Bulletin of the American Physical Society
Spring 2013 Meeting of the APS Ohio-Region Section
Volume 58, Number 2
Friday–Saturday, March 29–30, 2013; Athens, Ohio
Session E1: Nuclear Theory II |
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Chair: Daniel Phillips, Ohio University Room: Grover Hall E205 |
Saturday, March 30, 2013 11:00AM - 11:12AM |
E1.00001: Hydrodynamic event-plane correlations in Pb+Pb collisions at LHC Zhi Qiu, Ulrich Heinz The correlations among event-plane angles measured by the ATLAS collaboration are compared to those from event-by-event viscous hydrodynamic simulations. The results show that the event-plane correlations are rooted in mode-coupling effects during the non-linear hydrodynamic evolution of the fireballs. These mix harmonic deformations of different orders, and this manifests itself in certain correlation patterns among the final flow angles that cannot be directly explained from correlations among the so-called participant plane angles in the initial state. Hydrodynamic evolution of the initial state into the experimentally observed final state is therefore necessary to understand the experimental data. It is also shown that the strength of the observed correlation is sensitive to the specific shear viscosity of the expanding fireball medium. When taken together with other observables, event-plane correlations thus impose constraints on both the initial state fluctuation spectrum and the transport coefficients of the quark-gluon plasma created in ultra-relativistic heavy-ion collision. [Preview Abstract] |
Saturday, March 30, 2013 11:12AM - 11:24AM |
E1.00002: Thermal photon emission from nearly equilibrated relativistic heavy-ion collisions Chun Shen, Charles Gale, Ulrich Heinz Photons are believed to be clean and penetrating probes of the medium created in ultra-relativistic heavy-ion collisions. The thermal photon spectra and their anisotropy are known to be very sensitive to the thermalization time, the specific shear viscosity, the equation of state of produced matter, and the initial state fluctuations [1]. Previous computations of photon emission spectra have been mostly carried out in a fully thermalized and chemical equilibrated medium evolving dynamically under the influence of an equation of state with a first order phase transition. But in realistic hydrodynamic simulations, the evolving system always slightly deviates from thermal equilibrium. In the hadronic phase, it also breaks the chemical equilibrium due to its fast expansion rate. In this work, we study how the off-thermal equilibrium and partial chemical equilibrium in the hadronic phase affect the yields and the azimuthal anisotropies of produced thermal photons in heavy-ion collisions at RHIC energy. We compare our calculations with measurements by the PHENIX experiment. \\[4pt] [1] M. Dion, J. F. Paquet, B. Schenke, C. Young, S. Jeon and C. Gale, ``Viscous photons in relativistic heavy ion collisions,'' Phys. Rev. C 84, 064901 (2011) [Preview Abstract] |
Saturday, March 30, 2013 11:24AM - 11:36AM |
E1.00003: Sign Flip of Single Transverse Spin Asymmetries in Drell-Yan and DIS: The Role of Cuts and Complex Phases Matthew Sievert, Stanley Brodsky, Dae Sung Hwang, Yuri Kovchegov, Ivan Schmidt The transverse polarization of a hadron's spin can couple to its partons' transverse momentum distribution, resulting in an asymmetry known as the Sivers asymmetry. Depending on the scattering mechanism, this asymmetry of the parton distribution may persist into the final-state hadron distribution. Such single transverse spin asymmetries provide unique insights into the internal spin structure of hadrons and can couple to different scattering processes than the usual unpolarized cross-section. One hallmark prediction of transverse-momentum-dependent factorization is that the Sivers asymmetry should have equal magnitude and opposite sign between the Drell-Yan process and semi-inclusive deep inelastic scattering. We explicitly verify this prediction in greater detail than had previously been considered, using a toy model for the proton wave function. With an explicit representation of the transverse spinors, we demonstrate how $C/P/T$ invariance couples the asymmetry to the imaginary part, or cut, of the diagrams. To establish the validity of the predicted sign flip, we demonstrate a non-trivial equivalence between the cuts present in deep inelastic scattering and the Drell-Yan process. [Preview Abstract] |
Saturday, March 30, 2013 11:36AM - 11:48AM |
E1.00004: Resummed Thermodynamics at Finite Temperature and Density Michael Strickland I will present the result of a calculation of the finite temperature thermodynamic functions of a quark-gluon plasma for general $N_c$ and $N_f$ to three-loop order using hard-thermal-loop perturbation theory. At this order, all ultraviolet divergences can be absorbed into renormalizations of the vacuum energy, the HTL mass parameters, and the strong coupling constant. I will show that at three loops, the results for the pressure, energy density, entropy density, and the trace anomaly are in very good agreement with lattice data down to temperatures $T > 2\,T_c$. In addition, I will present results of a recent two-loop calculation at finite temperature and chemical potential utilizing the same framework. [Preview Abstract] |
Saturday, March 30, 2013 11:48AM - 12:00PM |
