2 research outputs found
Elliptic flow of thermal photons in relativistic nuclear collisions
We predict the transverse momentum (pT) dependence of elliptic flow of
thermal photons for Au+Au collisions at the Relativistic Heavy Ion Collider. We
model the system hydrodynamically, assuming formation of a thermalized
quark-gluon plasma at some early time, followed by cooling through expansion,
hadronization and decoupling. Photons are emitted throughout the expansion
history. Contrary to hadron elliptic flow, which hydrodynamics predicts to
increase monotonically with pT, the elliptic flow of thermal photons is
predicted to first rise and then fall again as pT increases. Photon elliptic
flow at high pT is shown to reflect the quark momentum anisotropy at early
times when it is small, whereas at low pT it is controlled by the much larger
pion momentum anisotropy during the late hadronic emission stage. An
interesting structure is predicted at intermediate pT ~ 0.4 GeV/c where photon
elliptic flow reflects the momenta and the (compared to pions) reduced v2 of
heavy vector mesons in the late hadronic phase.Comment: 4 pages, 4 figures. Amended Fig. 3 and corresponding discussion, with
complete explanation of the low-pT structure of photon elliptic flow around
pT=400 MeV/
Photon HBT interferometry for non-central heavy-ion collisions
Currently, the only known way to obtain experimental information about the
space-time structure of a heavy-ion collision is through 2-particle momentum
correlations. Azimuthally sensitive HBT interferometry (Hanbury Brown-Twiss
intensity interferometry) can complement elliptic flow measurements by
constraining the spatial deformation of the source and its time evolution.
Performing these measurements on photons allows us to access the fireball
evolution at earlier times than with hadrons. Using ideal hydrodynamics to
model the space-time evolution of the collision fireball, we explore
theoretically various aspects of 2-photon intensity interferometry with
transverse momenta up to 2 GeV, in particular the azimuthal angle dependence of
the HBT radii in non-central collisions. We highlight the dual nature of
thermal photon emission, in both central and non-central collisions, resulting
from the superposition of QGP and hadron resonance gas photon production. This
signature is present in both the thermal photon source function and the HBT
radii extracted from Gaussian fits of the 2-photon correlation function.Comment: 18 pages, 12 figure