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Title: Jet substructure at the LHC with analytical methods
Author: Fregoso, Alessandro Virginio Armando
ISNI:       0000 0004 5355 0786
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2014
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Heavy boosted particles are being produced (or are expected, in the case of searches for new physics) in large quantities at the LHC. Unfortunately several search channels are normally not viable because of huge QCD backgrounds and non-perturbative contamination. Since the decay products of such particles tend to get clustered in the same jet however, it is possible to exploit the jet’s substructure to enhance signal significance. Many Monte Carlo studies of many different substructure techniques have been carried out so far, but little or no analytical insight into them is available. This work describes an original research aimed at filling this gap. As a first step towards a better understanding of jet substructure, we wish to investigate the solidity of common preferences of jet algorithms. Our benchmarks are jet rates. To start with, we use an approximate fixed-order approach in order to study the impact of different jet algorithms. The correctness of our results at the required accuracy is confirmed by checking against the program EVENT2. We then infer the resummation properties of these observables, allowing for a direct comparison of jet rates to the parton shower. Resummed results agree with Monte Carlo data from Herwig++. While carrying out this original work, a paper on a similar topic was published. Overlapping results are found to be in agreement. The important conclusion is that all inclusive algorithms (including anti-kT ) behave in the same way up to the considered accuracy. The next step is the study of substructure techniques, namely trimming, pruning and MDT. Again, we start with approximate fixed-order calculations. This provides enough information to write down resummed distributions, which clearly highlight the differences and similarities of the techniques under study. We propose several modifications to some of these, aimed to improve their performances; our final results are compared to Herwig++, and they turn out to be consistent with our predictions. A preliminary Monte Carlo study of signal efficiencies and significances completes this work, which constitutes an important first step towards an analytical understanding of the effects of substructure techniques on both signals and backgrounds.
Supervisor: Seymour, Michael; Dasgupta, Mrinal Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available