A. H. Tang

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 〉 .

Parameterization of deformed nuclei for Glauber modeling in relativistic heavy ion collisions

The density distributions of large nuclei are typically modeled with a Woods-Saxon distribution characterized by a radius R-0 and skin depth a. Deformation parameters beta are then introduced to describe non-spherical nuclei using an expansion in spherical harmonics R-0(1 + beta Y-2(2)0 + beta Y-4(4)0). But when a nucleus is non-spherical, the R-0 and a inferred from electron scattering experiments that integrate over all nuclear orientations cannot be used directly as the parameters in the Woods-Saxon distribution. In addition, the beta(2) values typically derived from the reduced electric quadrupole transition probability B(E2)up arrow are not directly related to the beta(2) values used in the spherical harmonic expansion. B(E2). is more accurately related to the intrinsic quadrupole moment Q(0) than to beta(2). One can however calculate Q(0) for a given beta(2) and then derive B(E2). from Q(0). In this paper we calculate and tabulate the R-0, a, and beta(2) values that when used in a Woods-Saxon distribution, will give results consistent with electron scattering data. We then present calculations of the second and third harmonic participant eccentricity (epsilon(2) and epsilon(3)) with the new and old parameters. We demonstrate that epsilon(3) is particularly sensitive to a and argue that using the incorrect value of a has important implications for the extraction of viscosity to entropy ratio (eta/s) from the QGP created in Heavy Ion collisions

Antinuclei in Heavy-Ion Collisions

Abstract We review progress in the study of antinuclei, starting from Dirac’s equation and the discovery of the positron in cosmic-ray events. The development of proton accelerators led to the discovery of antiprotons, followed by the first antideuterons, demonstrating that antinucleons bind into antinuclei. With the development of heavy-ion programs at the Brookhaven AGS and CERN SPS, it was demonstrated that central collisions of heavy nuclei offer a fertile ground for research and discoveries in the area of antinuclei. In this review, we emphasize recent observations at Brookhaven’s Relativistic Heavy Ion Collider and at CERN’s Large Hadron Collider, namely, the antihypertriton and the antihelium-4, as well as measurements of the mass difference between light nuclei and antinuclei, and the interaction between antiprotons. Physics implications of the new observations and different production mechanisms are discussed. We also consider implications for related fields, such as hypernuclear physics and space-based cosmic-ray experiments.

Method for determining event-by-event elliptic flow fluctuations based on the first-order event plane in heavy-ion collisions

A new method is presented for determining event-by-event fluctuations of elliptic flow, v{sub 2}, using first-order event planes. By studying the event-by-event distributions of v{sub 2} observables and first-order event-plane observables, average flow and event-by-event flow fluctuations can be separately determined, making appropriate allowance for the effects of finite multiplicity and nonflow. The method has been tested with Monte Carlo simulations. The connection between flow fluctuations and fluctuations of the initial-state participant eccentricity is discussed.