12101220
QCD corrections to single top quark production in electron-photon interactions
Abstract.Single top quark production in electron-photon interactions provides a clean environment for the measurement of the Cabibbo-Kobayashi-Maskawa matrix element Vtb. Aiming at an experimental precision at the percent level the knowledge of radiative corrections is important. In this paper we present results for the radiative corrections in quantum chromodynamics.
7975024
Recent Results on Four-loop Tadpoles
The experimental measurable R -ratio can be used to perform a precise determination of the charm- and bottom-quark mass with the help of theoretical computable expansion coefficients of the vacuum polarization function. The four-loop contributions in perturbative QCD to the first two expansion coefficients of the vacuum polarization functions are presented.
17743404
New Results in Four and Five Loop QED calculations
We report on two recent multiloop results in QED: (i) the four-loop corrections to the conversion relations between the QED charge renormalized in the on-shell and MS ¯ schemes; (ii) analytical evaluation of a class of asymptotic contributions to the muon anomaly at five-loops.
119202777
Two-Loop Virtual Corrections to Drell-Yan Production at order $\alpha_s \alpha^3$
The Drell-Yan mechanism for the production of lepton pairs is one of the most basic processes for physics studies at hadron colliders. It is therefore important to have accurate theoretical predictions. In this work we compute the two-loop virtual mixed QCD x QED corrections to Drell-Yan production. We evaluate the Feynman diagrams by decomposing the amplitudes into a set of known master integrals and their coefficients, which allows us to derive an analytical result. We also perform a detailed study of the ultraviolet and infrared structure of the two-loop amplitude and the corresponding poles in epsilon.
118683322
Charm and Bottom Quark Masses: An Update
Using new four-loop results for the heavy quark vacuum polarization and new data for bottom quark production in electron-positron annihilation, an update on the determination of charm- and bottom-quark masses through sum rules has been performed. The previous result for the charm-quark mass, ${m}_{c}(3\text{ }\text{ }\mathrm{GeV})=0.986(13)\text{ }\text{ }\mathrm{GeV}$, based on the lowest moment, is supported by the new results from higher moments which lead to consistent values with comparable errors. The new value for the bottom quark, ${m}_{b}(10\text{ }\text{ }\mathrm{GeV})=3.610(16)\text{ }\text{ }\mathrm{GeV}$, corresponding to ${m}_{b}({m}_{b})=4.163(16)\text{ }\text{ }\mathrm{GeV}$, makes use of both the new data and the new perturbative results and is consistent with the earlier determination.
13361740
Heavy Quark Masses from Sum Rules in Four-Loop Approximation
Abstract New data for the total cross section σ ( e + e − → hadrons ) in the charm and bottom threshold region are combined with an improved theoretical analysis, which includes recent four-loop calculations, to determine the short distance MS ¯ charm and bottom quark masses. A detailed discussion of the theoretical and experimental uncertainties is presented. The final result for the MS ¯ -masses, m c ( 3 GeV ) = 0.986 ( 13 ) GeV and m b ( 10 GeV ) = 3.609 ( 25 ) GeV , can be translated into m c ( m c ) = 1.286 ( 13 ) GeV and m b ( m b ) = 4.164 ( 25 ) GeV . This analysis is consistent with but significantly more precise than a similar previous study.
20377841
First evidence for different freeze-out conditions for kaons and antikaons observed in heavy-ion collisions.
Differential production cross sections of K- and K+ mesons have been measured in Ni+Ni and Au+Au collisions at a beam energy of 1.5 A GeV. The K(-)/K(+) ratio is found to be nearly constant as a function of the collision centrality and system size. The spectral slopes and the polar emission pattern differ for K- and K+ mesons. These observations indicate that K+ mesons decouple earlier from the fireball than K- mesons.
121748724
Kaon and antikaon production in dense nuclear matter
The production and propagation of kaons and antikaons in relativistic heavy-ion collisions have been systematically investigated with the Kaon spectrometer at SIS/GSI. Experimental results on the K+ and K− yield and on the azimuthal emission pattern of K+ mesons are presented. Within the framework of transport models the data can be explained assuming in-medium kaon–nucleon potentials. The comparison of K+ production excitation functions obtained for Au+Au and C+C collisions with results of transport model calculations favours a soft nuclear equation-of-state.
122693943
Kaon and pion emission in asymmetric C+Au and Au+C collisions at 1.0A GeV and 1.8A GeV
The emission of K{sup +} and {pi}{sup {+-}} mesons has been studied in the asymmetric collision system Au+C and in the inverse reaction C+Au at 1.0A GeV (and at 1.8A GeV for C+Au only) in order to extract the effective source rapidities based on their distribution in the p{sub t}-y plane. The extracted source rapidity of K{sup +} mesons is about y{sub s}/y{sub beam}=0.25 at both incident energies [y(Au)=0,y(C)=y{sub beam}]. This corresponds to a reaction volume consisting of the C nucleus and a tube cut out of the Au nucleus. In clear contrast, the source rapidities of {pi}{sup {+-}} mesons vary from y{sub s}/y{sub beam}=0.5 in peripheral collisions (corresponding to NN interactions) to about y{sub s}/y{sub beam}<0.33 in central reactions. The multiplicities of K{sup +} and {pi} are compared to symmetric collision systems and, together with detailed transport model calculations, are used to study the sensitivity to the nuclear equation of state.
54021017
Implications for compact stars of a soft nuclear equation of state from heavy-ion data
We study the implications on compact star properties of a soft nuclear equation of state determined from kaon production at subthreshold energies in heavy-ion collisions. On one hand, we apply these results to study radii and moments of inertia of light neutron stars. Heavy-ion data provides constraints on nuclear matter at densities relevant for those stars and, in particular, to the density dependence of the symmetry energy of nuclear matter. On the other hand, we derive a limit for the highest allowed neutron star mass of three solar masses. For that purpose, we use the information on the nucleon potential obtained from the analysis of the heavy-ion data combined with causality on the nuclear equation of state.
119236403
Neutron star versus heavy-ion data: is the nuclear equation of state hard or soft?
Recent astrophysical observations of neutron stars and heavy-ion data are confronted with our present understanding of the equation of state of dense hadronic matter. Emphasis is put on the possible role of the presence of hyperons in the interior of compact stars. We argue that data from low-mass pulsars provide an important cross-check between high-density astrophysics and heavy-ion physics.