Determination of spin and parity of the Higgs boson in the WW∗→eνμν decay channel with the ATLAS detector

Studies of the spin and parity quantum numbers of the Higgs boson in the WW∗→eνμν final state are presented, based on proton--proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb−1 at a centre-of-mass energy of s√=8 TeV. The Standard Model spin-parity JCP=0++ hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even (JCP=0++) or CP-odd (JCP=0+−) Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.

Constraints on new phenomena via Higgs boson couplings and invisible decays with the ATLAS detector

The ATLAS experiment at the LHC has measured the Higgs boson couplings and mass, and searched for invisible Higgs boson decays, using multiple production and decay channels with up to 4.7 fb−1 of pp collision data at √s=7 TeV and 20.3 fb−1 at √s=8 TeV. In the current study, the measured production and decay rates of the observed Higgs boson in the γγ, ZZ, W W , Zγ, bb, τ τ , and μμ decay channels, along with results from the associated production of a Higgs boson with a top-quark pair, are used to probe the scaling of the couplings with mass. Limits are set on parameters in extensions of the Standard Model including a composite Higgs boson, an additional electroweak singlet, and two-Higgs-doublet models. Together with the measured mass of the scalar Higgs boson in the γγ and ZZ decay modes, a lower limit is set on the pseudoscalar Higgs boson mass of m A > 370 GeV in the “hMSSM” simplified Minimal Supersymmetric Standard Model. Results from direct searches for heavy Higgs bosons are also interpreted in the hMSSM. Direct searches for invisible Higgs boson decays in the vector-boson fusion and associated production of a Higgs boson with W/Z (Z → ℓℓ, W/Z → jj) modes are statistically combined to set an upper limit on the Higgs boson invisible branching ratio of 0.25. The use of the measured visible decay rates in a more general coupling fit improves the upper limit to 0.23, constraining a Higgs portal model of dark matter.

Study of (W/Z)H production and Higgs boson couplings using H -> WW* decays with the ATLAS detector

A search for Higgs boson production in association with a W or Z boson, in the H→ W W ∗ decay channel, is performed with a data sample collected with the ATLAS detector at the LHC in proton-proton collisions at centre-of-mass energies s√=7 TeV and 8 TeV, corresponding to integrated luminosities of 4.5 fb−1 and 20.3 fb−1, respectively. The WH production mode is studied in two-lepton and three-lepton final states, while two- lepton and four-lepton final states are used to search for the ZH production mode. The observed significance, for the combined W H and ZH production, is 2.5 standard deviations while a significance of 0.9 standard deviations is expected in the Standard Model Higgs boson hypothesis. The ratio of the combined W H and ZH signal yield to the Standard Model expectation, μ V H , is found to be μ V H  = 3.0 − 1.1 + 1.3 (stat.) − 0.7 + 1.0 (sys.) for the Higgs boson mass of 125.36 GeV. The W H and ZH production modes are also combined with the gluon fusion and vector boson fusion production modes studied in the H → W W ∗ → ℓνℓν decay channel, resulting in an overall observed significance of 6.5 standard deviations and μ ggF + VBF + VH = 1. 16 − 0.15 + 0.16 (stat.) − 0.15 + 0.18 (sys.). The results are interpreted in terms of scaling factors of the Higgs boson couplings to vector bosons (κ V ) and fermions (κ F ); the combined results are: |κ V | = 1.06 − 0.10 + 0.10 , |κ F | = 0. 85 − 0.20 + 0.26 .

Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector

A search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb−1 of proton-proton collision data recorded by the ATLAS experiment at s√=8 TeV at the Large Hadron Collider. Five final states, targeting the decays H→WW∗, ττ, and ZZ∗, are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons (e or μ) without a hadronically decaying τ lepton; three light leptons; two same-charge light leptons with a hadronically decaying τ lepton; four light leptons; and one light lepton and two hadronically decaying τ leptons. No significant excess of events is observed above the background expectation. The best fit for the tt¯H production cross section, assuming a Higgs boson mass of 125 GeV, is 2.1+1.4−1.2 times the SM expectation, and the observed (expected) upper limit at the 95% confidence level is 4.7 (2.4) times the SM rate. The p-value for compatibility with the background-only hypothesis is 1.8σ; the expectation in the presence of a Standard Model signal is 0.9σ.

Study of the spin and parity of the Higgs boson in diboson decays with the ATLAS detector

Studies of the spin, parity and tensor couplings of the Higgs boson in the H→ZZ∗→4ℓ , H→WW∗→eνμν and H→γγ decay processes at the LHC are presented. The investigations are based on 25 fb−1 of pp collision data collected by the ATLAS experiment at s√=7 TeV and s√=8 TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers JP=0+, is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9% confidence level. Using the H→ZZ∗→4ℓ and H→WW∗→eνμν decays, the tensor structure of the HVV interaction in the spin-0 hypothesis is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplings are compatible with the SM predictions and constraints on the non-SM couplings are derived.

