L’IPHC | Thèses et stages Master » Les Doctorants de l’IPHC / The PhD Students of the IPHC » Pages pro » Anciens doctorants » MICONI Florian
Dernière mise à jour mardi 18 juin 2013, par
Institut Pluridisciplinaire Hubert Curien - IPHC
Département de Recherche Subatomique – DRS
Centre National de la Recherche Scientifique - CNRS
UMR 7178 CNRS/Université De Strasbourg - UDS
23 rue du loess, 67037 Strasbourg cedex 2, France
Contact : Florian MICONI
Titre de la thèse : Recherche d’un boson de Higgs standard de masse inférieure à 140 GeV/c2 avec l’expérience DØ au Tevatron.
Période : 2009-2012
Encadrant(s) : Isabelle RIPP-BAUDOT
The standard model of the particle physics is based on the notion of local gauge invariance. It is a very successful theory but it comes with a major flaw, even though local gauge invariance is a very elegant way to introduce interaction between fermions, it predicts a null mass for the corresponding bosons. And yet, mass of the electroweak bosons W+/- and Z has been measured non-null at CERN in 1983. Higgs boson has been introduce to explain these masses as an interaction with the Higgs field, but it’s still unobserved by any experiment.
Below 140 GeV/c2 the Higgs boson decays mainly in two b quarks. Finding this final state is very difficult in an hadronic environment because of the overwhelming amount of background containing b-jets. Thus the most sensitive channel is the production of a Higgs boson in association with a W boson. The decay of the W boson ( lepton + neutrino ) allow us to drastically reduce the hadronic background.
Higgs production being extremely rare, we have to develop sophisticated techniques to improve the signal sensitivity such as b-jet identification and multivariate analysis (mainly neural networks and boosted decision trees).
This work focused on :
And various studies on b-tagging (comparison of the b-tagging efficiency vs time and luminosity) and on the overall analysis (comparison of previous set of data vs new one, adding new reweighting and corresponding systematics uncertainties).
In the end, statistical approach allow us to set an upper limit on the ratio between the observed (resp. expected) Higgs production and its theoretical cross section. The results obtained in the WH channel with 5.3 fb-1 at Dø is 4.8 (resp. 4.5) for a 115 GeV/c2 Higgs boson.
Key words : Higgs, D0, Tevatron, multivariate analysis, neural network, decision tree, b-tagging.
Keywords : Particle physics, Higgs, D0, Tevatron, b-tagging, multivariate analysis, neural network, decision tree.