56053259
Leptonic contributions to the effective electromagnetic coupling at four-loop order in QED
Abstract The running of the effective electromagnetic coupling is for many electroweak observables the dominant correction. It plays an important role for deriving constraints on the Standard Model in the context of electroweak precision measurements. We compute the four-loop QED corrections to the running of the effective electromagnetic coupling and perform a numerical evaluation of the different gauge invariant subsets.
15203131
Precise charm- and bottom-quark masses: Theoretical and experimental uncertainties
We consider recent theoretical and experimental improvements in determining charm- and bottom-quark masses. We present a new, improved evaluation of the contribution of the gluon condensate 〈αsG2/π〉 to the charm mass determination and a detailed study of potential uncertainties in the continuum cross section for $b\bar b$ production, together with a study of the parametric uncertainty from the αs-dependence of our results. The final results, mc(3 GeV) = 986(13) MeV and mb(mb) = 4163(16) MeV, together with the closely related lattice determination mc(3 GeV) = 986(6) MeV, currently represent the most precise determinations of these two fundamental standard-model parameters. We critically analyze the theoretical and experimental uncertainties.
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.
427206
Four-loop moments of the heavy quark vacuum polarization function in perturbative QCD
New results at four-loop order in perturbative QCD for the first two Taylor coefficients of the heavy quark vacuum polarization function are presented. They can be used to perform a precise determination of the charm- and bottom-quark mass. Implications for the value of the quark masses are briefly discussed.
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.
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.
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.
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.
10220872
Is a soft nuclear equation of state extracted from heavy-ion data incompatible with pulsar data?
We discuss the recent constraints on the nuclear equation of state (EoS) from pulsar mass measurements and from subthreshold production of kaons in heavy-ion collisions. While the recent pulsar data point towards a hard EoS, the analysis of the heavy-ion data allows only for soft equations of state. We resolve the apparent contradiction by considering the different density regimes probed. We argue that future measurements of global properties of low-mass pulsars can serve as an excellent cross-check to the heavy-ion data.
17217990
First measurement of antikaon phase-space distributions in nucleus–nucleus collisions at subthreshold beam energies
Abstract Differential production cross sections of K − and K + mesons have been measured as function of the polar emission angle in Ni + Ni collisions at a beam energy of 1.93  A GeV. In near-central collisions, the spectral shapes and the widths of the rapidity distributions of K − and K + mesons are in agreement with the assumption of isotropic emission. In non-central collisions, the K − and K + rapidity distributions are broader than expected for a single thermal source. In this case, the polar angle distributions are strongly forward–backward peaked and the nonisotropic contribution to the total yield is about one third both for K + and K − mesons. The K − /K + ratio is found to be about 0.03 independent of the centrality of the reaction. This value is significantly larger than predicted by microscopic transport calculations if in-medium modifications of K mesons are neglected.
119152945
Soft nuclear equation-of-state from heavy-ion data and implications for compact stars
Measurements of kaon production at subthreshold energies in heavy-ion collisions point to a soft nuclear equation-of-state for densities up to 2-3 times nuclear matter saturation density. We apply these results to study the implications on compact star properties, especially in the context of the recent measurement of the two solar mass pulsar PSR J1614-2230. The implications are two-fold: Firstly, the heavy-ion results constrain nuclear matter at densities relevant to light neutron stars. Hence, a radius measurement could provide information about the density dependence of the symmetry energy which is a crucial quantity in nuclear physics. Secondly, the information on the nucleon potential obtained from the analysis of the heavy-ion data can be combined with restrictions from causality on the nuclear equation-of-state. From this we can derive a limit for the highest allowed compact star mass of three solar masses.