Study of electromagnetic Dalitz decays χcJ →μ+μ-J /ψ

Abstract

Using 4.48×108 ψ(3686) events collected with the BESIII detector, we search for the decays χcJ→μ+μ-J/ψ through the radiative decays ψ(3686)→γχcJ, where J=0, 1, 2. The decays χc1,2→μ+μ-J/ψ are observed, and the corresponding branching fractions are measured to be B(χc1→μ+μ-J/ψ)=(2.51±0.18±0.20)×10-4 and B(χc2→μ+μ-J/ψ)=(2.33±0.18±0.29)×10-4, where the first uncertainty is statistical and the second one systematic. No significant χc0→μ+μ-J/ψ decay is observed, and the upper limit on the branching fraction is determined to be 2.0×10-5 at 90% confidence level. Also, we present a study of dimuon invariant mass dependent transition form factor for the decays χc1,2→μ+μ-J/ψ.