Robert L. Thews

Enhanced J/{psi} production in deconfined quark matter

In high energy heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven and the Large Hadron Collider at CERN, each central event will contain multiple pairs of heavy quarks. If a region of deconfined quarks and gluons is formed, a mechanism for additional formation of heavy quarkonium bound states will be activated. This is a result of the mobility of heavy quarks in the deconfined region, such that bound states can be formed from a quark and an antiquark that were originally produced in separate incoherent interactions. Model estimates of this effect for J/{psi} production at RHIC indicate that significant enhancements are to be expected. Experimental observation of such enhanced production would provide evidence for deconfinement unlikely to be compatible with competing scenarios.

Momentum spectra of charmonium produced in a quark-gluon plasma

We calculate rapidity and transverse momentum distributions of charmonium formed in high-energy heavy ion collisions from incoherent recombination of charm quarks. The results are very sensitive to the corresponding distributions of the charm quarks, and thus can serve as a probe of the state of matter produced in the heavy ion collision. At one extreme, we generate charm pair momenta directly from pQCD amplitudes, which are appropriate if one can neglect the interaction of the quarks with the medium. At the other extreme, we generate momenta of charm quarks in thermal equilibrium with the expanding medium, appropriate for an extremely strong interaction. Explicit predictions are made for J/{psi} formation in Au-Au interactions at the BNL Relativistic Heavy Ion Collider. We find that for the case in that charm quark momenta are unchanged from the pQCD production calculation, both the rapidity and transverse momentum spectra of the formed J/{psi} are substantially narrower than would be anticipated in scenarios that do not include the in-medium formation. In particular, the average transverse momentum of the J/{psi} will exhibit a nonmonotonic behavior in the progression from pp to pA to AA interactions.

PRODUCTION OF DRELL-YAN PAIRS IN pp COLLISIONS

We compute cross sections for the Drell-Yan process in N-N collisions at next-to-leading order in αs. The mass, rapidity, transverse momentum, and angular dependence of these cross sections are presented. An estimate of higher order corrections is obtained from next-to-next-to-leading order calculation of the mass distribution. We compare the results with some of the existing data to show the quality of the agreement between calculations and data. We present predictions for energies that will become available at the RHIC and LHC colliders. Uncertainties in these predictions due to choices of scale, scheme and parton distribution are discussed.We compute cross sections for the Drell-Yan process in N--N collisions at next-to-leading order in

Quarkonium Formation Time in a Model-Independent Approach

\alpha_s

Domain structure of a disoriented chiral condensate from a wavelet perspective

. The mass, rapidity, transverse momentum, and angular dependence of these cross sections are presented. An estimate of higher order corrections is obtained from next-to-next-to-leading order calculation of the mass distribution. We compare the results with some of the existing data to show the quality of the agreement between calculations and data. We present predictions for energies which will become available at the RHIC and LHC colliders. Uncertainties in these predictions due to choices of scale, scheme and parton distribution are discussed.

Quarkonium formation at high energy

We use dispersion relations to reconstruct, in a model–independent way, the formation dynamics of heavy quarkonium from the experimental data on e + e − → ¯ QQ annihilation. We extract a distribution of formation times with a mean value for the J/ , = 0.44 fm; and for the �, = 0.32 fm. The corresponding widths of these distributions are given by �� J/ = 0.31 fm and ��� = 0.28 fm. This information can be used as an input in modeling of heavy quarkonium production on nuclear targets.

Bc-meson production in ultrarelativistic nuclear collisions

We present a novel method for studying the formation of a disoriented chiral condensate (DCC) in high energy heavy-ion collisions utilizing a discrete wavelet transformation. Because of its salient feature of space-scale locality, the discrete wavelet proves to be very effective in probing physics simultaneously at different locations in phase space and at different scales. We show that the probability distributions of the neutral pion fraction for various rapidity-bin sizes have distinctive shapes in the case of a DCC and exhibit a delay in approaching the Gaussian distribution required by the central limit theorem. We find the wavelet power spectrum for a DCC to exhibit a strong dependence on the scale while an equilibrium system and the standard dynamical models such as hijing have a flat spectrum.

J/Ψ production at RHIC in a QGP

The production of quarkonium in heavy ion collisions is studied at RHIC and LHC energies. General arguments indicate that, due to initial production of multiple quark pairs in each central collision, the final population of quarkonium may exhibit significant enhancements over straightforward extrapolation of behavior at SPS energy. Explicit calculations based on both a statistical hadronization picture and a kinetic formation mechanism in a deconfined state verify these general expectations. Such enhancements will alter the nature of how quarkonium yields may be used as a signature of deconfinement.

B_c Meson Production in Nuclear Collisions at RHIC

We study quantitatively the formation and evolution of B_c bound states in a space-time domain of deconfined quarks and gluons (quark-gluon plasma, QGP). At the Relativistic Heavy Ion Collider (RHIC) one expects for the first time that typical central collisions will result in multiple pairs of heavy (in this case charmed) quarks. This provides a new mechanism for the formation of heavy quarkonia which depends on the properties of the deconfined region. We find typical enhancements of about 500 fold for the B_c production yields over expectations from the elementary coherent hadronic B_c-meson production scenario. The final population of bound states may serve as a probe of the plasma phase parameters.

A review of the η-η′ mixing problem

In central collisions at RHIC, the initial production of heavy quarks will for the first time yield multiple pairs of c-cbar in each central event. If a region of deconfined quarks and gluons is subsequently formed, a new mechanism for the formation of heavy quarkonium bound states will be activated. This will result from the mobility of heavy quarks in the deconfined region, such that bound states can be formed from a quark and an antiquark which were originally produced in separate incoherent interactions. Our model estimates of this effect predict a dramatic increase in the number of observed J/Psi at RHIC, over that predicted from extrapolation of color-screening or gluon dissociation mechanisms from the lower CERN-SPS energies. The centrality and energy dependence of this effect should be readily observable by the Star and Phenix detectors. Thus the J/Psi abundance at RHIC will continue to provide a signature of QGP formation. However, it is in this environment a more useful probe, since contrary to prior expectations this large predicted J/Psi abundance should be relatively easy to measure.