Observation of e~+ e~- → γχ_(c1) and search for e~+ e~- → γχ_(c0), γχ_(c2), and γη_c at √s near 10.6 GeV at Belle

摘要

Using data samples of 89.5 fb~(-1), 711.0 fb~(-1), and 121.4 fb~(-1) collected with the Belle detector at the KEKB asymmetric-energy e+e- collider at center-of-mass energies 10.52, 10.58, and 10.867 GeV, respectively, we study the exclusive reactions e~+e~- → γχ_(cJ) (J = 0, 1, 2) and e~+e~- → γη_c. A significant γχ_(c1) signal is observed for the first time at √s= 10.58 GeV with a significance of 5.1σ including systematic uncertainties. No significant excesses for γχ_(c0), γχ_(c2), and γηc final states are found, and we set 90% credibility level upper limits on the Born cross sections (σ_B) at 10.52 GeV, 10.58 GeV, and 10.867 GeV. Together with cross sections measured by BESIII at lower center-of-mass energies, the energy dependency of σ_B(e~+e~- → γχ_(c1)) is obtained.