Search for the weak decay η′ →k±π and precise measurement of the branching fraction B (J /ψ →φη′) SEARCH for the WEAK DECAY ⋯ M. ABLIKIM et al.

We present the first search for the rare decay of η′ into K±π in J/ψ→φη′, using a sample of 1.3×109 J/ψ events collected with the BESIII detector. No significant signal is observed, and the upper limit at the 90% confidence level for the ratio B(η′→K±π)B(η′→γπ+π-) is determined to be 1.3×10-4. In addition, we report the measurement of the branching fraction of J/ψ→φη′ to be [5.10±0.03(stat)±0.32(syst)]×10-4, which agrees with previous results from BESII.