Searching for neutral state in the rare decay $J/\psi \rightarrow e^+ e^- \phi$

TL;DR

This paper examines the decay $J/ar{ ext{psi}} ightarrow e^+ e^- ar{ ext{phi}}$ to search for neutral states like dark photons and dark Z, concluding that current constraints limit their observable effects in this process.

Contribution

It provides the first analysis of dark photon and dark Z effects in this specific decay channel, setting stringent constraints on their possible contributions.

Findings

Hadronic effects are negligible compared to electromagnetic contributions.

Constraints on dark photon and dark Z are very restrictive.

Observation of dark photon or dark Z in this decay is unlikely.

Abstract

We investigate the decay process $J/\psi \rightarrow e^+ e^-\phi$, where the relatively clean electromagnetic (EM) transitions dominate at leading order at the tree level, while hadronic contributions arise only through hadronic loop transitions. The branching ratio of $J/\psi \rightarrow e^+ e^-\phi$ was estimated to be approximately $2.28 \times 10^{-8}$ keV where the hadronic effects are negligible compared to the EM contributions. The upper limit on the branching fraction was set to be $B(J/\psi \rightarrow e^+ e^-\phi) < 1.2 \times 10^{-7}$ by BESIII collaboration. In this paper we investigate the existence of a neutral state such as dark photon and dark $Z$. Our analysis shows that the constraints on the dark photon and dark $Z$ are stringent in the way that large enhancement to the SM branching ratio up to the present experimental limit is not possible. Therefore, observing a signal for the dark photon and dark $Z$ in this decay channel is changeable.