Simon Fraser University

Doug Schouten wins Quirks and Quarks Graduate Award for Best PhD Thesis of the year

Aug 3, 2012

Congratulations to Doug Schouten, whose thesis, Determination of the QCD Jet Energy Scale and Measurement of the Single Top Quark Cross Section at ATLAS, has earned the Quirks and Quarks Graduate Award for Best PhD Thesis of the year. Here's how Doug summarizes his work:

My research was performed using the ATLAS detector at the Large Hadron Collider (LHC) at the Centre for European Nuclear Research (CERN). Using the ATLAS detector, I studied the production of heavy "top" quarks, as they were created in the very high energy proton~proton collisions generated by the LHC.

Top quarks are one of six types of quarks, which are the fundamental building blocks of all observed matter. Because the top quark is so massive, measurements involving it play key roles in constraining theoretical models in physics, such as the Higgs mechanism. In my thesis, I measured the rate at which top quarks are produced via the weak nuclear force. This is especially difficult because this has a much lower rate than for top quark events produced via the strong nuclear force, and because the final decay products are very similar to background processes that occur with very high rates. However, it also adds unique information, since the fundamental interactions taking place are different.

The lifetime of top quarks is very small, on the order of 10^-24 seconds. Typically, they decay very quickly to a particle known as a W boson, and a bottom quark (which then produces a jet), in association with a so-called spectator jet. Since jets are one of the decay products in the events in which a top quark is produced, a calibration developed in my thesis was an important input into the top quark measurement. My research focused on using the data collected at ATLAS to first determine the rates of the background processes with very good accuracy, so that 
by subtracting the estimated backgrounds from the total sample of events, we could infer the rate of the single top quark production. This was the first such measurement performed at the LHC, and served as a benchmark measurement upon which future analysis could be built.