A.D. Liberman

Measurements of e+e− → e+e− →, e+e− → μ+μ− and e+e− → γγ at Center of Mass Energies Close to 3105 MeV

We report here independent evidence for the decay of the recently discovered ψ(3105) particle1–3 into electron-positron pairs and new evidence for the decay of this particle into muon pairs. We also report the results of a measurement of the reaction e+e− → γγ at center of mass energies in the vicinity of 3105 MeV. These measurements were begun immediately following the discovery of the ψ(3105) at SPEAR1. At that time an apparatus primarily designed for the study of quantum electrodynamics (QED) was operating in the second interaction region at SPEAR and was applied immediately thereafter to the study of the ψ(3105). This apparatus is very similar to that described recently by Beron, et al.,4 and is capable of identifying the reactions e+e− → e+e− →, e+e− → μ+μ− and e+e− → γγ. The detection apertures and procedures used to recognize each of these reactions are identical to those described by Beron et al.,4 except that the detection aperture for the reaction e+e− → μ+μ− is larger by a factor of 2.6. All of the measurements reported in this letter were made with the detection apparatus set to accept particles produced at angles 6 close to 90° with respect to the colliding beams.

Measurements of the reaction e/sup +/e/sup -/. -->. mu. /sup +/. mu. /sup -/ at center-of-mass energies in the range 6. 2--7. 4 GeV

Measurements of the cross section for the muon-pair-annihilation reaction e/sup +/e/sup -/ ..-->.. ..mu../sup +/..mu../sup -/, relative to Bhabha scattering at 4/sup 0/, are reported at center-of-mass energies in the range 6.2--7.4 GeV. These measurements provide a fundamental test of quantum electrodynamics (QED) for timelike values of the invariant four-momentum transfer q/sup 2/ as high as 54.8 (GeV/c)/sup 2/, which in this reaction is carried by the photon propagator. The results are in agreement with predictions of QED.