Measurement of the phase between strong and electromagnetic amplitudes in the decay $J/\psi\to\phi\eta$

TL;DR

This study measures the phase difference between strong and electromagnetic decay amplitudes of the $J/$ particle into $\u03b7 ext{eta}$, using $e^+e^-$ collision data collected by BESIII, revealing a phase within a specific range.

Contribution

First direct measurement of the relative phase between strong and electromagnetic decay amplitudes in $J/$ decays to vector-pseudoscalar final states.

Findings

Relative phase between amplitudes is within [133°, 228°] at 68% confidence level.

Analysis used interference patterns in the cross section lineshape of $e^+e^- \u03b7 ext{eta}$.

Data collected at 26 energy points with 452 pb$^{-1}$ total luminosity.

Abstract

The first direct measurement of the relative phase between the strong and electromagnetic amplitudes for a $J/\psi$ decaying into a vector-pseudoscalar final state is performed using 26 energy points of $e^+e^-$ annihilation data between $3.00\ \text{GeV}$ and \mbox{3.12 GeV}. The data sets were collected by the BESIII detector with a total integrated luminosity of 452 pb$^{-1}$. By investigating the interference pattern in the cross section lineshape of $e^+e^-\to\phi\eta$, the relative phase between the strong and electromagnetic amplitudes of $J/\psi$ decay is determined to be within $[133^\circ,228^\circ]$ at 68\% confidence level.