Method for measuring the charge radii of charged hyperons from the time-like region

Abstract

We propose a novel method for measuring the charge radii of charged stable hadrons, with which the first measurement of the charge radii of the Σ+ and the Ξ− is foreseen. The method explores the facts that the Dalitz decay ψ(2S)→YY¯e+e− contains the hyperon form factors and the lowest measurable four-momentum transfer squared can be as low as ∼4me2=1.05×10−6GeV2 in the time-like region. We identify a kinematic region where the hyperon form factors are essential and propose a method for subtracting the background from the data. It is estimated that the hyperon charge radii can be measured to a precision of about 0.2 fm with the BESIII experiment and one order of magnitude better at the future Super τ-Charm Facility. Moreover, the same method can be used to measure the charge radius of the proton, which provides an independent cross-check on the extraction of proton radius from elastic ep scattering or leptonic hydrogen spectroscopy.