Sergei A. Voloshin

Radial and elliptic flow at RHIC: Further predictions

Using a hydrodynamic model, we predict the transverse momentum dependence of the spectra and the elliptic flow for different hadrons in Au+Au collisions at sqrt(s)=130 AGeV. The dependence of the differential and p{_}t-integrated elliptic flow on the hadron mass, equation of state and freeze-out temperature is studied both numerically and analytically.

Elliptic flow at large transverse momenta from quark coalescence

We show that hadronization via quark coalescence enhances hadron elliptic flow at large p(perpendicular) relative to that of partons at the same transverse momentum. Therefore, compared to earlier results based on covariant parton transport theory, more moderate initial parton densities dN/deta(b=0) approximately 1500-3000 can explain the differential elliptic flow v(2)(p(perpendicular)) data for Au+Au reactions at sqrt[s]=130 and 200A GeV from BNL RHIC. In addition, v(2)(p(perpendicular)) could saturate at about 50% higher values for baryons than for mesons. If strange quarks have weaker flow than light quarks, hadron v(2) at high p(perpendicular) decreases with relative strangeness content.

Parity violation in hot QCD: How to detect it

In a recent paper (hep-ph/0406125) Kharzeev argues for the possibility of P- and/or CP-violation effects in heavy-ion collisions, the effects that can manifest themselves via asymmetry in {pi}{sup {+-}} production with respect to the direction of the system angular momentum. Here we present an experimental observable that can be used to detect and measure the effects.

Chiral magnetic and vortical effects in high-energy nuclear collisions—A status report

The interplay of quantum anomalies with magnetic field and vorticity results in a variety of novel non-dissipative transport phenomena in systems with chiral fermions, including the quark-gluon plasma. Among them is the Chiral Magnetic Effect (CME) -- the generation of electric current along an external magnetic field induced by chirality imbalance. Because the chirality imbalance is related to the global topology of gauge fields, the CME current is topologically protected and hence non-dissipative even in the presence of strong interactions. As a result, the CME and related quantum phenomena affect the hydrodynamical and transport behavior of strongly coupled quark-gluon plasma, and can be studied in relativistic heavy ion collisions where strong magnetic fields are created by the colliding ions. Evidence for the CME and related phenomena has been reported by the STAR Collaboration at Relativistic Heavy Ion Collider at BNL, and by the ALICE Collaboration at the Large Hadron Collider at CERN. The goal of the present review is to provide an elementary introduction into the physics of anomalous chiral effects, to describe the current status of experimental studies in heavy ion physics, and to outline the future work, both in experiment and theory, needed to eliminate the existing uncertainties in the interpretation of the data.

Collective phenomena in non-central nuclear collisions

Recent developments in the field of anisotropic flow in nuclear collision are reviewed. The results from the top AGS energy to the top RHIC energy are discussed with emphasis on techniques, interpretation, and uncertainties in the measurements.

Flow analysis with cumulants: Direct calculations

Anisotropic flow measurements in heavy-ion collisions provide important information on the properties of hot and dense matter. These measurements are based on analysis of azimuthal correlations and might be biased by contributions from correlations that are not related to the initial geometry, so-called nonflow. To improve anisotropic flow measurements, advanced methods based on multiparticle correlations (cumulants) have been developed to suppress nonflow contribution. These multiparticle correlations can be calculated by looping over all possible multiplets, however, this quickly becomes prohibitively CPU intensive. Therefore, the most used technique for cumulant calculations is based on generating functions. This method involves approximations, and has its own biases, which complicates the interpretation of the results. In this paper we present a new exact method for direct calculations of multiparticle cumulants using moments of the flow vectors.

Transverse radial expansion in nuclear collisions and two particle correlations

Abstract At the very first stage of an ultra-relativistic nucleus–nucleus collision new particles are produced in individual nucleon–nucleon collisions. In the transverse plane, all particles from a single NN collision are initially located at the same position. The subsequent thermalization and transverse radial expansion of the system create strong position-momentum correlations and lead to characteristic rapidity, transverse momentum, and azimuthal correlations among the produced particles.

Elliptic flow in the Gaussian model of eccentricity fluctuations

Abstract We discuss a specific model of elliptic flow fluctuations due to Gaussian fluctuations in the initial spatial x and y eccentricity components { 〈 ( σ y 2 − σ x 2 ) / ( σ x 2 + σ y 2 ) 〉 , 〈 2 σ x y / ( σ x 2 + σ y 2 ) 〉 } . We find that in this model v 2 { 4 } , elliptic flow determined from 4-particle cumulants, exactly equals the average flow value in the reaction plane coordinate system, 〈 v RP 〉 , the relation which, in an approximate form, was found earlier by Bhalerao and Ollitrault in a more general analysis, but under the same assumption that v 2 is proportional to the initial system eccentricity. We further show that in the Gaussian model all higher order cumulants are equal to v 2 { 4 } . Analysis of the distribution in the magnitude of the flow vector, the Q-distribution, reveals that it is totally defined by two parameters, v 2 { 2 } , the flow from 2-particle cumulants, and v 2 { 4 } , thus providing equivalent information compared to the method of cumulants. The flow obtained from the Q-distribution is again v 2 { 4 } = 〈 v RP 〉 .

Ultra-relativistic nuclear collisions: Event shape engineering

Abstract The evolution of the system created in a high energy nuclear collision is very sensitive to the fluctuations in the initial geometry of the system. In this Letter we show how one can utilize these large fluctuations to select events corresponding to a specific initial shape. Such an “event shape engineering” opens many new possibilities in quantitative test of the theory of high energy nuclear collisions and understanding the properties of high density hot QCD matter.

Testing the Chiral Magnetic Effect with Central U + U Collisions

A quark interaction with topologically nontrivial gluonic fields, instantons and sphalerons, violates P and CP symmetry. In the strong magnetic field of a noncentral nuclear collision such interactions lead to the charge separation along the magnetic field, the so-called chiral magnetic effect (CME). Recent results from the STAR collaboration on charge dependent correlations are consistent with theoretical expectations for CME but may have contributions from other effects, which prevents definitive interpretation of the data. Here I propose to use central body-body U+U collisions to disentangle correlations due to CME from possible background correlations due to elliptic flow. Further, more quantitative studies can be performed with collision of isobaric beams.