55072533
Hadronic Freeze-Out in A+A Collisions meets the Lattice QCD Parton-Hadron Transition Line
We analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS and LHC energies. Employing the UrQMD hybrid transport model we study the effects of the final hadron/resonance expansion phase on the hadron multiplicities established at hadronization. The bulk meson yields freeze out directly at hadronization whereas the baryon-antibaryon sector is subject to significant alterations, due to annihilation and regeneration processes. We quantify the latter changes by survival factors for each species which are applied to modify the statistical model predictions for the data. The modified SM analysis recovers the hadronization points, which coincide with the recent lattice QCD predictions of the parton-hadron transition line at finite baryochemical potential.
119443576
High pT Spectra of Identified Particles Produced in Pb+Pb Collisions at 158 GeV/nucleon Beam Energy
Transverse momentum spectra of π ± , p , p ¯ , K ± , K s 0 and Λ at midrapidity were measured at high p T in Pb+Pb collisions at 158 GeV/nucleon beam energy by the NA49 experiment. Particle yield ratios ( p / π , K / π and Λ / K s 0 ) show an enhancement of the baryon/meson ratio for p T > 2 GeV / c . The nuclear modification factor R CP is extracted and compared to RHIC measurements and pQCD calculations.
120318226
Hadron ratio fluctuations in heavy-ion collisions
121064931
Exploring the phase diagram of strongly interacting matter; news from SPS and RHIC
Abstract Two experimental programs are aiming to study nuclear collisions in the energy regime 5 GeV ≤ s NN ≤ 20 GeV in order to explore an essential part of the phase diagram of strongly interacting matter. The programs are motivated by observations that indicate a phase transition to take place in this energy domain: the onset of deconfinement. The STAR collaboration proposes an energy scan in the Relativistic Heavy Ion Collider (RHIC) at BNL. The ongoing program of the NA61/SHINE experiment consists of a two-dimensional energy-system size scan in nuclear and elementary collisions. The goal of both programs is to study the properties of the onset of deconfinement and to eventually discover the conjectured critical point of strongly interacting matter. A comparison of the strengths and limitations reveals the complementarity of the two programs.
119462879
High pT spectra of identified particles produced in Pb+Pb collisions at 158 A GeV beam energy
Results of the NA49 collaboration on the production of hadrons with large transverse momentum in Pb+Pb collisions at 158 A GeV beam energy are presented. A range of up to pT = 4 GeV/c is covered. The nuclear modification factor RCP is extracted for π±, K± and p, and the baryon to meson ratios and Λ/K0s are studied. All results are compared to other measurements at SPS and RHIC and to theoretical calculations.
16599979
Global Properties of Nucleus-Nucleus Collisions
QCD as a theory of extended, strongly interacting matter is familiar from big bang evolution which, within the time interval from electro-weak decoupling (10−12 s) to hadron formation (5 × 10−6 s), is dominated by the expansion of quark–gluon matter, a color conducting plasma that is deconfined. In the 1970s deconfinement was predicted [1–5] to arise from the newly discovered “asymptotic freedom” property of QCD; i.e., the plasma was expected to be a solution of perturbative QCD at asymptotically high square momentum transfer Q 2, or temperature T
33472339
Gravitational corrections to Yukawa and phi{4} interactions.
We consider the lowest order quantum gravitational corrections to Yukawa and phi{4} interactions. Our results show that quantum gravity leads to contributions to the running coupling constants if the particles are massive and therefore alters the scaling behavior of the standard model. Furthermore, we find that the gravitational contributions to the running of the masses vanish.
2032681
All tree-level amplitudes in massless QCD
We derive compact analytical formulae for all tree-level color-ordered gauge theory amplitudes involving any number of external gluons and up to four massless quarkanti-quark pairs. A general formula is presented based on the combinatorics of paths along a rooted tree and associated determinants. Explicit expressions are displayed for the next-to-maximally helicity violating (NMHV) and next-to-next-to-maximally helicity violating (NNMHV) gauge theory amplitudes. Our results are obtained by projecting the previously-found expressions for the super-amplitudes of the maximally supersymmetric super Yang-Mills theory ($$ \mathcal{N} = 4 $$ SYM) onto the relevant components yielding all gluon-gluino tree amplitudes in $$ \mathcal{N} = 4 $$ SYM. We show how these results carry over to the corresponding QCD amplitudes, including massless quarks of different avors as well as a single electroweak vector boson. The public Mathematica package GGT is described, which encodes the results of this work and yields analytical formulae for all $$ \mathcal{N} = 4 $$ SYM gluon-gluino trees. These in turn yield all QCD trees with up to four external arbitrary-flavored massless quark-anti-quark pairs.
119223768
No Lee-Wick Fields out of Gravity
We investigate the gravitational one-loop divergences of the standard model in large extra dimensions, with gravitons propagating in the ($4+\ensuremath{\delta}$)-dimensional bulk and gauge fields as well as scalar and fermionic multiplets confined to a three-brane. To determine the divergences we establish a cutoff regularization which allows us to extract gauge-invariant counterterms. In contrast to the claim of a recent paper [F. Wu and M. Zhong, Phys. Rev. D 78, 085010 (2008).], we show that the fermionic and scalar higher derivative counterterms do not coincide with the higher derivative terms in the Lee-Wick standard model. We argue that even if the exact Lee-Wick higher derivative terms were found, as in the case of the pure gauge sector, this would not allow to conclude the existence of the massive ghost fields corresponding to these higher derivative terms in the Lee-Wick standard model.