Observation of ψ (3686) →p p ̄ η′ and improved measurement of J /ψ →p p ̄ η′ OBSERVATION of ... M. ABLIKIM et al.

Abstract

We observe the process ψ(3686)→pp̄η′ for the first time, with a statistical significance higher than 10σ, and measure the branching fraction of J/ψ→pp̄η′ with an improved accuracy compared to earlier studies. The measurements are based on 4.48×108 ψ(3686) and 1.31×109 J/ψ events collected by the BESIII detector operating at the BEPCII. The branching fractions are determined to be B(ψ(3686)→pp̄η′)=(1.10±0.10±0.08)×10-5 and B(J/ψ→pp̄η′)=(1.26±0.02±0.07)×10-4, where the first uncertainties are statistical and the second ones systematic. Additionally, the η-η′ mixing angle is determined to be -24°±11° based on ψ(3686)→pp̄η′, and -24°±9° based on J/ψ→pp̄η′, respectively.