Abstract
We study the electromagnetic Dalitz decay and search for dielectron decays of a dark gauge boson () in with the two decay modes and using events collected with the BESIII detector. The branching fraction of is measured to be , with a precision that is improved by a factor of 1.5 over the previous BESIII measurement. The corresponding dielectron invariant mass dependent modulus square of the transition form factor is explored for the first time, and the pole mass is determined to be . We find no evidence of production and set 90% confidence level upper limits on the product branching fraction as well as the kinetic mixing strength between the standard model photon and in the mass range of .
1 More- Received 8 October 2018
DOI:https://doi.org/10.1103/PhysRevD.99.012006
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