Search for CP and $P$ violating pseudoscalar decays into $\pi\pi$

TL;DR

This study searches for CP and P violating decays of eta, eta', and eta_c into pion pairs using a large J/psi sample, setting upper limits on their branching ratios due to no observed signals.

Contribution

First search for CP and P violating pseudoscalar decays into pion pairs in J/psi radiative decays, establishing new upper limits on their branching ratios.

Findings

No significant signals observed for the decays.

Set 90% confidence level upper limits on branching ratios.

Improved constraints on CP and P violation in pseudoscalar decays.

Abstract

Using a sample of $(225.2\pm 2.8)\times 10^6$ $J/\psi$ events collected with the Beijing Spectrometer (BESIII) at the Beijing Electron-Positron Collider, CP and $P$ violating decays of $\eta$, $\eta'$ and $\etac$ into $\pi^+\pi^-$ and $\pi^0 \pi^0$ are searched for in $\jpsi$ radiative decays. No significant $\eta$, $\eta'$ or $\etac$ signal is observed, and 90% confidence level upper limits of $\BR(\eta \to \pi^+\pi^-)<3.9\times 10^{-4}$, $\BR(\eta' \to \pi^+\pi^-)<5.5\times 10^{-5}$, $\BR(\etac \to \pi^+\pi^-)<1.3\times 10^{-4}$, $\BR(\eta \to \pi^0 \pi^0)<6.9\times 10^{-4}$, $\BR(\eta' \to \pi^0 \pi^0)<4.5\times 10^{-4}$ and $\BR(\etac \to \pi^0 \pi^0)<4.2\times 10^{-5}$ are obtained.