The PADME experiment at LNF

TL;DR

PADME targets light dark photons in the MeV–GeV range by exploiting kinetic mixing and a missing-mass technique in $e^+e^- \to A'\gamma$ at a low-energy positron beam. The experiment employs a diamond active target, a spectrometer, a dipole magnet, vacuum, and a high-resolution calorimeter to measure the final-state kinematics and infer the missing mass $M_{miss}^2$, enabling searches for both invisible and visible $A'$ decays in the $M_{A'}$ window of a few to a few tens of MeV. A detailed GEANT4-based MC study accounts for backgrounds from bremsstrahlung and photon annihilation, showing that one-year running with realistic efficiency can reach $\epsilon^2 \sim 1\times10^{-6}$ for $2.5<M_{A'}<22.5$ MeV, with normalization via $e^+e^-\to\gamma\gamma$ and potential beam-dump extensions. The work demonstrates PADME’s role in complementing other searches for light dark sector particles and highlights the impact of possible DAΦNE linac upgrades on expanding the accessible mass range.

Abstract

Massive photon-like particles are predicted in many extensions of the Standard Model. They have interactions similar to the photon, are vector bosons, and can be produced together with photons. The PADME experiment proposes a search for the dark photon ($A'$) in the $e^+e^- \to γA'$ process in a positron-on-target experiment, exploiting the positron beam of the DA$Φ$NE linac at the Laboratori Nazionali di Frascati, INFN. In one year of running a sensitivity in the relative interaction strength down to $10^{-6}$ is achievable, in the mass region from 2.5 MeV $<M_{A'}<$ 22.5 MeV. The proposed experimental setup and the analysis technique is discussed.

Figures (7)

• Figure 1: Current exclusion limits and prospects for $A' \to e^+e^-$. Filled areas are excluded at 90% C.L. Lines represent regions accessible to future experiments. Adapted from Curtin:2014cca.
• Figure 2: Model independent bounds for $A' \to \chi\chi$Davoudiasl:2014kua.
• Figure 3: Schematic of the Positron Annihilation into Dark Matter Experiment (PADME).
• Figure 4: $M_{miss}^2$ for background events. In red with no selection cuts in blue after all cuts applied.
• Figure 5: Number of background events for different $A'$ mass hypothesis. In red $e^+e^-\to\gamma\gamma$ in blue total background after all cuts applied.