P. Petreczky

Heavy quarkonium physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

Heavy quark-antiquark free energy and the renormalized Polyakov loop

Abstract We calculate the colour averaged and colour singlet free energies of static quark–antiquark sources placed in a thermal gluonic heat bath. We discuss the renormalization of these free energies using the short distance properties of the zero temperature heavy quark potential. This leads to the definition of the renormalized Polyakov loop as an order parameter for the deconfinement phase transition of the SU(3) gauge theory which is well behaved in the continuum limit.

Quarkonium feed down and sequential suppression

About 40-50% of the quarkonium ground states J/psi (1S) and Y(1S) produced in hadronic collisions originate from the decay of higher excitations. In a hot medium, these higher states are dissociated at lower temperatures than the more tightly bound ground states, leading to a sequential suppression pattern. Using new finite temperature lattice results, we specify the in-medium potential between heavy quarks and determine the dissociation points of different quarkonium states. On the basis of recent Collider Detector at Fermilab (CDF) data on bottomonium production, we then obtain first predictions for sequential Y suppression in nuclear collisions.

Freeze-out Conditions in Heavy Ion Collisions from QCD Thermodynamics

We present a determination of freeze-out conditions in heavy ion collisions based on ratios of cumulants of net electric charge fluctuations. These ratios can reliably be calculated in lattice QCD for a wide range of chemical potential values by using a next-to-leading order Taylor series expansion around the limit of vanishing baryon, electric charge and strangeness chemical potentials. From a computation of up to fourth order cumulants and charge correlations we first determine the strangeness and electric charge chemical potentials that characterize freeze-out conditions in a heavy ion collision and confirm that in the temperature range 150 MeV ≤ T ≤ 170 MeV the hadron resonance gas model provides good approximations for these parameters that agree with QCD calculations on the 5%-15% level. We then show that a comparison of lattice QCD results for ratios of up to third order cumulants of electric charge fluctuations with experimental results allows us to extract the freeze-out baryon chemical potential and the freeze-out temperature.

QCD Phase Transition with Chiral Quarks and Physical Quark Masses

Tanmoy Bhattacharya, Michael I. Buchoff, 3 Norman H. Christ, H.-T. Ding, Rajan Gupta, Chulwoo Jung, F. Karsch, 7 Zhongjie Lin, R. D. Mawhinney, Greg McGlynn, Swagato Mukherjee, David Murphy, P. Petreczky, Chris Schroeder, R A. Soltz, P. M. Vranas, and Hantao Yin Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87544, USA Physics Division, Lawrence Livermore National Laboratory, Livermore CA 94550, USA Institute for Nuclear Theory, Box 351550, Seattle, WA 98195-1550, USA Physics Department, Columbia University, New York, NY 10027, USA Key Laboratory of Quark and Lepton Physics (MOE) and Institute of Particle Physics, Central China Normal University, Wuhan 430079, China Physics Department, Brookhaven National Laboratory,Upton, NY 11973, USA Fakultät für Physik, Universität Bielefeld, D-33615 Bielefeld, Germany

A lattice calculation of thermal dilepton rates

Using clover improved Wilson fermions we calculate thermal vector meson correlation functions above the deconfinement phase transition of quenched QCD. At temperatures 1.5 T-c and 3 T-c. they are found to differ by less than 15%, from that of a freely propagating quark-anti-quark pair. This puts severe constraints on the dilepton production rate and in particular rules out a strong divergence of the dilepton rate at low energies. The vector spectral function, which has been reconstructed using the Maximum Entropy Method, yields an enhancement of the dilepton rate over the Born rate of at most a factor two in the energy interval 4 less than or similar to omega/T less than or similar to 8 and suggests that the spectrum is cut-off at low energies by a thermal mass threshold of about (2-3)T

Screened perturbation theory

A new perturbative scheme is proposed for the evaluation of the free energy density of field theories at finite temperature. The screened loop expansion takes into account exactly the phenomenon of screening in thermal propagators. The approach is tested in the N-component scalar field theory at 2-loop level and also at 3-loop in the large-N limit. The perturbative series generated by the screened loop expansion shows much better numerical convergence than previous expansions generated in powers of the quartic coupling

String breaking and quarkonium dissociation at finite temperatures

Abstract Recent lattice studies of string breaking in QCD with dynamical quarks determine the in-medium temperature dependence of the heavy quark potential. Comparing this to the binding energies of different quarkonium states, we check if these can decay into open charm/beauty in a confined hadronic medium. Our studies indicate in particular that the χ c and the ψ ′xa0dissociate into open charm below the deconfinement point.

Strangeness at high temperatures: from hadrons to quarks

Appropriate combinations of up to fourth order cumulants of net strangeness fluctuations and their correlations with net baryon number and electric charge fluctuations, obtained from lattice QCD calculations, have been used to probe the strangeness carrying degrees of freedom at high temperatures. For temperatures up to the chiral crossover, separate contributions of strange mesons and baryons can be well described by an uncorrelated gas of hadrons. Such a description breaks down in the chiral crossover region, suggesting that the deconfinement of strangeness takes place at the chiral crossover. On the other hand, the strangeness carrying degrees of freedom inside the quark gluon plasma can be described by a weakly interacting gas of quarks only for temperatures larger than twice the chiral crossover temperature. In the intermediate temperature window, these observables show considerably richer structures, indicative of the strongly interacting nature of the quark gluon plasma.

Infinite temperature limit of meson spectral functions calculated on the lattice

We analyze the cutoff dependence of mesonic spectral functions calculated at finite temperature on Euclidean lattices with a finite temporal extent. In the infinite temperature limit we present analytic results for lattice spectral functions calculated with standard Wilson fermions as well as a truncated perfect action. We explicitly determine the influence of Wilson doublers on the high momentum structure of the mesonic spectral functions and show that this cutoff effect is strongly suppressed when using an improved fermion action.