Search for production of a single top quark in association with a Z boson in Standard Model and New Physics scenarios using CMS Run 2 data.

Lead Research Organisation: Brunel University
Department Name: Electronic and Computer Engineering

Abstract

This project is to work on the analysis of the full Run 2 dataset collected by the CMS detector at the CERN-LHC. The data will be used to search for the production of a single top quark in association with a Z boson in the dilepton final state. This is a rare standard model (SM) process that has recently been observed for the first time, but only in the trilepton final state. In addition to shedding light on the process itself and how the top couples to Z bosons, it is also sensitive to the WWZ coupling.

Thus far, there has been no attempt to make the corresponding observation/measurement in the dilepton final state, which is more challenging from an analysis perspective, but also offers an important independent cross-check of the trilepton result and the potential to produce a more sensitive combined result. The full Run 2 dataset will be required for there to be any prospect of making an observation using this particular final state. The analysis will also be done using new CMS analysis techniques and tools, in contrast to the preceding work done in this area at Brunel.

In addition to looking for the SM process, the same (or at least a closely-related) subset of the Run 2 data can be used to search for flavour-changing neutral current (FCNC) tZ production. There are two separate decay processes that can be studied in this regard: One is the search for tZ production, where the FCNC vertex is part of the production mechanism, potentially shedding light on both tZq and tgq anomalous couplings. The other is the search for tZ production using events containing a top-quark pair, where the FCNC vertex occurs in the subsequent decay of one of the top quarks. This also has the potential to shed light on the tZq anomalous coupling.

Although the analyses described above will be the primary focus of this project, it is expected that there will also be work done on the maintenance and operation of the current CMS Tracker, participating in preparations for Run 3 data-taking.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
ST/S505286/1 01/10/2018 30/09/2022
2185053 Studentship ST/S505286/1 01/10/2018 30/09/2021 Kathryn Coldham