Search for a new resonance decaying to a W or Z boson and a Higgs boson in the ℓℓ/ℓν/νν+bb¯final states with the ATLAS detector

A search for a new resonance decaying to a W or Z boson and a Higgs boson in the ℓℓ/ℓν/νν+bb¯ final states is performed using 20.3 fb−1 of pp collision data recorded at s√= 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH/ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.

Searches for Higgs boson pair production in the hh→bbττ,γγWW∗,γγbb,bbbb channels with the ATLAS detector

Searches for both resonant and non-resonant Higgs boson pair production are performed in the hh→bbττ,γγWW∗ final states using 20.3 fb−1 of pp collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the Large Hadron Collider. No evidence of their production is observed and 95% confidence level upper limits on the production cross sections are set. These results are then combined with the published results of the hh→γγbb,bbbb analyses. An upper limit of 0.69 (0.47) pb on the non-resonant Standard Model like hh production is observed (expected), corresponding to 70 (48) times of the SM gg→hh cross section. For production via narrow resonances, cross section limits of hh production from a heavy Higgs boson decay are set as a function of the heavy Higgs boson mass. The observed (expected) limits range from 2.1 (1.1) pb at 260 GeV to 0.011 (0.018) pb at 1000 GeV. These results are interpreted in the context of two simplified scenarios of the Minimal Supersymmetric Standard Model.

Search for new light gauge bosons in Higgs boson decays to four-lepton final states in pp collisions at s√=8TeV with the ATLAS detector at the LHC

This paper presents a search for Higgs bosons decaying to four leptons, either electrons or muons, via one or two light exotic gauge bosons Zd, H→ZZd→4ℓ or H→ZdZd→4ℓ. The search was performed using pp collision data corresponding to an integrated luminosity of about 20 fb−1 at the center-of-mass energy of s√=8TeV recorded with the ATLAS detector at the Large Hadron Collider. The observed data are well described by the Standard Model prediction. Upper bounds on the branching ratio of H→ZZd→4ℓ and on the kinetic mixing parameter between the Zd and the Standard Model hypercharge gauge boson are set in the range (1--9)×10−5 and (4--17)×10−2 respectively, at 95% confidence level assuming the Standard Model branching ratio of H→ZZ∗→4ℓ, for Zd masses between 15 and 55 GeV. Upper bounds on the effective mass mixing parameter between the Z and the Zd are also set using the branching ratio limits in the H→ZZd→4ℓ search, and are in the range (1.5--8.7)×10−4 for 15Higgs portal coupling parameter, controlling the strength of the coupling of the Higgs boson to dark vector bosons, are set in the range (2--3)×10−5 and (1--10)×10−4 respectively, at 95 % confidence level assuming the Standard Model Higgs boson production cross sections, for Zd masses between 15 and 60 GeV.

Search for Dark Matter in Events with Missing Transverse Momentum and a Higgs Boson Decaying to Two Photons in pp Collisions at root s=8 TeV with the ATLAS Detector

Results of a search for new phenomena in events with large missing transverse momentum and a Higgs boson decaying to two photons are reported. Data from proton--proton collisions at a center-of-mass energy of 8 TeV and corresponding to an integrated luminosity of 20.3 fb−1 have been collected with the ATLAS detector at the LHC. The observed data are well described by the expected Standard Model backgrounds. Upper limits on the cross section of events with large missing transverse momentum and a Higgs boson candidate are also placed. Exclusion limits are presented for models of physics beyond the Standard Model featuring dark-matter candidates.

Combined measurement of the Higgs Boson Mass in pp collisions at root s=7 and 8 TeV with the ATLAS and CMS experiments

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for the Higgs boson in the H-->WW(*)-->l(+)nul(-)nu decay channel in pp collisions at radicals=7 TeV with the ATLAS detector

A search for the Higgs boson has been performed in the H-->WW(*)-->l(+)nul(-)nu[over ] channel (l=e/mu) with an integrated luminosity of 2.05 fb(-1) of pp collisions at radicals=7 TeV collected with the ATLAS detector at the Large Hadron Collider. No significant excess of events over the expected background is observed and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 110 GeVHiggs boson with a mass 145

Search for a standard model Higgs boson in the H→ZZ→ℓ(+)ℓ(-)νν decay channel with the ATLAS detector

A search for a heavy standard model Higgs boson decaying via H→ZZ→→ℓ(+)ℓ(-)νν, where ℓ=e, μ, is presented. It is based on proton-proton collision data at √s=7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340