Speaker
Description
We report on the latest searches for low mass states predicted in several New Physics models performed with the data collected by the BaBar detector at the PEP-II $e^+e^-$ collider.
In particular, we search for single-photon events in a sample corresponding to 53 fb$^{−1}$ of $e^+e^− $ collision data. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle $A’$ through the process $e^+e^- \to \gamma A’$, $A’ \to invisible$. Such particles, referred to as “dark photons”, are motivated by theories applying a $U(1)$ gauge symmetry to dark matter.
We find no evidence for such processes and set $90\%$ confidence level upper limits on the
coupling strength of $A’ \to e^+e^-$ for a dark photon with a mass lower than 8 GeV.?
In particular, our limits exclude the values of the $A’$ coupling suggested by the
dark-photon interpretation of the muon $(g-2)$ anomaly, as well as a broad range of parameters.
We also present a search for a new muonic dark force mediated by a
gauge boson ($Z’$) coupling only to the second and third lepton families.
The existence of the $Z’$ boson is probed in $e^+e^− \to \mu^+\mu^- Z’$, $Z’ \to \mu^+ \mu^-$ events,
No significant signal is observed. Limits on dark-sector coupling constants
are derived, improving the current constraints to the allowed parameter space.