Speaker
Koichi Hattori
(RIKEN-BNL Research Center)
Description
Electromagnetic probes have been expected to be penetrating probes of the early-time dynamics and quark-gluon plasma. Indeed, the photon spectra measured in the recent RHIC and LHC experiments provide us with an opportunity to deepen understanding of the photon emission mechanism, as they have significantly larger anisotropies compared to theoretical estimates by the hydrodynamic modeling of the bulk properties, implying a missing photon production mechanism giving rise to the large anisotropy. This also implies that the sensible production mechanism should be able to provide a good amount of photons so the anisotropy survives in averaging over various photon sources.
We discuss a photon production mechanism associated with the fragmentation of jets of quarks and antiquarks. We show theoretical estimates of the photon yield obtained from a convolution of the phenomenological jet distribution and the photon emission rate by the bremsstrahlung after the hard parton scatterings at the impact of heavy-ion collisions.
Our estimate shows a significant photon yield in a few GeV transverse momentum range and a power low behavior. This transverse momentum dependence may be consistent with a recent observation that the photon spectra measured in distinct collision energies can be fitted by power low exponents and the saturation momentum which characterizes the energy scale before and just after the collisions [Klein-Boesing, McLerran, Phys. Lett. B 741 (2015)]. An implication from this observation is the early-time emission of photons before other scales come into play. As a possible interpretation of the early-time emission, we argue that the power low behavior of the phenomenological jet distribution with an infrared cutoff by the saturation momentum is taken over by the photon spectrum. We also discuss anisotropy of the photon spectrum due to the jet energy loss which captures the anisotropic spatial geometry of the matter.
Primary authors
Bjoern Schenke
(Brookhaven National Lab)
Koichi Hattori
(RIKEN-BNL Research Center)
Larry McLerran
(BNL)
