HPro: A NLO Monte-Carlo for Higgs production via gluon fusion with finite heavy quark masses

547

427

A 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 −1 at √ s = 7 TeV, and up to 5.3 fb −1 at √ s = 8 TeV. The results for five Higgs boson decay modes γγ, ZZ, WW, τ τ , 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, γγ and ZZ → 4 , 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. The CMS collaboration 106 Keywords: Hadron-Hadron Scattering IntroductionThe standard model (SM) [1-3] 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]. In the SM, the building blocks of matter, the fermions, are comprised of quarks and leptons. The interactions are mediated through the exchange of force carriers: the photon for electromagnetic interactions, the W and Z bosons for weak interactions, and the gluons for strong interactions. 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. It is realized by introducing a new complex scalar field into the model. By construction, this field allows the W and Z bosons to acquire mass whilst the photon remains massless, and adds to the model one new scalar particle, the SM Higgs boson (H). The Higgs scalar field and its conjugate can also give mass to the fermions, through Yukawa interactions [11][12][13] The discovery or exclusion of the SM Higgs boson is one of the primary scientific goals of the LHC. Previous direct searches at the LHC were based on data from protonproton collisions corresponding to an integrated luminosity of 5.1 fb −1 collected at a centreof-mass energy of 7 TeV. The CMS experiment excluded at 95% CL masses from 127 to 600 GeV [20]. The ATLAS experiment excluded at 95% CL the ranges 111. . Within the remaining allowed mass region, an excess of events between 2 and 3 standard deviations (σ) near 125 GeV was reported by both experiments. In 2012, the proton-proton centre-of-mass energy was increased to 8 TeV, and by the end of June, an...

Section: Signal Simulationmentioning

confidence: 99%

Observation of a new boson with mass near 125 GeV in pp collisions at $ \sqrt{s}=7 $ and 8 TeV

Chatrchyan¹,

Khachatryan²,

Sirunyan³

et al. 2013

547

427

“…2 We will include the soft-gluon resummation contributions in this indirect way since, as discussed in ref. [24], we would like to stick to the fixed order NNLO calculation for two main reasons: i) there are not yet parton distribution functions which include soft-gluon resummation and it appears inconsistent to fold a partonic cross section with PDFs that are not at the same order of perturbation theory (although the effects might be small in practice [42]) and ii) the soft-gluon resummation is not available for the Higgs+jet production cross sections and/or the Higgs cross sections including kinematical cuts (both are known only at NNLO [43][44][45][46][47]) which, ultimately, are the basic experimental inputs. level of a few percent; there are also small mixed NNLO QCD-electroweak effects which have been calculated [37] in an effective approach valid for M H ≪ M W .…”

Section: The Higgs Production Cross Sectionsmentioning

confidence: 99%

Higgs production at the lHC

Baglio

Djouadi

2011

172

194

Abstract:We analyze the production of Higgs particles at the early stage of the CERN large Hadron Collider with a 7 TeV center of mass energy (lHC). We first consider the case of the Standard Model Higgs boson that is mainly produced in the gluon-gluon fusion channel and to be detected in its decays into electroweak gauge bosons, gg → H → W W, ZZ, γγ. The production cross sections at √ s = 7 TeV and the decay branching ratios, including all relevant higher order QCD and electroweak corrections, are evaluated. An emphasis is put on the various theoretical uncertainties that affect the production rates: the significant uncertainties from scale variation and from the parametrization of the parton distribution functions as well as the uncertainties which arise due to the use of an effective field theory in the calculation of the next-to-next-to-leading order corrections. The parametric uncertainties stemming from the values of the strong coupling constant and the heavy quark masses in the Higgs decay branching ratios, which turn out to be non-negligible, are also discussed. The implications for different center of mass energies of the proton collider, √ s = 8-10 TeV as well as for the design energy √ s = 14 TeV, are briefly summarized. We then discuss the production of the neutral Higgs particles of the Minimal Supersymmetric extension of the Standard Model in the two main channels: gluon-gluon and bottom quark fusion leading to Higgs bosons which subsequently decay into tau lepton or b-quark pairs, gg, bb → Higgs → τ + τ − , bb. The Higgs production cross sections at the lHC and the decay branching ratios are analyzed. The associated theoretical uncertainties are found to be rather large and will have a significant impact on the parameter space of the model that can be probed.

“…The remaining part of the calculation is the same as in the SM [5][6][7]. Following the approach of [13], the NNLO corrections are normalized to the exact LO cross section according to Since bottom-quark effects are more important than in the SM, we compute them exactly through NLO [4,11]. We also include the full two-loop SM electroweak corrections of Ref.…”

Section: Precise Prediction Through Nnlomentioning

confidence: 99%

“…We apply our result to the composite Higgs model described above, where we introduce one or two multiplets of heavy top-partners. We include in our study the full bottom-mass dependence through NLO [4,11], the two-loop electroweak corrections [12] and the corresponding three-loop mixed QCD and electroweak corrections [13]. These effects are implemented in the program iHixs [14].…”

Section: Introductionmentioning

confidence: 99%

Gluon-fusion Higgs production at NNLO for a non-standard Higgs sector

Furlan¹

2011

Abstract:We consider an extension of the Standard Model with an arbitrary number of heavy quarks having general couplings to the Higgs boson. We construct an effective Lagrangian integrating out quarks that are heavier than half the mass of the Higgs boson and compute the Wilson coefficient for the effective gluon-Higgs vertex through NNLO. We apply our result to a composite Higgs model with vector-like quarks coupling to the third generation quarks. In the heavy quark-mass approximation, we show that the suppression of the leading-order cross section with respect to the Standard Model does not depend on the number of vector-like multiplets introduced. We analyse the effects of QCD and electroweak corrections through three loops, as well as bottom-quark contributions through two loops.