Abstract
AbstractA detailed description is reported of the analysis used by the CMS Collaboration in the search for the standard model Higgs boson in pp collisions at the LHC, which led to the observation of a new boson. The data sample corresponds to integrated luminosities up to 5.1 fb−1at$ \sqrt{s}=7 $TeV, and up to 5.3 fb−1at$ \sqrt{s}=8 $TeV.The results for five Higgs boson decay modesγγ, ZZ, WW,ττ, and bb, which show a combined local significance of 5 standard deviations near 125 GeV, are reviewed. A fit to the invariant mass of the two high resolution channels,γγand ZZ → 4ℓ, gives a mass estimate of 125.3 ± 0.4 (stat.) ± 0.5 (syst.) GeV. The measurements are interpreted in the context of the standard model Lagrangian for the scalar Higgs field interacting with fermions and vector bosons. The measured values of the corresponding couplings are compared to the standard model predictions. The hypothesis of custodial symmetry is tested through the measurement of the ratio of the couplings to the W and Z bosons. All the results are consistent, within their uncertainties, with the expectations for a standard model Higgs boson.
Highlights
The standard model (SM) [1,2,3] of particle physics accurately describes many experimental results that probe elementary particles and their interactions up to an energy scale of a few hundred GeV [4]
Events at the generator level are reweighted according to the total cross section σ(pp → H), which contains contributions from gluon-gluon fusion up to next-to-next-to-leading order (NNLO) and next-to-next-toleading-log (NNLL) terms [25, 59,60,61,62,63,64,65,66,67,68,69,70,71,72,73], vector-boson fusion including NNLO quantum chromodynamic (QCD) and NLO electroweak (EW) terms [25, 74,75,76,77,78], associated production VH at NNLO QCD and NLO EW [79,80,81,82,83,84], and the production in association with tt at NLO QCD [85,86,87,88]
The background contribution from ZZ production via qq is generated at NLO with powheg, while other diboson processes (WW, WZ) are generated with MadGraph [104, 105] with cross sections rescaled to NLO predictions
Summary
The standard model (SM) [1,2,3] of particle physics accurately describes many experimental results that probe elementary particles and their interactions up to an energy scale of a few hundred GeV [4]. All the elementary particles acquire mass through their interaction with the Higgs field [5,6,7,8,9,10,11,12,13] This mechanism, called the “Higgs” or “BEH” mechanism [5,6,7,8,9,10], is the first coherent and the simplest solution for giving mass to W and Z bosons, while still preserving the symmetry of the Lagrangian. In the summer 2012 the analysis of the full data set by the CDF and D0 Collaborations resulted in an excess of events of about 3σ in the mass range 120 ≤ mH ≤ 135 GeV, while searching for a SM Higgs boson decaying into b quarks [24]. The measured values can shed light on the nature of the newly observed particle because the Higgs boson couplings to fermions are qualitatively different from those to bosons. The results are combined and the first measurements of the couplings of the new particle to bosons and fermions are presented
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