Understand
A quantitative evaluation of dilepton sources in heavy-ion reactions is performed taking into account both thermal and non-thermal production mechanisms.
- The hadronic thermal emission rate is based on an electromagnetic current-correlation function with a low-mass region (LMR, M \lsim 1 GeV) dominated by vector mesons (\rho, \omega, \phi) and an intermediate-mass region (IMR, 1 GeV \le M \le 3 GeV) characterized by (the onset of) a multi-meson continuum.
- A convolution of the emission rates over a thermal fireball expansion results in good agreement with experiment in the low-mass spectra, confirming the predicted broadening of the \rho meson in hadronic matter in connection with the prevalence of baryon-induced medium effects.
- The absolute magnitude of the LMR excess is mostly controlled by the fireball lifetime, which in turn leads to a consistent explanation of the dilepton excess in the IMR in terms of thermal radiation.