Study of electromagnetic Dalitz decays chi(cJ )-> mu(+)mu(-) J/psi

Abstract

Using 4.48 x 10(8) psi(3686) events collected with the BESIII detector, we search for the decays chi(cJ) ->mu(+)mu(- )J/psi through the radiative decays psi(3686) -> gamma chi(cJ), where J = 0, 1, 2. The decays chi(c1,2) -> mu(+)mu(-)J/psi are observed, and the corresponding branching fractions arc measured to be B(chi(c1) -> mu(+)mu(-) J/psi) = (2.51 +/- 0.18 +/- 0.20) x 10(-4) and B(chi(c2 )-> mu(+)mu(- )J/psi) = (2.33 +/- 0.18 +/- 0.29) x 10(-4), where the first uncertainty is statistical and the second one systematic. No significant chi(c0 )-> mu(+)mu(- )J/psi decay is observed, and the upper limit on the branching fraction is determined to be 2.0 x 10(-5) at 90% confidence level. Also, we present a study of dimuon invariant mass dependent transition form factor for the decays chi(c1,2 )->mu(+)mu(- )J/psi.