E1.00005: Pion-pion scattering in $\chi$PT$_S$ Arbin Thapaliya, Daniel Phillips Starting from a version of the SU(2) chiral $\chi$PT Lagrangian that includes an explicit scalar-isoscalar field [1], we construct the amplitude for $\pi \pi$ scattering from threshold through the energies at which the $\sigma$ resonance affects the phase shifts. We exhibit a power counting which mandates the resummation of the one-loop self-energy of the scalar field to all orders in the s-channel. We employ a Dyson equation for this purpose and discuss the associated renormalization of the scalar field's mass parameter and field strength. We also display the prediction for the decay width of the resonance. The full $\pi \pi$ LO amplitude in the region of interest then includes the resonant s-channel amplitude, combined with t- and u-channel exchanges of the scalar and the standard LO $\chi$PT contact term. At threshold, the presence of the additional degree of freedom modifies the $\chi$PT prediction for the $\pi \pi$ scattering lengths [1]. We perform a partial-wave decomposition of this amplitude, identify the phase shifts in the kinematic domain up to the resonance peak, and compare them to recent accurate data for the s-wave isoscalar $\pi \pi$ phase shifts.\\[4pt] [1] J.~Soto, P.~Talavera and J.~Tarrus, Nucl.\ Phys.\ B {\bf 866}, 270 (2013). [Preview Abstract] |
Saturday, March 30, 2013 12:00PM - 12:12PM |
E1.00006: Similarity Renormalization Group Evolution of Three-Nucleon Forces in a Hyper-Spherical Plane-Wave Basis Kyle Wendt A permutationally consistent framework for computing the Similarity Renormalization Group (SRG) evolution of three-nucleon forces using hyperspherical harmonic (HH) plane waves is presented. The use of antisymmetric HH plane waves ensures unitary in a manner comparable to prior antisymmetric harmonic oscillator SRG evolutions while keeping many of the advantages of recent momentum space evolutions; that is, deviations from unitary are determined by the precision of the ODE solver and not by a basis truncation. Unitary equivalence is demonstrated for the triton using several chiral two- plus three-nucleon interactions. This approach has an additional advantage over previous methods in that it allows for a clean visualization of the evolution of the three-nucleon forces, which manifests the decoupling pattern and low-momentum universality. [Preview Abstract] |
Saturday, March 30, 2013 12:12PM - 12:24PM |
E1.00007: Long-Range Rapidity Correlations in Heavy-Light Ion Collisions Douglas E. Wertepny, Yuri V. Kovchegov We study two-particle long-range rapidity correlations arising in the early stages of heavy ion collisions in the saturation/Color Glass Condensate framework. We calculate the two-gluon production cross section while including all-order saturation effects in the heavy nucleus with the lowest-order rescattering in the lighter nucleus. We find four types of correlations in the two-gluon production cross section: (i) geometric correlations, (ii) HBT correlations accompanied by a back-to-back maximum, (iii) away-side correlations, and (iv) near-side azimuthal correlations which are long-range in rapidity. The geometric correlations (i) are due to the fact that nucleons are correlated by simply being confined within the same nucleus. Long-range rapidity correlations (iii) and (iv) have exactly the same amplitudes along with azimuthal and rapidity shapes: one centered around $\Delta \phi =\pi$ with the other one centered around $\Delta \phi =0$ (here $\Delta \phi$ is the azimuthal angle between the two produced gluons). We thus observe that the early-time CGC dynamics in nucleus-nucleus collisions generates azimuthal non-flow correlations which are qualitatively different from jet correlations by being long-range in rapidity. [Preview Abstract] |
Saturday, March 30, 2013 12:24PM - 12:36PM |
E1.00008: Marrying ab initio calculations and Halo-EFT: the case of ${}^7{\rm Li} + n \rightarrow {}^8{\rm Li} + \gamma$ Xilin Zhang, Kenneth M. Nollett, Daniel R. Phillips In this talk, we propose to combine the ab initio quantum-Monte-Carlo (QMC) calculation with the Halo-Effective-Field-Theory (Halo-EFT) framework, in order to study ${}^{7}{\rm Li}$ and ${}^7{\rm Be}$ radiative nucleon captures, which are relevant to astrophysics. In the low energy, they are sensitive to the shallow ground states of ${}^{8}{\rm Li}$ and ${}^{8}{\rm B}$ (being shallow as compared to ${}^{7}{\rm Li}$ and ${}^{7}{\rm Be}$ breakup energy). We can approximate ${}^{8}{\rm Li}$ (${}^{8}{\rm B}$) as composed of ${}^{7}{\rm Li}$ (${}^{7}{\rm Be}$) core and a neutron (proton) with an anomalously extended wave function. The scattering and bound states can be studied in Halo-EFT, in which both core and neutron are treated as fundamental degrees of freedom. However, the couplings in EFT are unknown. Meanwhile, the QMC calculation can provide valuable information about the bound and resonant states. So we use asymptotic normalization from QMC calculations to calibrate our EFT Lagrangian and then apply it to study radiative captures. In this talk, I will show our preliminary study of ${\rm Li}$ system, as the result of this ``marriage.'' The study of ${}^{8}{\it B}$ with extra complexity due to Coulomb interaction is under way and will be reported elsewhere in the future. [Preview Abstract] |
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