Dilepton anisotropy from $p+Be$ and $Ca+Ca$ collisions at BEVALAC energies

Abstract

A full calculation of lepton-pair angular characteristics is carried out for $e^{+}{e}^{-}$ pairs created in $p+Be$ and $Ca+Ca$ collisions from 1.0 to 2.1 GeV/A. It is demonstrated that the dilepton decay anisotropy depends sensitively on the different sources and may be used for their disentangling. Due to the dominance of the $\eta$-and $\Delta$-Dalitz decays and only a small anisotropy coefficient for ${\pi }^{+}{\pi }^{-}$ annihilation, the expected anisotropy coefficients show a decrease with invariant mass of the dilepton pair and change only moderately when comparing $p+Be$ and $Ca+Ca$ reactions at the same bombarding energy.

Comments: 10 pages, LaTeX, plus 4 postscript figures tarred, compressed and uuencoded in separate file