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.
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.
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.
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.
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.
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.
120793699
Quark masses from low-energy moments of heavy-quark current correlators
We present an update of the determination of charm- and bottom-quark masses from the lowenergy expansion of the vacuum polarization function in combination with experimental data for R(s). This analysis leads to the most precise determination of th e masses of the charm and bottom quarks: mc(3 GeV) = 986(13) MeV, mb(mb) = 4163(16) MeV.
16230066
Precise Charm and Bottom quark masses
Exploiting the analyticity of the vacuum polarization function Π(q) around q = 0 and using dispersion relations, the derivatives at q = 0 can be expressed as weighted integrals over the imaginary part of Π(q), which in turn is given by the cross section for electronpositron annihilation into hadrons. Let us denote the normalised cross section for heavy quark production as RQ(s) ≡ σQ(s)/σpoint(s). The moments of RQ, defined as
15450828
Recent progress in computing four-loop massive correlators
We report about recent progress in computing four-loop massive correlators. The expansion of these correlators in the external momentum leads to vacuum integrals. The calculation of these vacuum integrals can be used to determine Taylor expansion coefficients of the vacuum polarization function and decoupling functions in perturbative Quantum chromodynamics. New results at four-loop order for the lowest Taylor expansion coefficient of the vacuum polarization function and for the decoupling relation are presented.