Search for the Standard Model Higgs boson in the H → τ + τ − decay mode in $ \sqrt {s} = 7\,{\mathrm{TeV}} $ pp collisions with ATLAS

Abstract

Search for the Standard Model Higgs boson in the H → τ + τ − decay mode in √ s = 7 TeV pp collisions with ATLASThe ATLAS collaboration E-mail: atlas.publications@cern.ch Abstract: A search for the Standard Model Higgs boson decaying into a pair of τ leptons is reported. The analysis is based on a data sample of proton-proton collisions collected by the ATLAS experiment at the LHC and corresponding to an integrated luminosity of 4.7 fb −1 . No significant excess over the expected background is observed in the Higgs boson mass range of 100-150 GeV. The observed (expected) upper limits on the cross section times the branching ratio for H → τ + τ − are found to be between 2.9 (3.4) and 11.7 (8.2) times the Standard Model prediction for this mass range. Keywords: Hadron-Hadron ScatteringOpen Access, Copyright CERN, for the benefit of the ATLAS collaboration doi:10.1007/JHEP09(2012)070 The ATLAS collaboration 29 JHEP09(2012)070 IntroductionThe Higgs boson is the only fundamental particle in the Standard Model (SM) of particle physics that has not yet been observed. It is predicted by the Higgs mechanism [1-6], which in the SM gives mass to particles. The search for the Higgs boson is a centrepiece of the Large Hadron Collider (LHC) physics programme. An indirect constraint on the Higgs boson mass of m H < 185 GeV at the 95% confidence level (CL) has been set using global fits to electroweak precision data [7]. Direct searches at LEP and the Tevatron have placed exclusion limits at 95% CL for m H < 114.4 GeV and in the region 147 GeV < m H < 179 GeV [8, 9], respectively. The results of -1 - JHEP09(2012)070searches in various channels using data corresponding to an integrated luminosity of up to 5 fb −1 have recently been reported by both the ATLAS and CMS Collaborations [10,11] excluding the mass range between 112.9 GeV and 115.5 GeV and the region between 127 GeV and 600 GeV, again at the 95% CL.In the Higgs boson mass range 100-150 GeV, the H → τ + τ − decay mode is a promising channel for the search at the LHC with branching ratios between 8% and 1.8%. The H → τ + τ − search is complementary to searches with other decays in the same mass range and enhances the overall sensitivity. Also, if the Higgs boson is discovered, the measurement of the H → τ + τ − decay rate provides a test of the SM prediction for the τ Yukawa coupling.The process with the largest cross section to produce a SM Higgs boson at the LHC is gluon fusion gg → H. However, Higgs boson production via vector boson (W W , ZZ) fusion qq → qqH (VBF) and via Higgs-strahlung qq → V H, in association with a hadronically decaying vector boson (V = W or Z), are highly relevant as well because they lead to additional jets in the final state, which provide distinct experimental signatures. In particular the VBF topology of two high-energy jets with a large rapidity separation offers a good discrimination against background processes. For all production processes above, the Higgs boson is typically more boosted in the transverse plane if there are additional hig...

Search for the neutral Higgs bosons of the minimal supersymmetric standard model in pp collisions at $ \sqrt{s}=7 $ TeV with the ATLAS detector

“…The event yield of the embedded sample after the selection of the τ decay products is normalised to the corresponding event yield obtained in a simulated Z/γ * → τ + τ − sample. This procedure has been validated as described in references [7,61]. Systematic uncertainties on the normalisation and shape of the embedded sample are derived by propagating variations of the Z/γ * → µ + µ − event selection and the muon energy subtraction procedure through the τ -embedding process.…”

Probing the Higgs portal at the LHC through resonant di-Higgs production

“…For di-Higgs production, the h 1 decaying to the bb pair takes the place of the high-p T jet, so we expect the use of the collinear approximation to be reasonably reliable in the case of our analysis (see also Ref. [45]). …”

“…Further reduction of the Z backgrounds could be achieved by considering only eμ pairs as in Ref. [45]. Doing so in the present case, however, leads to a loss of signal without significantly improving the final S= ffiffiffiffiffiffiffiffiffiffiffiffi S þ B p .…”

“…A crucial step in this direction is the reconstruction of the invariant mass of the bb and τ þ τ − pairs that should individually reproduce the h 1 peak. The missing mass calculator technique [43] commonly used by the ATLAS and CMS Collaborations [44,45] to reconstruct the invariant mass of a τ þ τ − system from a decaying resonance relies on maximum likelihood methods that are not possible to implement in the present analysis. Alternatively, we use the collinear approximation [46] to reconstruct the ditau invariant mass, which is used in experimental analyses of boosted resonances [45].…”

“…[45]. We, thus, consider bb plus (a) two leptonically decaying τs ("τ lep τ lep "); (b) one leptonically decaying and one hadronically decaying τ ("τ lep τ had "); and (c) two hadronically decaying τ's ("τ had τ had ").…”