DLS Information

The Dilepton Spectrometer

The DLS collaboration from early 1987 until the closure of the Bevalac, carried out a systematic study of e+e- production as a function of mass and energy. The DLS results, about 30k pairs, represent the world's only e+e- data at Bevalac/SIS energies. Important results include: 1) existence of a dielectron signal in both p-p and A-A collisions, 2) observation of contributions from mesonic decays (pi-zero, eta, rho/omega), bremsstrahlung and Delta/N* decays, 3) strong energy dependence of the pd/pp yield ratios signifying the presence of the eta-meson, 4) absolute value and shape of the mass spectrum at 5 GeV in p-p and p-d collisions shows need to modify existing N-N model calculations (pp vs. pn contributions, inelasticity), and 5) observation of high mass pairs (>500 MeV) in Ca-Ca collisions may be evidence for pionic annihilation. Analysis continues on the high statistics Ca-Ca studies and evolution of mass and pt-distributions with projectile/target mass.