Observation of the electromagnetic doubly OZI-suppressed decay $J/\psi \rightarrow \phi \pi^{0}$

TL;DR

This paper reports the first evidence of the electromagnetic decay of J/psi into phi and pi0, observed using a large dataset, with interference effects influencing the measured branching fractions.

Contribution

First observation of the doubly OZI-suppressed electromagnetic decay J/psi to phi pi0 with detailed interference analysis.

Findings

Observation of the decay with two possible branching fractions.

Identification of interference effects in the K+K- mass spectrum.

Branching fractions measured as approximately 3×10^-6 and 1.2×10^-7.

Abstract

Using a sample of $1.31$ billion $J/\psi$ events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay $J/\psi \rightarrow \phi\pi^{0}$, which is the first evidence for a doubly Okubo-Zweig-Iizuka suppressed electromagnetic $J/\psi$ decay. A clear structure is observed in the $K^{+} K^{-}$ mass spectrum around 1.02 GeV/$c^2$, which can be attributed to interference between $J/\psi \rightarrow \phi\pi^{0}$ and $J/\psi \rightarrow K^{+}K^{-}\pi^{0}$ decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of $J/\psi \to \phi\pi^{0}$ are $[2.94 \pm 0.16\text{(stat.)} \pm 0.16\text{(syst.)}] \times 10^{-6}$ and $[1.24 \pm 0.33\text{(stat.)} \pm 0.30\text{(syst.)}] \times 10^{-7}$.