Evidence for e+e - to gammaetac(1S) at center-of-mass energies between 4.01 and 4.60 GeV at BESIII

摘要

This dissertation shows the first evidence of the process e +e- → gammaeta c(1S) using data collected by the BESIII experiment operating at BEPCII. This process can be used as a probe to study the nature of recently discovered charmonium-like Y states between 4.0 and 4.6 GeV, including the Y(4260) and Y(4360). Data collected at six center-of-mass energies are analyzed, namely: 4.01, 4.23, 4.26, 4.36, 4.42, and 4.60 GeV, corresponding to a total integrated luminosity of 4.6 fb-1. We measure the Born cross section, sigma E(e+e - → gammaetac(1 S)), at each energy using a combination of twelve eta c(1S) decay channels. Because the significance of the signal is marginal at each energy (≤ 3.0sigma), we also combine all six energies under various assumptions for the energy-dependence of the cross section. If a Y(4260) is assumed, we measure sigma4 .26(e+e- → gammaetac(1S)) = 2.11 +/- 0.49 (stat.) +/- 0.33 (syst.) pb with a significance of 4.2sigma. With our current statistics we are unable to distinguish the Y(4260) process from others.