtained are consistent with a sizable Sivers effect and the signs for the u and d flavor contributions turn out to be opposite. This pattern is in agreement with the one found analyzing, in the same model, the impact parameter dependent generalized parton distributions. The Burkardt Sum Rule turns out to be fulfilled to a large extent. We estimate the QCD evolution of our results from the mom…
Charged-pion cross sections and double-helicity asymmetries in polarizedp+pcollisions ats=200 GeV
2015
We present midrapidity charged-pion invariant cross sections, the ratio of the pi(-) to pi(+) cross sections and the charge-separated double-spin asymmetries in polarized p + p collisions at root s = p + 200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The char…
Nonfactorizable corrections toB→J/ψK
2003
We apply the method of QCD light-cone sum rules to calculate nonfactorizable contributions to the $\stackrel{\ensuremath{\rightarrow}}{B}J/\ensuremath{\psi}K$ decay and estimate soft nonfactorizable corrections to the ${a}_{2}$ parameter. The corrections appear to be positive, favoring the positive sign of ${a}_{2},$ in agreement with recent theoretical considerations and experimental data. Our result also confirms expectations that in the color-suppressed decay nonfactorizable corrections are sizable.
Direct photon production in Pb–Pb collisions atsNN=2.76 TeV
2016
Direct photon production at mid-rapidity in Pb–Pb collisions at √sNN = 2.76 TeV was studied in the transverse momentum range 0.9<pT<14 GeV/c. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the ALICE detector material with the e+e− pair reconstructed in the central tracking system. The results of the two methods were combined and direct photon spectra were measured for the 0–20%, 20–40%, and 40–80% centrality classes. For all three classes, agreement was found with perturbative QCD calculations for pT≳5 GeV/c. Direct photon spectra down to pT≈1 GeV/c could be extracted for the 20–40% and 0–20% centrality classes. The significance of th…
The Institute for Nuclear Physics at the University of Mainz
2008
MAMI, the MAinz MIcrotron, has become a synonym for a cw electron scattering facility in the 1.5 14;GeV range with an outstanding beam quality and reliability. The Institute for Nuclear Physics (IKP) at the Johannes Gutenberg-University of Mainz, the home of MAMI, has developed and built this cascade of four recirculating machines for precision scattering experiments mostly with polarized electrons and photons for research in the field of hadron and nuclear physics. The central physics topic is the investigation of strongly interacting systems with the electroweak probe. This field, nowadays called strong QCD, which means QCD in the strongly coupled, non perturbative regime, still poses a n…
Wγproduction in vector boson fusion at NLO in QCD
2014
The next-to-leading order QCD corrections to ${W}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\gamma}$ production in association with two jets via vector boson fusion are calculated, including the leptonic decay of the $W$ with full off-shell effects and spin correlations. The process lends itself to a test of quartic gauge couplings. The next-to-leading order corrections reduce the scale uncertainty significantly and show a nontrivial phase space dependence.
Measurement of the production cross section of an isolated photon associated with jets in proton-proton collisions ats=7 TeVwith the ATLAS detector
2012
A measurement of the cross section for the production of an isolated photon in association with jets in proton-proton collisions at a center-of-mass energy root s = 7 TeV is presented. Photons are ...