Search for the Axion-Like-Particles in the $\eta \to {\pi }^{+}{\pi }^{-}{e}^{+}{e}^{-}$ decay with HADES detector

Abstract

The dark matter and existence of new particles are now a possible explanation of several physics phenomena which evade the predictions of the Standard Model. In this context Axion-Like-Particles (ALP) with masses in the MeV to GeV range with additional Peccei-Quinn breaking contribution, and which are coupled to the Standard Model have been postulated. To search for the existence of such new particles, we have launched dedicated analysis of a high statistics data sample collected by High-Acceptance Di-Electron Spectrometer (HADES) operating at GSI in Darmstadt. In particular, we study $\eta$ meson decays into ${\pi }^{+}{\pi }^{-}{e}^{+}{e}^{-}$, where hypothesized isoscalar gauge boson $a$ could be produced in the intermediate state $\eta \to {\pi }^{+}{\pi }^{-}a$ decaying predominantly to $e^{+}{e}^{-}$. In this report we describe the analysis strategy we applied to search for a resonant peak in the dilepton invariant mass spectrum $\eta \to {\pi }^{+}{\pi }^{-}a\to {\pi }^{+}{\pi }^{-}{e}^{+}{e}^{-}$ and present the method for event selection and particle identification.

8 pages, proceeding for the 21st International Conference on Hadron Spectroscopy and Structure (HADRON2025)