Measurement of $\hat{I}›$ baryon polarization in $e^{+}{e}^{-}\to \hat{I}›\bar{\hat{I}}›$ at $\sqrt{s}=3.773$ GeV

Abstract

Using a data sample of $\ddot{I}ˆ(3770)$ events collected with the BESIII detector at BEPCII corresponding to an integrated luminosity of 2.9 fb${}^{-1}$, we report a measurement of $\hat{I}›$ spin polarization in $e^{+}{e}^{-}\to \hat{I}›\bar{\hat{I}}›$ at $\sqrt{s}=3.773$ GeV. The significance of polarization is found to be 2$\ddot{I}ƒ$ including the systematic uncertainty, which implies a zero phase between the transition amplitudes of the $\hat{I}›\bar{\hat{I}}›$ helicity states. This phase can be interpreted in terms of psionic form factors, and is determined to be $\hat{I}”\hat{I}{¦}^{\hat{I}}¨$ = $\hat{I}{¦}^{\hat{I}}{¨}_E-\hat{I}{¦}^{\hat{I}}{¨}_M$ = $(71_{-46}^{+66}$ $\pm$ 5)${}^{\circ }$. Similarly, the ratio between the form factors is found to be $R^{\ddot{I}}ˆ$ = $|G^{\hat{I}}{¨}_E/G^{\hat{I}}{¨}_M|$ = $0.48_{-0.07}^{+0.12}$ $\pm$ 0.04. The first uncertainties are statistical and the second systematic.

8 pages, 9 figures, consistent with paper published in Phys. Rev. D (Letter) 105, L011101 (2022)