Search for the $C\!P$-violating strong decays $η\to π^+π^-$ and $η^\prime(958) \to π^+π^-$

Abstract

A search for the $C\!P$-violating strong decays $η\to π^+π^-$ and $η^\prime(958) \to π^+π^-$ has been performed using approximately $2.5 \times 10^{7}$ events of each of the decays $D^+ \to π^+π^+π^-$ and $D_s^+ \to π^+π^+π^-$, recorded by the LHCb experiment. The data set corresponds to an integrated luminosity of 3.0 fb$^{-1}$ of $pp$ collision data recorded during LHC Run 1 and 0.3 fb$^{-1}$ recorded in Run 2. No evidence is seen for $D^+_{(s)} \to π^+ η^{(\prime)}$ with $η^{(\prime)} \to π^+π^-$, and upper limits at 90% confidence level are set on the branching fractions, $\mathcal{B}(η\to π^+π^-) < 1.6 \times 10^{-5}$ and $\mathcal{B}(η^\prime \to π^+π^-) < 1.8 \times 10^{-5}$. The limit for the $η$ decay is comparable with the existing one, while that for the $η^\prime$ is a factor of three smaller than the previous limit.

All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-046.html