The Spectator Electromagnetic Effect on Charged Pion Spectra in Peripheral Ultrarelativistic Heavy-Ion Collisions

Abstract

We estimate the electromagnetic effect of the spectator charge on the momentum spectra of ${\pi }^{+}$ and ${\pi }^{-}$ produced in peripheral Pb+Pb collisions at SPS energies. We find that the effect is large and results in strongly varying structures in the $x_F$ dependence of the ${\pi }^{+}/{\pi }^{-}$ ratio, especially at low transverse momenta where a deep valley in the above ratio is predicted at $x_F\sim$ 0.15 -- 0.20. It appears that the effect depends on initial conditions. Thus, it provides new information on the space and time evolution of the non-perturbative pion creation process.

Comments: 20 pages and 8 figures