BESIII results on time-like baryon form factors

Alaa Dbeyssi,A Denig,C.-F Redmer

doi:10.1051/epjconf/201921804002

Abstract

This contribution reports on the recent measurements of baryon electromagnetic form factors at the BESIII experiment in Beijing. The Beijing e+e − collider BEPCII is a double-ring symmetric collider running at $ \sqrt s $ between 2.0 and 4.6 GeV. Baryon electromagnetic form factors can be measured at BESIII in direct e+e−-annihilation and in initial state radiation processes. Based on the data collected by the BESIII detector at 12 center of mass energies between 2.23 and 3.67 GeV, the measured $ \mathop e\nolimits^ + \mathop e\nolimits^ - \to \mathop p\limits^ - p $ cross section and the time-like proton form factor are presented. Preliminary results from the analysis of the initial state radiation process $ \mathop e\nolimits^ + \mathop e\nolimits^ - \to \mathop p\limits^ - p\gamma $ using a data set of 7.408 fb−1 collected at center of mass energies between 3.773 and 4.6 GeV, are also shown. The cross sections for $ \mathop e\nolimits^ + \mathop e\nolimits^ - \to \mathop {\mathop \Lambda \nolimits_c^ - }\limits^ - \mathop \Lambda \nolimits_c^ + $ and $ \mathop e\nolimits^ + \mathop e\nolimits^ - \to \mathop \Lambda \limits^ - \Lambda $ are measured near threshold with unprecedented precision. Preliminary results on the first measurement of the ^c form factor ratio |GE|/|GM| are also given. Ongoing analysis based on the high luminosity energy scan from 2015 and from radiative return at different $ \sqrt s $ are also described.

Highlights

Electromagnetic form factors are fundamental quantities, which describe the distribution of the electric charges and magnetization within the hadrons
Due to the fact that annihilation of e+e− is mostly accompanied by emission of one or several photons from the initial state, the high luminosity collected at the e+e− collider experiments, allows for a complementary approach to the energy scan technique in hadron cross section measurements: events with initial state radiation (ISR) photons lead to a reduction of the invariant massroafwthiedeprroantogne-aonftqip2rboetolonwsy√stse.m, and allow for a measurement of the baryonic form factors
SIII allows the measurement of baryon form factors using the direct baryon pair productions and the initial state radiation processes

Summary

Introduction

Electromagnetic form factors are fundamental quantities, which describe the distribution of the electric charges and magnetization within the hadrons. The electromagnetic form factors of baryons can be measured in time-like e+e− ↔ B B using the energy region (momentum transfer scan technique, in which the q2 < 0) through the annihilation reacti√ons center of mass energy of the collider ( s) is varied systematically, and at each energy point a measurement of the associated cross section can be carried out. Due to the fact that annihilation of e+e− is mostly accompanied by emission of one or several photons from the initial state, the high luminosity collected at the e+e− collider experiments, allows for a complementary approach to the energy scan technique in hadron cross section measurements: events with ISR photons lead to a reduction of the invariant mass (oqv2e)roafwthiedeprroantogne-aonftqip2rboetolonwsy√stse.m, and allow for a measurement of the baryonic form factors. SIII allows the measurement of baryon form factors using the direct baryon pair productions and the initial state radiation processes

Measurements of proton form factors at BESIII

Hyperon form factors at BESIII

Findings

Prospects