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

In the reaction of the antiproton-deuteron electromagnetic annihi- lation ¯ p + d → ne + e − the value of the invariant mass Me+e− of the e + e − pair can be near or below themass even for enough high momentum of inci- dent 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 sec- tion dσ(¯ p + d → e + e − n)/dMe+e− for an antiproton beam momentum of 1.5 GeV/c. We find that for values of Me+e− near the ¯ pp threshold this cross sec- tion 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.