Searching for the Dark Photon with PADME

Abstract

The PADME Experiment at Laboratori Nationali di Frascati is designed to search for the Dark Photon, a hypothetical gauge boson responsible for the interaction between the visible and the hidden sector. PADME explores the process of annihilation of beam positrons with the electrons in a fixed target, employing the missing mass technique: in case the annihilation results in the associate production of one visible and one Dark photon, the first can be registered by the experiment's electromagnetic calorimeter and the Dark Photon mass can be reconstructed knowing the beam energy. This paper presents the analysis techniques that are being employed for the PADME data, as well as the background composition and rejection procedure.

Figures (3)

• Figure 1: PADME Run II setup with several different particles and processes, observed in the experiment. Photons are shown in green, positrons in red and the hypothetical Dark Photon in blue. The continiuous arrows represent two photons, originating from an $e^+e^-\rightarrow\gamma\gamma$ annihilation event; the dashed lines - a photon and a Dark Photon, produced in an $e^+e^-\rightarrow\gamma A'$ event and the dotted lines - a positron and a photon, coming from a Bremsstrahlung event.
• Figure 2: Squared missing mass for photons in simulated $e^+e^-\rightarrow\gamma A'$ events where a single 430 MeV positron hits the target. The $\sigma_{M_{miss}^2}$ decreases with $M_{A'}$ approaching 22 MeV.
• Figure 3: Photon energy in the SAC versus the positron position in the PVeto for in-time $\gamma~e^+$ pairs obtained for MC simulation with $E_{beam}$ = 432 MeV and $2.5\times 10^4$ positrons per bunch.