Search for the CP-violating strong decays η → π + π ? and η ′(958)→π + π ?

摘要

A search for the CP -violating strong decays η → π + π ? and η ′ ( 958 ) → π + π ? has been performed using approximately 2.5 × 10 7 events of each of the decays D + → π + π + π ? and D s + → 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 ) + → π + η ( ′ ) with η ( ′ ) → π + π ? , and upper limits at 90% confidence level are set on the branching fractions, B ( η → π + π ? ) 1.6 × 10 ? 5 and B ( η ′ → π + π ? ) 1.8 × 10 ? 5 . The limit for the η decay is comparable with the existing one, while that for the η ′ is a factor of three smaller than the previous limit.