Bulletin of the American Physical Society
2015 Annual Spring Meeting of the APS Ohio-Region Section
Volume 60, Number 3
Friday–Saturday, March 27–28, 2015; Kent, Ohio
Session B2: Heavy Ion Theory I |
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Chair: Mauricio Martinez-Guerrero, Ohio State University Room: KSU Student Center 314 |
Friday, March 27, 2015 3:00PM - 3:15PM |
B2.00001: Subleading harmonic flows in hydrodynamic simulations of heavy ion collisions Aleksas Mazeliauskas, Derek Teaney We perform a Principal Component Analysis (PCA) of $v_3(p_T)$ in event-by-event hydrodynamic simulations of Pb+Pb collisions at the LHC. The PCA procedure identifies two dominant contributions to the two particle correlation function, which together capture 99.9\% of the squared variance. We find that the subleading flow (which is the largest source of flow factorization breaking in hydrodynamics) is predominantly a response to the radial excitations of a third-order eccentricity. We present a systematic study of the hydrodynamic response to these radial excitations in 2+1D viscous hydrodynamics. Finally, we construct a good geometrical predictor for the orientation angle and magnitude of the leading and subleading flows using two Fourier modes of the initial geometry. [Preview Abstract] |
Friday, March 27, 2015 3:15PM - 3:30PM |
B2.00002: Event-By-Event Fluctuations of HBT Radii and the QGP Shear Viscosity Christopher Plumberg, Ulrich Heinz One of the major lessons from the field of heavy-ion physics in the past several years has been the significance of the role played by event-by-event fluctuations in the evolution of a heavy-ion collision. Their effects on many observables (e.g., particle multiplicities, anisotropic flows, etc.) Have already been studied systematically, and many of the most interesting properties of their event-by-event distributions are well known. In this talk, i will discuss the motivation for extending the successes of this event-by-event paradigm to include the Hanbury-Brown---Twiss (HBT) radii derived from intensity interferometry. In particular, I will present a connection between the variance of an event-by-event HBT distribution and the value of the specific shear viscosity, eta/s, in the quark-gluon plasma. [Preview Abstract] |
Friday, March 27, 2015 3:30PM - 3:45PM |
B2.00003: Modeling Initial Conditions in Relativistic Ion Collisions Kevin Welsh When particles collide at relativistic speeds, they generate an exotic form of matter called quark gluon plasma. Currently, the only way to observe this type of matter in nuclear collisions is at particle accelerators, such as the Relativistic Heavy Ion Collider. The relative initial position and orientation of the colliding nuclei has a large influence on the anisotropies found in the plasma that evolves from it, and the initial orientation depends on everything from the energy of the nuclei to the internal structure of their nucleons, and there are aspects of the plasma evolution that remain undetermined. In order to improve the modeling of high energy particle collisions I study proton-gold collisions where previous evolution models fail to quantitatively describe the observed flow pattern. I have added sub-nucleonic structure and gluon field fluctuations to the energy density profiles created in nuclear collisions that we hope improves the description of proton-lead collisions. I show the effects of these fluctuations on the initial eccentricities that drive anisotropic flow of the QGP. I found increased ellipticity and triangularity which offer the chance to better reproduce the experimentally measured large elliptic and triangular flows seen in p+Pb collisions at the LHC. [Preview Abstract] |
Friday, March 27, 2015 3:45PM - 4:00PM |
B2.00004: Constraining the quark-gluon plasma viscosity with thermal photons Ulrich Heinz, Chun Shen, Jean-Francois Paquet, Charles Gale Because photons interact only electromagnetically, photons produced in high-energy heavy-ion collisions can escape from the fireball during all collision stages, especially from its hot core. Using state-of-the-art viscous hydrodynamic calculations with fluctuating initial conditions, it is demonstrated that by measuring the anisotropy of photons one may infer the viscosity of QCD matter independently from hadronic observables. For photons, viscous corrections to the emission rates are found to have a larger effect on the anisotropic flow coefficients than the viscous suppression of hydrodynamic flow anisotropies. It is pointed out that the ratio of elliptic to triangular flow, $v_2/v_3$, allows to discriminate between hydrodynamic and other suggested origins of the measured photon flow anisotropies. The spacetime regions which contribute dominantly to the photon flow anisotropies are identified, and interesting novel features of the directed flow $v_1$ of thermal photons for RHIC and LHC energies are explored. [Preview Abstract] |
Friday, March 27, 2015 4:00PM - 4:15PM |
B2.00005: Collision Geometry and Flow in U+U Collisions Andy Goldschmidt, Zhi Qiu, Chun Shen, Ulrich Heinz Using event-by-event viscous fluid dynamics to evolve fluctuating initial density profiles from the Monte-Carlo Glauber model for U+U collisions, we report a ``knee''-like structure in the elliptic flow as a function of collision centrality, located around the 0.5\% most central collisions as measured by the final charged multiplicity. This knee is due to the preferential selection of tip-on-tip collision geometries by a high-multiplicity trigger. Such a knee structure is not seen in the STAR data. This rules out the two-component MC-Glauber model for initial energy and entropy production. Hence an enrichment of tip-tip configurations by triggering solely on high-multiplicity in the U+U collisions does not work. On the other hand, using the Zero Degree Calorimeters (ZDCs) coupled with event-shape engineering, we identify the selection purity of body-body and tip-tip events in the full-overlap U+U collisions. By further constraining on the asymmetry of the ZDC signals, we increase the probability of selecting tip-tip events in U+U collisions. [Preview Abstract] |
Friday, March 27, 2015 4:15PM - 4:30PM |
B2.00006: Deconfinement and Percolation David Garand The initial moments of heavy ion collisions can be described through the creation of color strings stretched between the projectile and target. Particles produced in the collision are then formed via quark-antiquark pair emissions from the color field of the strings, in a process similar to the Schwinger Mechanism employed in QED. I will present the development of the Color String Percolation Model (CSPM), and some of the recent successes it has in matching data from experiment. I will discuss where the model can be modified, and which assumptions may lead to differences in final results. The CSPM may prove to be a useful tool for selecting upon events in future experiments, and there are already suggestions on how to directly apply it to data. [Preview Abstract] |
Friday, March 27, 2015 4:30PM - 4:45PM |
B2.00007: Viscous Effects on the Mapping of the Initial to Final State in Heavy Ion Collisions Jacquelyn Noronha-Hostler, Fernando Gardim, Matthew Luzum, Frederique Grassi We investigate the correlation between various aspects of the initial geometry of heavy ion collisions at the Relativistic Heavy Ion Collider energies and the final anisotropic flow, using v-USPhydro, a 2+1 event-by-event viscous relativistic hydrodynamical model. We test the extent of which shear and bulk viscosity affect the prediction of the final flow harmonics, $v_n$, from the initial eccentricities, $\varepsilon_n$. We investigate in detail the flow harmonics $v_1$ through $v_5$ where we find that $v_1$, $v_4$, and $v_5$ are dependent on more complicated aspects of the initial geometry that are especially important for the description of peripheral collisions, including a non-linear dependence on eccentricities as well as a dependence on shorter-scale features of the initial density. Furthermore, we compare our results to previous results from NeXSPheRIO, a 3+1 relativistic ideal hydrodynamical model that has a non-zero initial flow contribution, and find that the combined contribution from 3+1 dynamics and non-zero, fluctuating initial flow decreases the predictive ability of the initial eccentricities, in particular for very peripheral collisions, but also disproportionately in central collisions. [Preview Abstract] |
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