Limits on the production of the standard model Higgs boson in pp collisions at TeV with the ATLAS detector

Dipartimento di Fisica E. Fermi, Università di Pisa, Pisa, Italy
European Physical Journal C (Impact Factor: 5.08). 06/2011; 71(9):1-30. DOI: 10.1140/epjc/s10052-011-1728-9


A search for the Standard Model Higgs boson at the Large Hadron Collider (LHC) running at a centre-of-mass energy of 7TeV
is reported, based on a total integrated luminosity of up to 40pb−1 collected by the ATLAS detector in 2010. Several Higgs boson decay channels: H→γγ, H→ZZ
(∗)→ℓℓℓℓ, H→ZZ→ℓℓνν, H→ZZ→ℓℓqq, H→WW
(∗)→ℓνℓν and H→WW→ℓνqq (ℓis e, μ) are combined in a mass range from 110GeV to 600GeV. The highest sensitivity is achieved in the mass range between 160GeV
and 170GeV, where the expected 95% CL exclusion sensitivity is at Higgs boson production cross sections 2.3 times the Standard
Model prediction. Upper limits on the cross section for its production are determined. Models with a fourth generation of
heavy leptons and quarks with Standard Model-like couplings to the Higgs boson are also investigated and are excluded at 95%
CL for a Higgs boson mass in the range from 140 GeVto 185GeV.

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    • "The low SM Higgs mass region, [110] [140] GeV, is the most challenging for LHC searches. In this mass regime, the main search channel through the rare decay into a pair of photons can be complemented by the decay into τ + τ − and potentially the b ¯ b channel (particularly for the lower edge of the mass range and/or for supersymmetric Higgs searches), while the W W * , ZZ * channels are already competitive in the upper edge (130–140 GeV) of this mass range [1] the Higgs being produced mainly via gluon fusion [21], [22]. The theoretical predictions for the loop induced decays H → γγ (and H → γZ) have been initiated since many years [23] [24] [25]. "
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    ABSTRACT: We study the two photon decay channel of the Standard Model-like component of the CP-even Higgs bosons present in the type II Seesaw Model. The corresponding cross-section is found to be significantly enhanced in parts of the parameter space, due to the (doubly-)charged Higgs bosons' $(H^{\pm \pm})H^\pm$ virtual contributions, while all the other Higgs decay channels remain Standard Model(SM)-like. In other parts of the parameter space $H^{\pm \pm}$ (and $H^{\pm}$) interfere destructively, reducing the two photon branching ratio tremendously below the SM prediction. Such properties allow to account for any excess such as the one reported by ATLAS/CMS at $\approx 125$ GeV if confirmed by future data; if not, for the fact that a SM-like Higgs exclusion in the diphoton channel around 114-115 GeV as reported by ATLAS, does not contradict a SM-like Higgs at LEP(!), and at any rate, for the fact that ATLAS/CMS exclusion limits put stringent lower bounds on the $H^{\pm \pm}$ mass, particularly in the parameter space regions where the direct limits from same-sign leptonic decays of $H^{\pm \pm}$ do not apply.
    Journal of High Energy Physics 04/2012; 1204:136. DOI:10.1007/JHEP04(2012)136 · 6.11 Impact Factor

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    ABSTRACT: A search for a Higgs boson has been performed in the H â WW â âνjj channel in 1.04 fb⁻¹ of pp collision data at âs = 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No significant excess of events is observed over the expected background and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 240 GeV < m{sub H} < 600 GeV. The best sensitivity is reached for m{sub H} = 400 GeV, where the 95% confidence level upper bound on the cross section for H â WW production is 3.1 pb, or 2.7 times the standard model prediction.
    Physical Review Letters 01/2011; 107(23). DOI:10.1103/PhysRevLett.107.231801 · 7.51 Impact Factor
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