## Columbia-Baruch

## Nuclear Theory Seminars

Fall Semester 2015

Located at Columbia University in the seminar room in 425 Pupin Hall, 538 W 120th St, New York, NY 10027

Find Spring Semester 2015 here.

Dec 07, 2015

Initial state and early-time effects in p+A collisions

__Soeren Schlichting__

12:00 pm

A surprising discovery in high-energy proton-nucleus collisions at the LHC was the observation of pronounced azimuthal correlations. In this talk I will discuss recent progress in understanding how azimuthal correlations can be generated due to initial state and early time effects and critically examine the question to what extent experimentally observed correlations can be described by initial state physics.

Nov 16, 2015

Quest for anomaly-induced transport effects in heavy-ion collisions

__Yuji Hirono (Stony Brook)__

1:00 PM

Recently, it turned out that the chiral anomaly gives rise to

macroscopic transport phenomena. On such example is the chiral

magnetic effect(CME), which is a phenomenon that an electric current

is generated along an applied magnetic field. Those currents are

non-dissipative, and are naturally incorporated into hydrodynamic

equations, which are called anomalous hydrodynamics.

Theoretically, the CME should be happening in heavy-ion collisions.

The data reported by STAR and PHENIX collaborations at RHIC and ALICE

collaborations at the LHC show a behavior consistent with the CME, but

the quantitative understanding is still lacking. In order to reach a

definitive conclusion, a reliable theoretical tool that can describe

the charge-dependent observables is indispensable. In this talk, we

report our recent attempt of quantitative modeling of the CME for

heavy-ion collisions. Basing on the event-by-event hydrodynamic

simulations for hundreds of thousands of collisions, we calculate the

correlation functions that are measured in experiments, and discuss

how the anomalous transports affect the observables. If time allows, I

will also talk about the change of the topology of magnetic fields

caused by the chiral anomaly.

Nov 12, 2015

Fluctuations of harmonic and radial flow in heavy ion collisions with principal components

__Aleksas Mazeliauskas (Stony Brook)__

1:30 PM

In heavy ion collisions the wealth of experimental data allows us to decompose two-particle correlation function into Fourier harmonics and investigate their dependence on transverse momentum p_T. The failure of two-particle correlation function to factorize into single particle distributions indicates that there are multiple independent sources of collective flow in heavy ion collisions. In this talk I will present principal component analysis (PCA) as a tool to find the dominant contributions to the two-particle correlation function and I will show results for the analyzed spectrum of harmonic flow, v_n(p_T) for n=0-5, in event-by-event hydrodynamic simulations of Pb+Pb collisions at the LHC. We found that the subleading modes for v_0, v_1 and v_3 is a linear response to the radial excitation of the corresponding eccentricity. By contrast, for v_2 the subleading elliptic flow in peripheral collisions is dominated by the nonlinear mixing between the leading elliptic flow and radial flow fluctuations. Finally, I will compare our study with preliminary CMS results.

References:

1509.07492, 1501.03138

Nov 09, 2015

Recent Heavy Ion Results from the ATLAS Experiment

__Aaron Angerami (Columbia University)__

12:00 PM

This talk will present the latest measurements from the ATLAS Collaboration related to heavy-ion collisions. This includes a surprising new observation of elliptic modulation of particle production in pp collisions, an observation often associated with hydrodynamical behavior in nuclear collisions. The strength of this modulation shows a similar pT dependence as that observed in nuclear collisions, but shows remarkably little center-of-mass energy- and multiplicity dependence, which complicates the simple interpretation of quark-gluon-plasma formation in rare, high multiplicity nucleon-nucleon collisions. The implications of these results are discussed, specifically in the context of their impact on our understanding of the matter produced in nuclear collisions and its evolution. New measurements from p+Pb collisions are presented that constrain both the initial parton densities and nuclear geometry and yield insight into novel phenomena affecting the initial stages of the collisions. Finally, measurements of jets and heavy flavor production in Pb+Pb collisions are presented. These results provide the first experimental evidence that quarks and gluons experience different energy loss in the quark-gluon-plasma. I will discuss what can be learned from these jet measurements and how they fit in with a larger program to address key questions about the strong-coupling observed in heavy ion collisions.

Oct 19, 2015

Thermal photons from a modern hydrodynamical model of heavy ion collisions

__Jean-Francois Paquet (Stony Brook)__

Early fluid-dynamical calculations of direct photon spectra and momentum anisotropy were found to be systematically smaller than measurements from the RHIC and the LHC, an observation that became known as the "direct photon puzzle". I will show that the use of a modern hydrodynamical model of heavy ion collisions and of the latest photon emission rates greatly improves agreement with both ALICE andPHENIX data, supporting the idea that thermal photons are the dominant source of direct photon momentum anisotropy in heavy ion collisions. The event-by-event hydrodynamical model used includes, for the first time, both shear and bulk viscosities, along with second order couplings between the two viscosities. Calculations using different photon emission rates will be shown, including one that takes into account the effect of confinement on photon emission. The effect of both shear and bulk viscosities on the photon rates will be shown to have a measurable effect on the photon momentum anisotropy.

Oct 05, 2015

Hydrodynamics and eta/s in Strongly Correlated Electron Systems

__Jon Rameau (BNL)__

Perfect fluids are characterized as having the smallest ratio of shear viscosity to entropy density, η/s, consistent with quantum uncertainty and causality. So far, nearly perfect fluids have only been observed in the quark-gluon plasma and in unitary atomic Fermi gases, exotic systems that are amongst the hottest and coldest objects in the known universe, respectively. We use angle resolved photoemission spectroscopy to measure the temperature dependence of an electronic analog of η/s in an optimally doped cuprate high-temperature superconductor, finding it too is a nearly perfect fluid around, and above, its superconducting transition temperature Tc.

Sep 21, 2015

New theoretical developments on search for QCD critical points

__Yi Yin (BNL)__

Fluctuations of conserved quantities are important indicators of QCD critical point. We have derived a set of equations describing the real time evolution of non-Gaussian fluctuations in QCD critical regime by taking both universal equilibrium properties and universal non-equilibrium physics into account. We have applied our equations to model Beam energy scan program in heavy-ion collision experiment and illustrate importance of memory effect on search for QCD critical point. Finally, I will discuss possible divergence of heavy quark diffusive constant near QCD critical point and its phenomenological importance.