Search for $C$ violation in the decay $\eta \to {\pi }^0+e^{+}+e^{-}$ with WASA-at-COSY

Abstract

We report on the investigation of the rare decay $\eta \to {\pi }^0+{\text{e}}^{+}+{\text{e}}^{-}$ which is of interest to study both $C$ violation in the electromagnetic interaction and to search for contributions from physics beyond the Standard Model, since the allowed decay via a two-photon intermediate state is strongly suppressed. The experiment has been performed using the WASA-at-COSY installation, located at the COSY accelerator of the Forschungszentrum Jülich, Germany. In total $3\times 10^7$ events of the reaction $\text{p}+\text{d}\to {}^3\text{He}+\eta$ have been recorded at an excess energy of $Q=59.8\text{MeV}$. Based on this data set the $C$ parity violating decay $\eta \to {\pi }^0+{\gamma }^{\ast }\to {\pi }^0+{\text{e}}^{+}+{\text{e}}^{-}$ via a single-photon intermediate state has been searched for, resulting in new upper limits of $\Gamma \left(\eta \to {\pi }^0+{\text{e}}^{+}+{\text{e}}^{-}\right)/\Gamma \left(\eta \to {\pi }^{+}+{\pi }^{-}+{\pi }^0\right)<3.28\times 10^{-5}$ and $\Gamma \left(\eta \to {\pi }^0+{\text{e}}^{+}+{\text{e}}^{-}\right)/\Gamma \left(\eta \to \text{all}\right)<7.5\times 10^{-6}(\text{CL}=90\%)$, respectively.

arXiv comment7 pages, 8 figures, submitted to PLB

References in corpus (6)

• The WASA Detector Facility at CELSIUS
• ABC Effect and Resonance Structure in the Double-Pionic Fusion to ${}^3$He
• Pluto: A Monte Carlo Simulation Tool for Hadronic Physics
• Measurements of Branching Ratios for $\eta$ Decays into Charged Particles
• Cross section ratio and angular distributions of the reaction p + d -> 3He + eta at 48.8 MeV and 59.8 MeV excess energy
• Tests of the fundamental symmetries in eta meson decays

Cited by in corpus (3)

• Precision tests of fundamental physics with $\eta$ and ${\eta }^{\prime }$ mesons
• Etaprime and Eta Mesons with Connection to Anomalous Glue
• The semileptonic decays ${\eta }^{(\prime )}\to {\pi }^0{\ell }^{+}{\ell }^{-}$ and ${\eta }^{\prime }\to \eta {\ell }^{+}{\ell }^{-}$ in the standard model