194 research outputs found

### Elliptic flow of thermal photons and formation time of quark gluon plasma at RHIC

We calculate the elliptic flow of thermal photons from Au+Au collisions at
RHIC energies for a range of values for the formation time $\tau_0$ but fixed
entropy (or particle rapidity density). The results are found to be quite
sensitive to $\tau_0$. The $v_2$ for photons decreases as $\tau_0$ decreases
and admits a larger contribution from the QGP phase which has a smaller $v_2$.
The elliptic flow coefficient for hadrons, on the other hand, is only
marginally dependent on $\tau_0$.Comment: 2 extra figures and discussion added. To appear in Physical Review C
(Rapid Communication

### Azimuthal flow of decay photons in relativistic nuclear collisions

An overwhelming fraction of photons from relativistic heavy ion collisions
has its origin in the decay of $\pi^0$ and $\eta$ mesons. We calculate the
azimuthal asymmetry of the decay photons for several azimuthally asymmetric
pion distributions. We find that the $k_T$ dependence of the elliptic flow
parameter$v_2$ for the decay photons closely follows the elliptic flow
parameter $v_2^{\pi^0}$ evaluated at $p_T \approx k_T+\delta$, where
$\delta\approx$ 0.1 -- 0.2 GeV, for typical pion distributions measured in
nucleus-nucleus collisions at relativistic energies. Similar results are
obtained for photons from the 2-$\gamma$ decay of $\eta$ mesons. Assuming that
the flow of $\pi^0$ is similar to those for $\pi^+$ and $\pi^-$ for which
independent measurements would be generally available, this ansatz can help in
identifying additional sources for photons. Taken along with quark number
scaling suggested by the recombination model, it may help to estimate $v_2$ of
the parton distributions in terms of azimuthal asymmetry of the decay photons
at large $k_T$.Comment: 6 pages, figures added, references added, with more elaborate
discussion

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