116139290
Improving the precision of light quark mass determinations
We discuss the concepts and the framework of the renormalization procedure in regularization-invariant momentum subtraction schemes. These schemes are used in the context of lattice simulations for the determination of physical quantities like light quark masses. We focus on the renormalization procedure with a symmetric subtraction point of a quark mass and discuss its conversion from the RI/SMOM scheme to the MSbar scheme. A symmetric subtraction point allows for a lattice calculation with a reduced contamination from infrared effects. The perturbative series for the resulting matching factor at next-to-leading order is better behaved for the symmetric momentum configuration than for the exceptional one which can decrease the uncertainty in light quark mass determinations.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.