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

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 $\eta$, ${\eta }^{\prime }$ and $\etac$ into ${\pi }^{+}{\pi }^{-}$ and ${\pi }^0{\pi }^0$ are searched for in $\jpsi$ radiative decays. No significant $\eta$, ${\eta }^{\prime }$ or $\etac$ signal is observed, and 90% confidence level upper limits of $\BR(η\to π^+π^-)<3.9\times 10^{-4}$, $\BR(η' \to π^+π^-)<5.5\times 10^{-5}$, $\BR(\etac \to π^+π^-)<1.3\times 10^{-4}$, $\BR(η\to π^0 π^0)<6.9\times 10^{-4}$, $\BR(η' \to π^0 π^0)<4.5\times 10^{-4}$ and $\BR(\etac \to π^0 π^0)<4.2\times 10^{-5}$ are obtained.

15 pages, 6 figures