Statistical interpretation of exotics monojet data in search of an invisibly decaying Higgs Boson

Following the recent discovery of a Standard Model Higgs-like particle at the Large Hadron Collider, this study searches for the evidence of invisible decays of this particle. Assuming that this is the Standard Model Higgs boson, its decay to invisible particles is not expected to be measurable in the current data. However, it could have a large contribution from its decay to stable non-Standard Model particles such as the hypothetical dark matter particles. This study corresponds to 4.7 fb!1 of 7 TeV proton-proton collisions and 20.3 fb!1 of 8 TeV proton-proton collisions. At the time of thesis submission, the 8 TeV results were not unblinded by the ATLAS Collaboration, so toy-data are presented here to demonstrate the procedure. The performance of the statistical framework to be used in the combination of the 7 TeV data with the real 8 TeV data is assessed and is found to perform very well. The results are interpreted to set 95 confidence level limits on the branching ratio to invisible particles of the newly discovered Higgs-like particle at a mass of 125 GeV. Limits are also set on the production cross section ⇥ branching ratio of additional Higgs-like particles that decay invisibly in the mass range: 115 GeV to 300 GeV. In the combination of the 7 TeV data and 8 TeV toy-data, an expected (observed) upper limit of0.89 (0.59) is set on the branching ratio to invisible particles of a 125 GeV Higgs boson. In the mass range 115 to 300 GeV, no excess beyond the Standard Model expectation is observed.

Grantor dc:publisher.institution

Department of Physics

Year dc:date.issued

2014

Author dc:creator

• Mwewa, Chilufya

Advisor dc:contributor.advisor

• Hamilton, Andrew

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/9216

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/9216