JUN
27
Today
Nuclear Physics Seminar
"Measurement of longitudinal flow correlations in 2.76 and 5.02 TeV Pb+Pb collisions with the ATLAS detector"
Presented by Peng Huo, Stony Brook University
11 am, Small Seminar Room, Bldg. 510
Tuesday, June 27, 2017, 11:00 am
Hosted by: 'Jin Huang'
Longitudinal dynamics has recently become a topic of great interest in the study of ultra-relativistic heavy ion collisions. Measurement of the longitudinal fluctuations of the flow harmonic coefficients $v_n$ and event-plane angles $\Psi_n$ can provide a more complete picture of space-time evolution of the hot, dense medium formed in heavy ion collisions. Longitudinal flow decorrelations can be modeled with two contributions: magnitude fluctuations and event plane twist. However, existing observables do not separate these two effects. In this analysis, a new 4-particle correlator is used to separate the event-plane twist from magnitude fluctuations in 2.76 and 5.02 Pb+Pb collisions. Results show both effects have a linear dependence on pseudorapidity separation for $v_{2-5}$, and show a small but measurable variation with collision energy. The correlation of $\Psi_n $ of different order are also expected to have longitudinal fluctuations due to the non-linear mixing effects between lower and higher order flow harmonics. First measurement of such non-linear mode-mixing effects as a function of pseudorapidity is also presented. These result will help to constrain initial conditions along longitudinal direction and also help understand the longitudinal evolution of the fireball.
JUN
30
Friday
Nuclear Theory/RIKEN Seminar
"Probing Transverse Momentum Broadening in Heavy Ion Collisions"
Presented by Feng Yuan, LBL
2 pm, Small Seminar Room, Bldg. 510
Friday, June 30, 2017, 2:00 pm
Hosted by: 'Heikki Mantysaari'
In this talk, we will discuss the dijet azimuthal de-correlation in relativistic heavy ion collisions as an important probe of the transverse momentum broadening effects in heavy ion collisions. We take into account both the soft gluon radiation in vacuum associated with the Sudakov logarithms and the jet PT-broadening effects in the QCD medium. We find that the Sudakov effects are dominant at the LHC, while the medium effects can play an important role at RHIC energies. This explains why the LHC experiments have not yet observed sizable PT-broadening effects in the measurement of dijet azimuthal correlations in heavy ion collisions. Future investigations at RHIC will provide a unique opportunity to study the PT-broadening effects and help to pin down the underlying mechanism for jet energy loss in a hot and dense medium.