<p>Many Beyond-the-Standard-Model theories predict the existence of one or more additional neutral gauge bosons, or <i>Z'</i> bosons, with masses at the TeV scale or higher. A search for resonances of <i>Z'</i> bosons decaying to τ<sup>+</sup> τ<sup>-</sup> pairs in [special characters omitted]<i>s</i> = 8 TeV <i>pp</i> collisions from the LHC is presented. The data was collected by the ATLAS detector and corresponds to an integrated luminosity of 19.5-20.3 fb<sup>-1</sup>. The search is performed in ditau decay channels in which at least one tau decays hadronically. In each channel, the numbers of ditau events in high-mass regions of data are counted and compared to the expected numbers from Standard Model backgrounds and <i>Z'</i> signals. No statistically significant excess above the Standard Model expectation is observed in any channel. Bayesian 95% credibility upper limits are placed on the <i>Z'</i> production cross section times <i>Z'</i> → ττ branching ratio as functions of the <i>Z'</i> resonance mass for each channel and for a combination of the channels. Sequential Standard Model <i>Z'</i> bosons with masses below 2.02 TeV are excluded at 95% credibility. The impacts on the cross section limits from varying the <i>Z<sub>ssM</sub></i> decay width and couplings to fermions are evaluated. Limits are also placed on the cross section times branching ratio of Non-Universal <i>G</i>(221) <i> Z'</i> bosons with enhanced couplings to third-generation fermions. These are evaluated as functions of the <i>Z'<sub>NU</sub></i> mass and another free parameter. <i>Z'<sub>Nu</sub></i> bosons with masses below 1.3-2.1 TeV are excluded at 95% credibility.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:3663660 |
| Date | 08 August 2015 |
| Creators | Leister, Andrew Gerard |
| Publisher | Yale University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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