Ph.D. Thesis Title:

"Measurement of the Top Quark Mass in the All-Hadronic Top-Antitop Decay Channel Using Proton-Proton Collision Data from the ATLAS Experiment at a Centre-of-Mass Energy of 8 TeV"

The thesis component of my Ph.D. program focused on making a precision measurement of the top quark mass using the complete 2012 ATLAS dataset.  The energy per proton for the 2012 data-taking period was 4 TeV.  Working at such a high centre-of-mass energy (√s = 8 TeV), with many hard-scatter interactions greatly exceeding the threshold for top quark production, allowed for a substantial number of reconstructed candidate top quarks in our final dataset, even following our very tight set of event selection cuts employed to identify signal events.  In analyzing the proton-proton collision data, we searched specifically for pairs of top quarks (top/antitop quark pairs) which decayed to an all-hadronic or all-jet final state.

The analysis itself reflects a joint effort on behalf of the entire ATLAS collaboration.  The primary analyzers were from Carleton University in Ottawa (myself and F.G.Oakham), and several members of the ATLAS HEC group from the Max-Planck-Institut für Physik in Munich.

Work is presently ongoing to have the finalized ATLAS result published in a refereed physics journal.


Ph.D. Thesis Abstract:


PDF Version of the thesis:

The actual thesis can be found here.  Careful, it's a rather large (16.4 MB) file.  The (nicer looking) singled-spaced version of my thesis is also available for download from the CERN Document Server. 

The link to the entry can be found here: CERN-THESIS-2015-275

The corresponding publication from the ATLAS Collaboration appears in the Journal of High Energy Physics (JHEP) and is available at the following links: Inspire / Springer

 

Evolution of final data distribution

The key distribution from this top-quark mass measurement is a one-dimensional histogram of a quantity referred to as R32.  It corresponds to the ratio of the reconstructed invariant mass of each top quark candidate divided by the invariant mass of its associated reconstructed W boson.  Since the mass of the W boson is roughly 80 GeV and that of the top quark is close to 173 GeV, one could expect a peak arising from signal events at values of R32 close to 2.15.  And this is in fact what is observed.  There are many detector-level effects mixed in there which I don't discuss here, so take those numbers with a grain of salt.  The point is that a signal peak should start to emerge over the background as you add more and more data events.  This observable (R32) is used to probe the mass of the top quark using a so-called template method.


Carleton University has a strong ATLAS group consisting of four faculty members, as well as engineers, technicians, IT support staff, several M.Sc., Ph.D. students and the occasional summer or 4th-year undergraduate student.  For more information on their latest work check out the Carleton ATLAS Group's page.

I was fortunate to work under the guidance of Professor Gerald Oakham throughout my time as a graduate student at Carleton.


Acknowledgements

I'd like to acknowledge the generous financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC) over the course of my M.Sc. and Ph.D. programs at Carleton University.