Abstract
The exclusive process , with and , has been studied at for measurement of the timelike electric and magnetic form factors, and . A data sample, corresponding to an integrated luminosity of , was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio and, for the first time for any baryon, the relative phase . The resulting values are and , respectively. These are obtained using the recently established and most precise value of the asymmetry parameter measured by BESIII. In addition, the cross section is measured with unprecedented precision to be , which corresponds to an effective form factor of . The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon timelike electromagnetic form factors.
- Received 25 March 2019
- Revised 26 June 2019
DOI:https://doi.org/10.1103/PhysRevLett.123.122003
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.
Published by the American Physical Society