122580301
Kaons in dense matter: results from KaoS
The production of kaons and antikaons in nucleus-nucleus collisions has been studied with the kaon spectrometer at SIS/GSI. The K-/K+ ratio was measured in C + C, Ni + Ni and Au + Au collisions at 1.5 A GeV and was found to be almost independent of the system size. In Ni + Ni collisions at 1.93 A GeV we measured the phase-space distributions of K- and K+ mesons. Within the framework of transport models, the measured K+ and K- yields can only be explained if in-medium modifications of the K meson masses are assumed. In Au + Au collisions at 1 A GeV, we observe non-vanishing elliptic flow near mid-rapidity and in-plane flow at target rapidity for K+ mesons. This effect can be explained by transport models when a repulsive in-medium K+N potential is taken into account. The ratio of the K+ meson excitation functions for Au + Au and C + C collisions increases with decreasing beam energies. This effect is expected for a soft nuclear equation of state.
25947222
Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy-Ion Collisions.
The production of pions and kaons has been measured in 197Au+197Au collisions at beam energies from 0.6 to 1.5A GeV with the kaon spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions, whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.
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.
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.
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.
119373633
Review of the results of the KaoS Collaboration
The production of K+ and of K− mesons in heavy-ion collisions at beam energies of 1 to 2 A GeV has systematically been investigated with the kaon spectrometer KaoS. The ratio of the K+ production excitation function for Au+Au and for C+C reactions increases with decreasing beam energy, which is expected for a soft nuclear equation-of-state. A comprehensive study of the K+ and of the K− emission as a function of the size of the collision system, of the collision centrality, of the kaon energy, and of the polar emission angle has been performed. The K−/K+ ratio is found to be nearly constant as a function of the collision centrality and can be explained by the dominance of strangeness exchange. On the other hand, the spectral slopes and the polar emission patterns are different for K− and for K+. Furthermore the azimuthal distribution of the particle emission has been investigated. K+ mesons and pions are emitted preferentially perpendicular to the reaction plane as well in Au+Au as in Ni+Ni collisions. In contrast for K− mesons in Ni+Ni reactions an in-plane flow was observed for the first time at these incident energies.
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.
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.
119300543
Complete electroweak corrections to Higgs production in a Standard Model with four generations at the LHC
Abstract Complete electroweak two-loop corrections to the process gg → H are presented and discussed in a Standard Model with a fourth generation of heavy fermions. The latter is studied at the LHC to put exclusion limits on a fourth generation of heavy fermions. Therefore also a precise knowledge of the electroweak (EW) next-to-leading-order (NLO) corrections is important. The corrections due to the fourth generation are positive and large for a light Higgs boson, positive but relatively small around the t ¯ – t threshold and start to become negative for a Higgs boson mass around M H = 450 GeV . Increasing further the value of the Higgs boson mass, the EW NLO effects tend to become huge and negative, O ( − 100 % ) , around the heavy-fermion threshold, assumed at 1.2 TeV , so that gg-fusion becomes non-perturbative. Above that threshold they start to grow again and become positive around M H = 1.75 TeV . The behavior at even larger values of M H shows a positive enhancement, O ( + 100 % ) at M H = 3 TeV .
7670518
Moments of heavy quark current correlators at four-loop order in perturbative QCD
We present the result for the first moment of the scalar and axial-vector current correlator in third order of the strong coupling constant αs and give the details of a recent evaluation of the pseudo-scalar correlator. The results can be used to reduce the theoretical uncertainty due to higher order corrections for the determination of fundamental parameters of QCD in the context of lattice calculations.
120745369
Precise quark masses from R(s)
We discuss the extraction of the charm- and bottom-quark mass from the experimentally measured R -ratio in combination with higher order QCD corrections to moments of the vacuum polarization function. The results for the MS ¯ -masses are m c ( 3 GeV ) = 0.986 ( 13 ) GeV and m b ( 10 GeV ) = 3.609 ( 25 ) GeV .