Proton Timelike Form Factors Near Threshold via Antiproton-Nucleus Electromagnetic Annihilation

Abstract

In the reaction of the antiproton-deuteron electromagnetic annihilation p + d → ne + e − the value of the invariant mass M e + e − of the e + e − pair can be near or below the pp mass even for enough high momentum of incident antiproton. This allows to access the proton electromagnetic form factors in the time-like region of q 2 near the pp threshold. We estimate the cross section dσ(p + d → e + e − n)/dM e + e − for an antiproton beam momentum of 1.5 GeV/c. We find that for values of M e + e − near the pp threshold this cross section is about 1 pb/MeV. The case of heavy nuclei 12 C, 56 Fe and 197 Au is also estimated. Elements of experimental feasibility are studied in the context of the PANDA project [1, 2]. We conclude that this process has a chance to be measurable at PANDA.