Measurement of the top quark mass in the dileptonic decay channel at CMS
This dissertation presents a measurement of the top quark mass (Mt) in the dileptonic decay channel using data from proton-proton collisions at √s = 8 TeV recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 19.7 ± 0.5 fb−1. The analysis is based on three observables whose distributions are sensitive to the value of Mt. The Mbl invariant mass and MT2 'stransverse mass' observables are employed in a simultaneous fit to determine the value of Mt and an overall jet energy scale factor (JSF). In a complementary approach, the MT2-assisted on-shell reconstruction technique is used to construct an Mblv invariant mass observable that is combined with MT2 to measure Mt. The shapes of the observables, along with their evolutions in Mt and JSF, are modeled by a non-parametric Gaussian process regression technique. The sensitivity of the observables to the value of Mt is investigated using a Fisher information density function. The top quark mass is measured to be 172.22 ± 0.18 (stat) ± 0.91 (syst) GeV. This dissertation also presents a missing transverse momentum (MET) significance variable, which is used to estimate the compatibility of the reconstructed MET with a zero nominal value. This variable may be used to discriminate between events containing real MET due to undetected particles and spurious MET due to object misreconstruction, finite detector resolution, or detector noise. The MET significance variable is tuned using data-driven techniques, and its performance is evaluated using the CMS Run 1 and Run 2 datasets.
Physics; CERN; high energy; large hadron collider; particle; standard model; top quark
Alexander, James Paul
Wittich, Peter; Perelstein, Maxim
PHD of Physics
Doctor of Philosophy
dissertation or thesis