The so-called matrix-element method (MEM) has long been used successfully as a classificationtool in particle physics searches. In the presence of invisible final state particles, the traditionalMEM typically assigns probabilities to an event – based on whether it is more signal or background-like – through a phase space integration over all degrees of freedom of the invisible particles in theprocess(es). One inherent shortcoming of the traditional MEM is that the phase space integrationcan be slow, and therefore impractical for high multiplicity final states and/or large data sets. Therecent alternative of matrix-element maximisation has recently been introduced to circumvent thisproblem, since maximising a highly-dimensional function can be a far more CPU-efficient task thanthat of integration. In this work, matrix-element maximisation is applied to the process of fully-leptonic top associated Higgs production, where the Higgs boson decays to twob-quarks. A variety ofoptimisation algorithms are tested in terms of their performance and speed, and it is explicitly foundthat the maximisation technique is far more CPU-efficient than the traditional MEM at the cost of aslight reduction in performance. An interesting consequence of using matrix-element maximisationis that the result of the procedure gives an estimate of the four-momenta for the invisible particles inthe event. As a result, the idea of using these estimates as input information for more complicatedtools is discussed with potential prospects for future developments of the method.
Stefan von Buddenbrock
February, 2019 to May, 2020