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.
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.
126051003
Charged pion production in heavy ion collision at SIS energies
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.
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.
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.
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.
53579185
Higgs production and decay with a fourth Standard-Model-like fermion generation
State-of-the-art predictions for the Higgs-boson production cross section via gluon fusion and for all relevant Higgs-boson decay channels are presented in the presence of a fourth Standard-Model-like fermion generation. The qualitative features of the most important differences to the genuine Standard Model are pointed out, and the use of the available tools for the predictions is described. For a generic mass scale of 400−600 GeV in the fourth generation explicit numerical results for the cross section and decay widths are presented, revealing extremely large electroweak radiative corrections, e.g., to the cross section and the Higgs decay into WW or ZZ pairs, where they amount to about −50 % or more. This signals the onset of a non-perturbative regime due to the large Yukawa couplings in the fourth generation. An estimate of the respective large theoretical uncertainties is presented as well.
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.
119198729
Higgs Pseudo-Observables, Second Riemann Sheet and All That
The relation between physical observables measured at LHC and Tevatron and standard model Higgs pseudo-observables (production cross section and partial decay widths) is revised by extensively using the notion of the Higgs complex pole on the second Riemann sheet of the S-matrix. The extension of their definition to higher orders is considered, confronting the problems that arise when QED (QCD) corrections are included in computing realistic observables. Numerical results are presented for pseudo-observables related to the standard model Higgs boson decay and production. The relevance of the result for exclusion plots of the standard model Higgs boson for high masses (up to 600 GeV) is discussed. Furthermore, a recipe for the analytical continuation of Feynman loop integrals from real to complex internal masses and complex Mandelstam invariants is thoroughly discussed.