Book/Dissertation / PhD Thesis

PUBDB-2015-03479

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Interference effects in new physics processes at the LHC

Fuchs, E. (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-2015-037

Report No.: DESY-THESIS-2015-037

Abstract: Interference effects between nearly mass-degenerate particles are ad-dressed in this thesis, comprising higher-order calculations, a model-independent method to calculate interference terms efficiently and aphenomenological application to current Higgs searches at the LHC.Predictions of cross sections and decay widths can be severelyaffected by interference terms between quasi-degenerate states arising inmodels beyond the Standard Model. We formulate a generalisation ofthe narrow-width approximation (NWA) which allows for a consistenttreatment of such effects by factorising the interference term into on-shellmatrix elements of the production and decay parts, optionally furtherapproximated as simple interference weight factors, incorporating one-loop and real corrections in a UV- and IR-finite way. We apply thegeneralised NWA to interfering MSSM Higgs bosons in the processχ 04 → χ 01 Φ → χ 01 τ + τ − , Φ = h, H and achieve an agreement of betterthan 1% with the unfactorised three-body decay of the neutralino χ 04at NLO. Further, we derive the approximation of the full propagatormatrix of the three neutral MSSM Higgs bosons in terms of Breit-Wigner propagators and on-shell wave-function normalisation factorsˆ This is found to accurately reproduce the full mixing properties alsoZ.in the case of complex MSSM parameters. Moreover, it enables theimplementation of the total width at the highest available order. Usingˆthe Breit-Wigner and Z-factorformalism, we calculate CP-violatinginterference effects of the neutral MSSM Higgs bosons in the processb ̄ b → h 1,2,3 → τ + τ − , induced by the phase φ A t . We find a very significant,destructive interference between h 2 and h 3 , particularly for large μ. Asa consequence, a considerable parameter region in the complex M h mod+scenario, which would appear to be ruled out if this interference wereneglected, actually escapes the current exclusion bounds from the LHC.

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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