Search for the direct production of positrons by 256- and 800-MeV protons

The invariant cross sections for direct positron production in p-p collisions have been measured to be Ed/sup 3/sigma/dp/sup 3/= (-3 +- 2) x 10/sup -32/ and (-14 +- 12) x 10/sup -32/ cm/sup 2//sr (GeV/c)/sup 2/ at 256 and 800 MeV, respectively. These results are consistent with zero (e/sup +//..pi../sup +/approximately-less-than3 x 10/sup -6/ at 800 MeV) and are in marked contrast to results at higher energies. (AIP)