Sean Gavin

Long range correlations and the soft ridge in relativistic nuclear collisions

Relativistic Heavy Ion Collider experiments exhibit correlations peaked in relative azimuthal angle and extended in rapidity. Called the ridge, this peak occurs both with and without a jet trigger. We argue that the untriggered ridge arises when particles formed by flux tubes in an early Glasma stage later manifest transverse flow. Combining a blast wave model of flow fixed by single-particle spectra with a simple description of the Glasma, we find excellent agreement with current data.

HADRONIC J/PSI SUPPRESSION IN ULTRARELATIVISTIC NUCLEAR COLLISIONS

Abstract One of the proposed signatures of quark-gluon plasma formation in ultrarelativistic nuclear collisions is a suppression of J ψ production. We show that a similar reduction in the J/ψ signal can occur due to inelastic scattering of J/ψs in a hadronic resonance gas. This collisional suppression can be substantial, provided that the hadronic densities are as large as the first CERN data suggest.

Methods for the study of particle production fluctuations

We discuss various measures of net charge (conserved quantities) fluctuations proposed for the identification of critical phenomena in heavy ion collisions. We show the dynamical component of fluctuations of the net charge can be expressed simply in terms of integrals of two- and singleparticle densities. We discuss the dependence of the fluctuation observables on detector acceptance, detection efficiency and colliding system size and collisioncentrality. Finally, we present a toy model of particle production including charge conservation and resonance production to gauge the effects of such resonances and finite acceptance on the net charge fluctuations.

Charmonium Suppression by Comover Scattering in Pb+Pb Collisions

Experiment NA50 has reported an abrupt decrease inψproduction in Pb+Pb collisionsat 158GeV per nucleon[1]. Specifically, the collaboration presented a striking‘threshold effect’ in the ψ–to–continuum ratio by plot-ting it as a function of a calculated quantity, the meanpath length of the ψthrough the nuclear medium, L, asshown in fig. 1a. This apparent threshold has sparkedconsiderable excitement as it may signal the formationof quark–gluon plasma in the heavy Pb+Pb system [2].5 10 15

How to make large domains of disoriented chiral condensate

Rajagopal and Wilczek have proposed that relativistic nuclear collisions can generate domains in which the chiral condensate is disoriented. If sufficiently large (i.e., nucleus sized), such domains can yield measurable fluctuations in the number of neutral and charged pions. However, by numerical simulation of the zero-temperature two-flavor linear sigma model, we find that domains are essentially [ital pion] sized. Nevertheless, we show that large domains can occur if the effective mesons masses are much lighter.

Larger domains of disoriented chiral condensate through annealing

Abstract Relativistic heavy ion collisions can generate metastable domains in which the chiral condensate is disoriented. Nucleussizeddomains can yield measurable fluctuations in the number of neutral and charged pions. We propose a scenario in whichdomains are “annealed” by a dynamically evolving effective potential in the heavy ion system. Domains of sizes exceeding3 fm are possible in this scenario.

Effects of momentum conservation and flow on angular correlations observed in experiments at the BNL Relativistic Heavy Ion Collider

Correlations of azimuthal angles observed at RHIC have gained great attention due to the prospect of identifying fluctuations of parity-odd regions in the field sector of QCD. Whereas the observable of interest related to parity fluctuations involves subtracting opposite-sign from same-sign correlations, the STAR collaboration reported the same-sign and opposite-sign correlations separately. It is shown here how momentum conservation combined with collective elliptic flow contributes significantly to this class of correlations, though not to the difference between the oppositeand same-sign observables. The effects are modeled with a crude simulation of a pion gas. Though the simulation reproduces the scale of the correlation, the centrality dependence is found to be sufficiently different in character to suggest additional considerations beyond those present in the pion gas simulation presented here.

Antiproton Production as a Baryonometer in Ultrarelativistic Heavy Ion Collisions

Abstract We propose that measurements of the antiproton and proton yields in ultrarelativistic nucleus-nucleus collisions can provide a sensitive probe of the spacetime evolution in these reactions. We estimate the antiproton suppression expected due to annihilation processes for collisions in the energy range s =10–200 A GeV .

Pion interferometric tests of transport models

Abstract In hadronic reactions, the usual space-time interpretation of pion interferometry often breaks down due to strong correlations between spatial and momentum coordinates. We derive a general interferometry formula based on the Wigner density formalism that allows for arbitrary phase space and multiparticle correlations. Correction terms due to intermediate state pion cascading are derived using semiclassical hadronic transport theory. Finite wave packets are used to reveal the sensitivity of pion interference effects on the details of the production dynamics. The covariant generalization of the formula is shown to be equivalent to the formula derived via an alternate current ensemble formalism for minimal wave packets and reduces in the nonrelativistic limit to a formula derived by Pratt. The final expression is ideally suited for pion interferometric tests of Monte Carlo transport models. Examples involving gaussian and inside-outside phase space distributions are considered.

Causal diffusion and the survival of charge fluctuations in nuclear collisions

Diffusion may obliterate fluctuation signals of the QCD phase transition in nuclear collisions at SPS and RHIC energies. We propose a hyperbolic diffusion equation to study the dissipation of net charge fluctuations. This equation is needed in a relativistic context, because the classic parabolic diffusion equation violates causality. We find that causality substantially limits the extent to which diffusion can dissipate these fluctuations.