Looking for an invisible Higgs signal at the LHC

195

198

Abstract: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 → , 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. Conclusions 26The ATLAS collaboration 36 IntroductionThe ATLAS and CMS Collaborations at the Large Hadron Collider (LHC) announced the discovery of a particle consistent with a Higgs boson in 2012 [1,2]. Since then, the collaborations have together measured the mass of the particle to be about 125 GeV [3][4][5]. Studies of its spin and parity in bosonic decays have found it to be compatible with a J P = 0 + state [6][7][8]. Combined coupling fits of the measured Higgs boson production and decay rates within the framework of the Standard Model (SM) have found no significant deviation from the SM expectations [4,9, 10]. These results strongly suggest that the newly discovered particle is indeed a Higgs boson and that a non-zero vacuum expectation value of a Higgs doublet is responsible for electroweak (EW) symmetry breaking [11][12][13].The observed CP-even Higgs boson is denoted as h throughout this paper. A crucial question is whether there is only one Higgs doublet, as postulated by the SM, or whether the Higgs sector is more complex, for example with a second doublet leading to more than one Higgs boson of which one has properties similar to those of the SM Higgs -1 - JHEP11(2015)206boson, as predicted in many theories beyond the Standard Model (BSM). 1 The "hierarchy problem" regarding the naturalness of the Higgs boson mass, the nature of dark matter, and other open questions that the SM is not able to answer also motivate the search for additional new particles and interactions. Astrophysical observations provide strong evidence of dark matter that could be explained by the e...

Section: Direct Searches For Invisible Decaysmentioning

confidence: 99%

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

Aad

Bergeås

Brenner

et al. 2015

195

198

“…via the dijets plus missing energy signal. Finally, it was estimated that ξ 2 ≈ 0.25 would be probed at 5σ by the LHC with 300 fb −1 at 14 TeV [49], also via dijets plus missing energy. Both of these studies also considered the LHC sensitivity to Higgsstrahlung process, where the Higgs is invisible and the Z decays leptonically, but found it to be a weaker probe of ξ 2 .…”

Section: Missing Energy At the Lhcmentioning

confidence: 99%

Bulk stabilization, the extra-dimensional Higgs portal and missing energy in Higgs events

Diener

Burgess

2013

To solve the hierarchy problem, extra-dimensional models must explain why the new dimensions stabilize to the right size, and the known mechanisms for doing so require bulk scalars that couple to the branes. Because of these couplings the energetics of dimensional stabilization competes with the energetics of the Higgs vacuum, with potentially observable effects. These effects are particularly strong for one or two extra dimensions because the bulkHiggs couplings can then be super-renormalizable or dimensionless. Experimental reach for such extra-dimensional Higgs 'portals' are stronger than for gravitational couplings because they are less suppressed at low-energies. We compute how Higgs-bulk coupling through such a portal with two extra dimensions back-reacts onto properties of the Higgs boson. When the KK mass is smaller than the Higgs mass, mixing with KK modes results in an invisible Higgs decay width, missing-energy signals at high-energy colliders, and new mechanisms of energy loss in stars and supernovae. Astrophysical bounds turn out to be complementary to collider measurements, with observable LHC signals allowed by existing constraints. We comment on the changes to the Higgs mass-coupling relationship caused by Higgs-bulk mixing, and how the resulting modifications to the running of Higgs couplings alter vacuum-stability and triviality bounds.

“…The LHC prospects of determining the invisible Higgs BR have been analyzed in refs. [21][22][23][24][25][26][27][28][29][30]. The current experimental limits for a 125 GeV invisible Higgs BR are < 0.65 from ATLAS [31] and < 0.75 from CMS [32] at 95% CL derived from the direct search pp → Zh → ℓℓ / E T .…”

Section: Jhep10(2013)221mentioning

confidence: 99%

“…As manifested in these contour plots, the minimum χ 2 -value is obtained for ε = 0, 0.037 and 0.04 for BP1, BP2 and BP3 respectively and intermediate values of tan β around [30][31][32][33][34][35][36][37][38][39][40] JHEP10 (2013) Figure 4. 1σ and 2σ contours for ε and tan β from χ 2 minimization obtained for BP2.…”

Section: The Invisible Decay Width and Current Datamentioning

confidence: 99%

“…The possibility of an invisible Higgs signature at the LHC has been explored both theoretically [22,23,[26][27][28][29][30] and experimentally [31,32,135]. These studies show that the most promising Higgs production channel for detecting an invisibly decaying Higgs is the vector boson fusion (VBF), and the next promising channel is its associated production with Z.…”

Section: Collider Analysismentioning

confidence: 99%

See 1 more Smart Citation

Invisible Higgs decay in a supersymmetric inverse seesaw model with light sneutrino dark matter

Banerjee

Dev

Mondal

et al. 2013

Within the framework of a constrained Minimal Supersymmetric Standard Model (cMSSM) augmented by an MSSM singlet-pair sector to account for the non-zero neutrino masses by inverse seesaw mechanism, the lightest supersymmetric particle (LSP) can be a mixed sneutrino with mass as small as 50 GeV, satisfying all existing constraints, thus qualifying as a light dark matter candidate. We study the possibility of the lightest neutral Higgs boson in this model decaying invisibly into a pair of sneutrino LSPs, thereby giving rise to novel missing energy signatures at the LHC. We perform a two-parameter global analysis of the LHC Higgs data available till date to determine the optimal invisible Higgs branching fraction in this scenario, and obtain a 2σ (1σ) upper limit of 0.25 (0.15). A detailed cut-based analysis is carried out thereafter, demonstrating the viability of our proposed signal vis-a-vis backgrounds at the LHC.