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 ${\Sigma }^{+}$ and the ${\Xi }^{-}$ is foreseen. The method explores the facts that the Dalitz decay $\psi (2S)\to Y\bar{Y}{e}^{+}{e}^{-}$ contains the hyperon form factors and the lowest measurable four-momentum transfer squared can be as low as $\sim 4m_e^2=1.05\times 10^{-6}\mathrm{Ge}{\mathrm{V}}^2$ 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 BES\Rom{3} experiment and one order of magnitude better at the future Super $\tau$-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.

Comments: 10 pages, 6 figures; PLB accepted version