Search for a dark vector gauge boson decaying to $\pi^+ \pi^-$ using $\eta \rightarrow \pi^+\pi^- \gamma$ decays

TL;DR

This paper searches for a hypothetical dark vector gauge boson decaying into pion pairs within specific meson decay chains, setting limits on its coupling strength in the 290-520 MeV/c^2 mass range using Belle data.

Contribution

First search for a dark vector gauge boson in meson decays with limits set on its coupling in the specified mass range.

Findings

No signal observed for the dark gauge boson.

Set mass-dependent limits on the baryonic fine structure constant.

Analyzed 976 fb$^{-1}$ of Belle data.

Abstract

We report a search for a dark vector gauge boson $U^\prime$ that couples to quarks in the decay chain $D^{*+} \to D^0 \pi^+, D^0 \to K^0_S \eta, \eta \to U^\prime \gamma$, $U^\prime \to \pi^+ \pi^-$. No signal is found and we set a mass-dependent limit on the baryonic fine structure constant of $10^{-3} - 10^{-2}$ in the $U^\prime$ mass range of 290 to 520 MeV/$c^2$. This analysis is based on a data sample of 976 fb$^{-1}$ collected by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider.