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Higgs boson potential at colliders: Status and perspectives
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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.
A Historical Profile of the Higgs Boson
The Higgs boson was postulated in 1964, and phenomenological studies of its possible production and decays started in the early 1970s, followed by studies of its possible productionin e{sup +} e{sup -}, {anti p}p and pp collisions, in particular. Until recently, the most sensitive searches for the Higgs boson were at LEP between 1989 and 2000, which have been complemented bysearches at the Fermilab Tevatron. The LHC has recently entered the hunt, excluding a Higgs boson over a large range of masses and revealing a tantalizing hint in the range 119 to125 GeV, and there are good prospects that the existence or otherwise of the Higgs boson will soon be established. One of the most attractive possibilities is that the Higgs bosonis accompanied by supersymmetry, though composite options have yet to be excluded. This article reviews some of the key historical developments in Higgs physics over the past half-century.
Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector
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Supersymmetric Exotic Decays of the 125 GeV Higgs Boson
We reveal a set of novel decay topologies for the 125 GeV Higgs boson in supersymmetry which are initiated by its decay into a pair of neutralinos, and discuss their collider search strategies. This category of exotic Higgs decays are characterized by the collider signature: visible objects + $\mbox{${\not\! E}_{\rm T}$}$, with $\mbox{${\not\! E}_{\rm T}$}$ dominantly arising from escaping dark matter particles. Their benchmark arises naturally in the Peccei-Quinn symmetry limit of the MSSM singlet-extensions, which is typified by the co-existence of three light particles: singlet-like scalar $h_1$ and pseudoscalar $a_1$, and singlino-like neutralino $\chi_1$, all with masses of $\lesssim 10$ GeV, and the generically suppression of the exotic decays of the 125 GeV Higgs boson $h_2\to h_1 h_1$, $a_1a_1$ and $\chi_1\chi_1$, however. As an illustration, we study the decay topology: $h_2 \to \chi_1 \chi_2$, where the bino-like $\chi_2$ decays to $h_1 \chi_1$ or $a_1 \chi_1$, and $h_1/a_1 \to f\bar f$, with $f\bar f = \mu^+\mu^-$, $b\bar b$. In the di-muon case ($m_{h_1/a_1} \sim 1$ GeV), a statistical sensitivity of $\frac{S}{\sqrt{B}} > 6 \sigma$ can be achieved easily at the 8 TeV LHC, assuming $\frac{\sigma(pp \rightarrow W h_2)}{\sigma(pp \rightarrow W h_{\rm SM})} {\rm Br}(h_2 \to \mu^+\mu^- \chi_1 \chi_1)=0.1$. In the $b\bar b$ case ($m_{h_1/a_1} \sim 45$ GeV), 600 fb$^{-1}$ data at the 14 TeV LHC can lead to a statistical sensitivity of $\frac{S}{\sqrt{B}} > 5 \sigma$, assuming $\frac{\sigma(pp \rightarrow Z h_2)}{\sigma(pp \rightarrow Z h_{\rm SM})} {\rm Br}(h_2 \to b\bar b \chi_1 \chi_1)=0.5$. These exotic decays open a new avenue for exploring new physics couplings with the 125 GeV Higgs boson at colliders.
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. Thus, 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.
Search for heavy resonances decaying into a W or Z boson and a Higgs boson in final states with leptons and b -jets in 36 fb − 1 of s = 13 TeV p p collisions with the ATLAS detector
CERN-ATLAS. Search for heavy resonances decaying into a W or Z boson and a Higgs boson in final states with leptons and b-jets in 36 1/fb of 13 TeV pp collisions with the ATLAS detector
A Search for Dark Higgs Bosons
Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs boson using 516 fb{sup -1} of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the Standard Model-dark sector mixing angle and the dark sector coupling constant.
Search for Higgs bosons in supersymmetric cascade decays and neutralino dark matter
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Search for heavy resonances decaying into a W or Z boson and a Higgs boson in final states with leptons and b -jets in 36 fb -1 of $ \sqrt{s}=13 $ TeV pp collisions with the ATLAS detector
Here, a search is conducted for new resonances decaying into a W or Z boson and a 125 GeV Higgs boson in the $v\bar{v}$$b\bar{b}$, ℓ ± ν$b\bar{b}$, and ℓ + ℓ - $b\bar{b}$ final states, where ℓ ± = e ± or μ ± , in pp collisions at $\sqrt{s}$ =13 TeV. The data used correspond to a total integrated luminosity of 36.1 fb -1 collected with the ATLAS detector at the Large Hadron Collider during the 2015 and 2016 data-taking periods. The search is conducted by examining the reconstructed invariant or transverse mass distributions of W h and Zh candidates for evidence of a localised excess in the mass range of 220 GeV up to 5 TeV. No significant excess is observed and the results are interpreted in terms of constraints on the production cross-section times branching fraction of heavy W' and Z' resonances in heavy-vector-triplet models and the CP-odd scalar boson A in two-Higgs-doublet models. Upper limits are placed at the 95% confidence level and range between 9.0 × 10 -4 pb and 7.3 × 10 -1 pb depending on the model and mass of the resonance.
Search for light pseudoscalar boson pairs produced from Higgs boson decays using the 4τ and 2μ2τ final states in proton-proton collisions at $\sqrt{s}=13$ TeV
A search for a pair of light pseudoscalar bosons (a 1 ) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a 1 decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a1 boson mass probed in this study ranges from 4 to 15 GeV. The data sample was recorded by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponds to an integrated luminosity of 138 fb −1 . No excess above standard model (SM) expectations is observed. The study combines the 4τ and 2μ2τ channels to set upper limits at 95% confidence level (CL) on the product of the Higgs boson production cross section and the branching fraction to the 4τ final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a 1 boson is assumed to have Yukawa-like couplings to fermions, with coupling strengths proportional to the respective fermion masses. The observed (expected) upper limits range between 0.007 (0.011) and 0.079 (0.066) across the mass range considered. The results are also interpreted in the context of models with two Higgs doublets and an additional complex singlet field (2HD+S). The tightest constraints are obtained for the Type III 2HD+S model. In this case, assuming the Higgs boson production cross section equals the SM prediction, values of the branching ratio for the Higgs boson decay into a pair of a1 bosons exceeding 16% are excluded at 95% CL for a1 boson masses between 5 and 15 GeV and tan β > 2, with the exception of scenarios in which the a1 boson mixes with charm or bottom quark-antiquark bound states.
MSSM Higgs Boson Searches at the LHC: Benchmark Scenarios after the Discovery of a Higgs-like Particle
A Higgs-like particle with a mass of about 125.5 GeV has been discovered at the LHC. Within the current experimental uncertainties, this new state is compatible with both the predictions for the Standard Model (SM) Higgs boson and with the Higgs sector in the Minimal Supersymmetric Standard Model (MSSM). We propose new low-energy MSSM benchmark scenarios that, over a wide parameter range, are compatible with the mass and production rates of the observed signal. These scenarios also exhibit interesting phenomenology for the MSSM Higgs sector. We propose a slightly updated version of the well-known mh-max scenario, and a modified scenario (mh-mod), where the light CP-even Higgs boson can be interpreted as the LHC signal in large parts of the MA-tan \beta\ plane. Furthermore, we define a light stop scenario that leads to a suppression of the lightest CP-even Higgs gluon fusion rate, and a light stau scenario with an enhanced decay rate of h to \gamma\gamma\ at large tan \beta. We also suggest a \tau-phobic Higgs scenario in which the lightest Higgs can have suppressed couplings to down-type fermions. We propose to supplement the specified value of the \mu\ parameter in some of these scenarios with additional values of both signs. This has a significant impact on the interpretation of searches for the non SM-like MSSM Higgs bosons. We also discuss the sensitivity of the searches to heavy Higgs decays into light charginos and neutralinos, and to decays of the form H to hh. Finally, in addition to all the other scenarios where the lightest CP-even Higgs is interpreted as the LHC signal, we propose a low-MH scenario, where instead the heavy CP-even Higgs boson corresponds to the new state around 125.5 GeV.
Search for heavy resonances decaying into a Z or W boson and a Higgs boson in final states with leptons and b -jets in 139 fb –1 of pp collisions at $ \sqrt{s} $ = 13 TeV with the ATLAS detector
This article presents a search for new resonances decaying into a Z or W boson and a 125 GeV Higgs boson h, and it targets the $ν\bar{ν}b\bar{b}, l^{+} l^{-} b\bar{b}$, or $ll^{±} νb\bar{b}$ final states, where $\ell$ = e or µ, in proton-proton collisions at $\sqrt{s}$ = 13 TeV. The data used correspond to a total integrated luminosity of 139 fb –1 collected by the ATLAS detector during Run 2 of the LHC at CERN. The search is conducted by examining the reconstructed invariant or transverse mass distributions of Zh or W h candidates for evidence of a localised excess in the mass range from 220 GeV to 5 TeV. No significant excess is observed and 95% confidence-level upper limits between 1.3 pb and 0.3 fb are placed on the production cross section times branching fraction of neutral and charged spin-1 resonances and CP-odd scalar bosons. These limits are converted into constraints on the parameter space of the Heavy Vector Triplet model and the two-Higgs-doublet model.
Unburied Higgs boson: Jet substructure techniques for searching for Higgs’ decay into gluons
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Higgs boson decay to light jets at the LHC
We study here the Higgs boson $(h)$ decay to two light jets at the 14 TeV High-Luminosity-LHC (HL-LHC), where a light jet ($j$) represents any non-flavor tagged jet from the observational point of view. The decay mode $h\to gg$ is chosen as the benchmark since it is the dominant channel in the Standard Model (SM), but the bound obtained is further applicable to the light quarks $(j=u,d,s)$. We also estimate the achievable bounds on the decay branching fractions through the associated production $Vh\ (V=W^\pm,Z)$. Events of the Higgs boson decaying into heavy (tagged) or light (un-tagged) jets are correlatively analyzed. We find that with 3000 fb$^{-1}$ data at the HL-LHC, we should expect approximately $1\sigma$ statistical significance on the SM $Vh(gg)$ signal in this channel. This corresponds to a reachable upper bound ${\rm BR}(h\to jj) \leq 4~ {\rm BR}^{SM}(h\to gg)$ at $95\%$ confidence level. A consistency fit also leads to an upper bound ${\rm BR}(h\to cc) < 15~ {\rm BR}^{SM}(h\to cc)$ at $95\%$ confidence level. The estimated bound may be further strengthened by adopting multiple variable analyses, or adding other production channels.