Phenomenology of the minimal <i>B - L</i> extension of the Standard Model at the LHC

A well-motivated framework to naturally introduce neutrino masses is the <i>B - L</i> model, a <i>U</i>(1) extension of the standard model related to the baryon minus lepton gauged number. Besides three right-handed neutrinos, that are included to cancel the anomalies (thereby naturally providing neutrino masses), this model also encompasses a complex scalar for the spontaneous symmetry breaking of the extended gauge sector and to give mass to the <i>Z'</i> boson. We present the phenomenology, the discovery potential at the LHC, and the most up-to-date experimental and theoretical limits of the new particles in this model. In the gauge sector, a <i>Z'</i> boson is present. We study its properties (i.e., production cross sections, branching ratios, total width), showing that it is dominantly coupled to leptons. We also present a detailed discovery power study at the LHC and at Tevatron for the <i>Z'</i> boson. In the fermion sector, after implementing the see-saw mechanism, we end up with three heavy neutrinos. We show that they can be long-lived particles (therefore providing displaced vertices in the detector), and that they can induce spectacular multi-lepton decays of the <i>Z'</i> boson. We also study the full signature <i>pp</i> → <i>Z'</i> → ν_hν_h, and present a parton level and a detector level analysis for the tri-lepton decay mode of the <i>Z'</i> boson via heavy neutrinos. In the gauge sector, the two Higgs fields mix. We derive the unitarity bound and the constraints from the renormalisation group equations study. In the allowed region of the parameter space, we delineate the phenomenology of the Higgs bosons and we show characteristic signatures of the latter, at the LHC, involving the <i>Z'</i> boson and the heavy neutrinos.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2011

Author dc:creator

• Basso, Lorenzo

Advisor dc:contributor.advisor

• Moretti, S.