Infoscience

Thesis

# Search for exotic massive long-lived particles decaying semileptonically in the LHCb detector

Long-lived particles are predicted by numerous theories beyond the Standard Model. This thesis work is dedicated to the study of long-lived neutralinos decaying semileptonically into standard model particles. This decay channel is allowed by R-parity violation in the MSSM framework. A displaced vertex reconstructed with several tracks and an isolated high-$p_T$ muon is the expected typical signature. This search is motivated by the ability of the LHCb detector to reconstruct displaced vertices and by the low $p_T$ threshold of the muon trigger system that allow to study yet unexplored region of the theoretical parameter space. The analysis has been performed for neutralinos masses between $38$ and $198 GeV/c^2$ with a lifetime of $5$, $10$ and $50 ps$ on data collected from $pp$ collisions at center-of-mass energy of $\sqrt{s} = 7 TeV$ and $8 TeV$ during 2011 and 2012 at LHCb. The signal determination techniques has been validated with $Z$ and $W$ events with a topology similar to the signal. No evidence of these long-lived states has been observed, and upper limits on production cross-sections have been set.

Thèse École polytechnique fédérale de Lausanne EPFL, n° 6618 (2015)
Programme doctoral Physique
Faculté des sciences de base
Institut de physique de l'énergie et des particules
Laboratoire de physique des hautes énergies 1
Jury: Prof. V. Savona (président) ; Prof. A. Bay (directeur) ; Dr W. Hulsbergen, Dr P. Koppenburg, Prof. M. Q. Tran (rapporteurs)

Public defense: 2015-7-3

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Record created on 2015-06-23, modified on 2016-08-09