Abstract
We calculate the production of dileptons and photons in the presence of a nontrivial Polyakov loop in QCD. This is applicable to the semi-Quark Gluon Plasma (QGP), at temperatures above but near the critical temperature for deconfinement. The Polyakov loop is small in the semi-QGP, and near unity in the perturbative QGP. Working to leading order in the coupling constant of QCD, we find that there is a mild enhancement, ~ 20%, for dilepton production in the semi-QGP over that in the perturbative QGP. In contrast, we find that photon production is strongly suppressed in the semi-QGP, by about an order of magnitude, relative to the perturbative QGP. In the perturbative QGP photon production contains contributions from 2->2 scattering and collinear emission with the Landau- Pomeranchuk-Migdal (LPM) effect. In the semi-QGP we show that the two contributions are modified differently. The rate for 2->2 scattering is suppressed by a factor which depends upon the Polyakov loop. In contrast, in an SU(N) gauge theory the collinear rate is suppressed by 1/N, so that the LPM effect vanishes at infinite N. To leading order in the semi-QGP at large N, we compute the rate from 2->2 scattering to the leading logarithmic order and the collinear rate to leading order.
Highlights
In many ways, the collisions of heavy ions at high energies appear to be well described by thermal properties of a Quark-Gluon Plasma (QGP)
With E T, we have shown that the ratio of photon production in the semi-Quark Gluon Plasma (QGP), to that in the perturbative QGP, is just the ratio of the thermal quark masses squared, summed over color: fγ(Q) =
The dilepton production rate was found to be slightly enhanced in the confined phase due to a cancellation in the phases of the statistical distribution functions for the quark and antiquark [98]
Summary
The collisions of heavy ions at high energies appear to be well described by thermal properties of a Quark-Gluon Plasma (QGP). In contrast to the naive expectation above, we find a mild enhancement of dilepton production in the semi-QGP, even into the confined phase This is because for an off-shell photon, it can proceed directly through a color singlet channel, a quark anti-quark pair. The leading contribution is from a 2 to 2 scattering, which includes the Compton scattering of a quark with a gluon and the pair annihilation of a quark anti-quark pair These particles can form a color singlet like the case of the dilepton production, but for an SU(N ) gauge theory, the ratio of the color singlet state to the number of all the states is suppressed by 1/N 2 at large N.
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