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The Higgs mechanism is responsible for the spontaneous breaking of the electroweak symmetry leading to the generation of masses of fermions and weak bosons. This thesis is devoted to search for the neutral supersymmetric Higgs particles Φ=h, H and A decaying into b quarks produced in association with at least one more b quark at the Large Hadron Collider. Here the study of the final states characterized by three b-tagged jets is described in detail. The analysis was performed using data corresponding to 2.7 − 4.8 fb^−1 integrated luminosity of pp collisions with a centre-of-mass energy of 7 TeV collected in 2011 with the CMS detector. Two analysis scenarios were adopted to perform a search for neutral Higgs bosons of low and medium masses, 90 GeV ≤ MΦ < 180 GeV and 180 ≤ GeV MΦ ≤ 350 GeV, respectively. Two-dimensional templates, built up from double-b-tagged data and based on the invariant mass of the two leading b jets and a variable reflecting b-jet properties of three leading jets, are used to model the background. The signal is modeled by templates obtained from Monte Carlo simulation. Various systematic effects affecting the signal efficiency and changing shapes of the signal and background templates were investigated.
The fitting machinery, based on a binned least-squares fit of the signal and background templates and the systematics model dependent on the hypothesized mass of the pseudoscalar Higgs particle A, was developed to extract the signal and background yields from the data. No significant evidence for the production of the Higgs bosons is found.
Using the CLS method, we set cross section times branching fraction upper limits at 95% confidence level (CL) on the production of such neutral Higgs bosons Φ in the mass range from 90 GeV to 350 GeV. The observed exclusion limits are well within the expected ±2σ band.
The benchmark scenario of the Minimal Supersymmetric Standard Model, denoted as mmax , with the two choices of the Higgsino mass parameter, μ = +200 GeV and μ = −200 GeV is considered. The obtained 95% CL upper limits on σ (pp → bb + Φ) × BR(Φ → bb) are interpreted as the upper limits on the MSSM parameter tan β . Ranges 27 ≤ tan β ≤ 51 and 22 ≤ tan β ≤ 37 for the masses of the Higgs boson from 90 to 350 GeV are ruled out at μ = +200 GeV and μ = −200 GeV, respectively. The 95% CL limits on tan β obtained in this channel supersede previous tan β limits established by CDF and D0 experiments.