<p> This dissertation shows the first evidence of the process <i>e</i><sup> +</sup><i>e</i><sup>−</sup> → γη<i><sub> c</sub></i>(1<i>S</i>) 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 <i>Y</i>(4260) and <i>Y</i>(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<sup>−1</sup>. We measure the Born cross section, σ<i><sub> E</sub></i>(<i>e</i><sup>+</sup><i>e</i><sup> −</sup> → γη<i><sub>c</sub></i>(1<i> S</i>)), at each energy using a combination of twelve η<i><sub> c</sub></i>(1<i>S</i>) decay channels. Because the significance of the signal is marginal at each energy (≤ 3.0σ), we also combine all six energies under various assumptions for the energy-dependence of the cross section. If a <i>Y</i>(4260) is assumed, we measure σ4<sub> .26</sub>(<i>e</i><sup>+</sup><i>e</i><sup>− </sup> → γη<i><sub>c</sub></i>(1<i>S</i>)) = 2.11 ± 0.49 (stat.) ± 0.33 (syst.) pb with a significance of 4.2σ. With our current statistics we are unable to distinguish the <i> Y</i>(4260) process from others.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:10143643 |
| Date | 01 October 2016 |
| Creators | Lara, Manuel |
| Publisher | Indiana University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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