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

TL;DR

This paper proposes a method to measure proton electromagnetic form factors near the threshold using antiproton-deuteron annihilation, estimating cross sections and discussing experimental feasibility at the Panda facility.

Contribution

It introduces a novel approach to access proton form factors in the time-like region near threshold via antiproton-nucleus annihilation, with estimated cross sections and experimental considerations.

Findings

Estimated cross section near threshold is about 1 pb/MeV.

Feasibility of measurement at Panda is discussed.

Potential to explore proton form factors in new kinematic region.

Abstract

In the reaction of the antiproton-deuteron electromagnetic annihilation pbar + d --> e+e-n the value of the invariant mass M of the (e+e-) pair can be near or below the (pbar p) 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 (pbar p) threshold. We estimate the cross section dsigma(pbar + d --> e+e-n)/dM for an antiproton beam momentum of 1.5 GeV/c. We find that near the (pbar p) threshold this cross section is about 1 pb/MeV. The case of heavy nuclei target is also discussed. Elements of experimental feasibility are presented for the process pbar + d --> e+e-n in the context of the Panda project. We conclude that this process has a chance to be measurable at Panda.