Book/Dissertation / PhD Thesis

PUBDB-2015-03458

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Boosted Searches For New Physics At The LHC

Schlaffer, M. (Corresponding author)DESY*

2015
Verlag Deutsches Elektronen-Synchrotron Hamburg

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Please use a persistent id in citations: doi:10.3204/DESY-THESIS-2015-036

Report No.: DESY-THESIS-2015-036

Abstract: During the first run of the LHC, no apparent signs of new physics beyond the StandardModel were discovered, but rather the Standard Model-like properties of the Higgs particleconfirmed. Therefore, new and powerful methods are needed to disclose the traces of newphysics, which is expected to be at the TeV scale in order to solve the hierarchy problem.In this thesis, we propose two complementary strategies for the quest for new physics atthe LHC. First, we show how a very boosted Higgs in association with a hard jet can beused to determine the important top Yukawa coupling in gluon fusion. In the inclusive gluonfusion process this is not feasible since possible deviations from its Standard Model value arecombined and can even cancel with the effective Higgs-gluon interaction mediated by newtop partners. This cancellation is motivated within minimal composite Higgs models butalso in certain regions of the MSSM parameter space and can lead to a Standard Model-likeinclusive cross section that allows no conclusions on the mass spectrum of the new physics.We work out in detail how this degeneracy can be broken in the boosted Higgs channel andfind that even in the worst case scenario with a Standard Model-like inclusive cross section,the top Yukawa coupling can be constrained to 0.8–1.3 times its Standard Model value at95% CL with an integrated luminosity of 3 000 fb −1 .The second strategy is targeted at direct stop and sbottom searches in the fully hadronictop decay channel. Since the stop, sbottom and neutralino masses are unknown, verydifferent event shapes are imaginable, ranging from unboosted top quarks and low missingenergy to highly boosted top quarks and large missing energy in the final state. In order tocover a wide range of possible event shapes and consequently stop, sbottom, and neutralinomasses, we combine several top taggers based on jet substructure techniques to obtain ascale invariant search strategy. The performance of this approach is shown in a colliderstudy where we find that stops with masses up to about 1 100 GeV can be excluded at 95%CL with an integrated luminosity of 100 fb −1 .

Note: Dissertation, Universität Hamburg, 2015

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Contributing Institute(s):

1. Theorie-Gruppe (T)

Research Program(s):

1. 611 - Fundamental Particles and Forces (POF3-611) (POF3-611)
2. PHGS, VH-GS-500 - PIER Helmholtz Graduate School (2015_IFV-VH-GS-500) (2015_IFV-VH-GS-500)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2015

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Database coverage:

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