Bringing the Higgs Boson to Rest

Date created: 
Standard Model
Particle physics
ATLAS detector
Higgs boson
Multivariate analysis
Boosted regression trees

Within the Standard Model of particle physics, the Higgs boson can decay to a pair of W bosons which decay leptonically. Despite its relatively large branching ratio, this is a challenging channel in which to search for the Higgs boson since we cannot detect neutrinos directly with the ATLAS detector. The matrix element method is a first principles approach that allows for better separation of signal and background by responding to subtle differences in the measured event kinematics. A straightforward implementation of the method is to assume that the Higgs boson is produced at rest in the transverse plane. However, this is often not the case due to next-to-leading order effects like initial state radiation. In order to improve the sensitivity of the matrix element analysis, we developed an estimator for the transverse momentum of the Higgs boson that allows us to boost it into its transverse rest frame. Using a regression tree algorithm to estimate the transverse kinematics of the Higgs boson on an event-by-event basis, we observe a 15% improvement in sensitivity. The application of this technique to Higgs boson property measurements, such as the determination of its spin, is also explored.

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Senior supervisor: 
Bernd Stelzer
Science: Department of Physics
Thesis type: 
(Thesis) M.Sc.