Evidence for e~+ e~- → γη_c(1S) at center-of-mass energies between 4.01 and 4.60 GeV

摘要

We present first evidence for the process e~+e~-→ γη_c(1S) at six center-of-mass energies between 4.01 and 4.60 GeV using data collected by the BESⅢ experiment operating at BEPCⅡ. We measure the Born cross section at each energy using a combination of twelve η_c (1S) decay channels. We also combine all six energies under various assumptions for the energy-dependence of the cross section. If the process is assumed to proceed via the Y(4260), we measure a peak Born cross section σ_(peak)(e~+e~-→ γn_c(1S)) = 2.11 ±0.49(stat.) ±0.36(syst.) pb with a statistical significance of 4.2σ.