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.
118724127
Hadronization and hadronic freeze-out in relativistic nuclear collisions
We analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS energies, employing the hybrid version of the Ultrarelativistic Quantum Molecular Dynamics model, which describes the transition from a hydrodynamic stage to hadrons by the Cooper-Frye mechanism, and matches to a final hadron-resonance cascade. We fit the results both before and after the cascade stage using the Statistical Model, to assess the effect of the cascade phase. We observe a strong effect on antibaryon yields except anti-Omega, resulting in a shift in T and mu_B of the freeze-out curve. We discuss indications of a similar effect in SPS and RHIC data, and propose a method to recover the bulk hadron freeze-out conditions.
119279250
Validity of the hadronic freeze-out curve
We analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS energies, employing the hybrid version of UrQMD which models hadronization from a hydrodynamic phase by the Cooper–Frye mechanism, and matches to a final hadron-resonance cascade. We fit the results both before and after the cascade stage using the statistical hadronization model to assess the effect of the cascade phase. We observe a strong effect on antibaryon yields except anti-Ω, resulting in a shift in T and μB. We discuss the implications for the freeze-out curve.
120318226
Hadron ratio fluctuations in heavy-ion collisions
118004237
Hadron Formation and the Phase Diagram of QCD Matter
We investigate hadronic species freeze-out systematics in A+A collisions at low SPS energies, corresponding to a baryochemical potential above 300 MeV, analyzing NA49 hadron production data in the framework of the statistical hadronization model, and in the UrQMD hadronic transport model. Observing no deviation from universal grand canonical hadro-chemical equilibrium freeze-out, we argue that the observed hadronic freeze-out points should universally signal the boundary line of the hadronic phase in the QCD matter phase diagram.
120107314
Fluctuation signals and the critical point
We explore the potential of fluctuation measurements to investigate the properties of hot and dense matter created in relativistic heavy-ion collisions to investigate signals expected from the critical point and the first-order phase transition. Contrary to calculations in a grand canonical ensemble we combine the dynamics of the systems with the nonequilibrium propagation of the order parameter of chiral symmetry. We find an enhancement of the fluctuations of the order parameter at the phase transition. Furthermore, we study the effect of exact baryon charge conservation on the net-baryon and the net-proton kurtosis for central (b ? 2.75 fm) Pb+Pb/Au+Au collisions from Elab = 2A GeV to GeV from the UrQMD model. The results are compared to experimentally applied cuts and corrections.
119250225
Comparing efficient computation methods for massless QCD tree amplitudes: Closed analytic formulas versus Berends-Giele recursion
Recent advances in our understanding of tree-level QCD amplitudes in the massless limit exploiting an effective (maximal) supersymmetry have led to the complete analytic construction of tree-amplitudes with up to four external quark-anti-quark pairs. In this work we compare the numerical efficiency of evaluating these closed analytic formulae to a numerically efficient implementation of the Berends-Giele recursion. We compare calculation times for tree-amplitudes with parton numbers ranging from 4 to 25 with no, one, two and three external quark lines. We find that the exact results are generally faster in the case of MHV and NMHV amplitudes. Starting with the NNMHV amplitudes the Berends-Giele recursion becomes more efficient. In addition to the runtime we also compared the numerical accuracy. The analytic formulae are on average more accurate than the off-shell recursion relations though both are well suited for complicated phenomenological applications. In both cases we observe a reduction in the average accuracy when phase space configurations close to singular regions are evaluated. We believe that the above findings provide valuable information to select the right method for phenomenological applications.