Abstract
Using a data set of 2.93 fb−1 taken at a center-of-mass energy s=3.773 GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, also denoted as a dark photon. We examine the initial state radiation reactions e+e−→e+e−γISR and e+e−→μ+μ−γISR for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs. We observe no obvious enhancement in the mass range between 1.5 and 3.4 GeV/c2 and set a 90% confidence level upper limit on the mixing strength of the dark photon and the Standard Model photon. We obtain a competitive limit in the tested mass range.
Highlights
GSI Helmholtzcentre for Heavy Ion Research GmbH, D-64291 Darmstadt, Germany Guangxi Normal University, Guilin 541004, People’s Republic of China GuangXi University, Nanning 530004, People’s Republic of China
We examine the initial state radiation reactions e+e− → e+e−γISR and e+e− → μ+μ−γISR for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs
The ratio of the measured energy in the Electro-Magnetic Calorimeter (EMC), E, to the momentum p obtained from the Multilayer Drift Chamber (MDC) is used
Summary
GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, denoted as a dark photon. The ratio of the measured energy in the EMC, E, to the momentum p obtained from the MDC is used Both charged tracks must satisfy E/p > 0.8 c. We apply stronger requirements for the e+e−γISR final state, to provide a better suppression of the non-ISR background which is higher in the e+e− channel compared to the μ+μ− channel. In this case, χ21C < 5, and θγ < 0.05 radians, or θγ > π − 0.05 radians. In order to search for narrow structures on top of the QED background, 4th order polynomial functions to describe the continuum
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