Searches for Heavy Higgs Bosons in Two-Higgs-doublet Models and for $t2!h$ Decay Using Multilepton and Diphoton Final States in $pp$ Collisions at 8 TeV.
Searches for Heavy Higgs Bosons in Two-Higgs-doublet Models and for $t2!h$ Decay Using Multilepton and Diphoton Final States in $pp$ Collisions at 8 TeV.

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Published: 2014

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Searches are presented for heavy scalar (H) and pseudoscalar (A) Higgs bosons posited in the two doublet model (2HDM) extensions of the standard model (SM). These searches are based on a data sample of pp collisions collected with the CMS experiment at the LHC at a center-of-mass energy of √s=8 TeV and corresponding to an integrated luminosity of 19.5 fb-1. The decays H→hh and A→Zh, where h denotes an SM-like Higgs boson, lead to events with three or more isolated charged leptons or with a photon pair accompanied by one or more isolated leptons. Our search results are presented in terms of the H and A production cross sections times branching fractions and are further interpreted in terms of 2HDM parameters. We place 95% C.L. cross section upper limits of approximately 7 pb on [sigma]B for H→hh and 2 pb for A→Zh. Furthermore, the results of a search for the rare decay of the top quark are presented; this results in a charm quark and an SM Higgs boson,t→ch, the existence of which would indicate a nonzero flavor-changing Yukawa coupling of the top quark to the Higgs boson. We place a 95% C.L. upper limit of 0.56% on B(t→ch).

Searches for Heavy Higgs Bosons in Two-Higgs-doublet Models and for $t{u2192}ch$ Decay Using Multilepton and Diphoton Final States in $pp$ Collisions at 8 TeV.
Searches for Heavy Higgs Bosons in Two-Higgs-doublet Models and for $t{u2192}ch$ Decay Using Multilepton and Diphoton Final States in $pp$ Collisions at 8 TeV.

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Published: 2014

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Searches are presented for heavy scalar (H) and pseudoscalar (A) Higgs bosons posited in the two doublet model (2HDM) extensions of the standard model (SM). These searches are based on a data sample of pp collisions collected with the CMS experiment at the LHC at a center-of-mass energy of √s=8 TeV and corresponding to an integrated luminosity of 19.5 fb-1. The decays H→hh and A→Zh, where h denotes an SM-like Higgs boson, lead to events with three or more isolated charged leptons or with a photon pair accompanied by one or more isolated leptons. Our search results are presented in terms of the H and A production cross sections times branching fractions and are further interpreted in terms of 2HDM parameters. We place 95% C.L. cross section upper limits of approximately 7 pb on ?B for H→hh and 2 pb for A→Zh. Furthermore, the results of a search for the rare decay of the top quark are presented; this results in a charm quark and an SM Higgs boson,t→ch, the existence of which would indicate a nonzero flavor-changing Yukawa coupling of the top quark to the Higgs boson. We place a 95% C.L. upper limit of 0.56% on B(t→ch).

Search for Higgs Bosons Predicted in Two-Higgs-doublet Models Via Decays to Tau Lepton Pairs in 1.96-TeV P Anti-p Collisions
Search for Higgs Bosons Predicted in Two-Higgs-doublet Models Via Decays to Tau Lepton Pairs in 1.96-TeV P Anti-p Collisions

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Published: 2009

Total Pages: 7

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We present the results of a search for Higgs bosons predicted in two-Higgs-doublet models, in the case where the Higgs bosons decay to tau lepton pairs, using 1.8 fb−1 of integrated luminosity of p{bar p} collisions recorded by the CDF II experiment at the Fermilab Tevatron. Studying the mass distribution in events where one or both tau leptons decay leptonically, no evidence for a Higgs boson signal is observed. The result is used to infer exclusion limits in the two-dimensional space of tan [beta] versus m{sub A} (the ratio of the vaccum expectation values of the two Higgs doublets and the mass of the pseudoscalar boson, respectively).

Heavy Higgs Boson Search Via H->ZA->ZZh
Heavy Higgs Boson Search Via H->ZA->ZZh

Author: Zhangqier Wang

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Published: 2020

Total Pages: 0

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The discovery of a 125GeV Higgs boson at the Large Hadron Collider strongly motivates direct searches for additional Higgs bosons. This thesis describes a search for additional Higgs bosons via Higgs cascade production gg -> H-> ZA ->ZZh, including my phenomenology work as well as the experimental result using proton-protoncollision data collected at [square root s] = 13 TeV with the CMS experiment at the CERN LHC. In type I two Higgs doublet models there is a large region of parameter space at tan [beta] [greater than or similar to] 5 that is currently unconstrained experimentally. The phenomenology shows that the process gg -> H-> ZA ->ZZh can be sensitive in this region,and can be the discovery mode for an extended Higgs sector at the LHC. There are totally 9 promising decay modes for the ZZh state, and the most sensitive final states are [ell][ell][ell][ell]bb, [ell][ell]jjbb, [ell][ell][nu][nu][gamma][gamma] and [ell][ell][ell][ell] + missing energy. The result is presented in terms of 14 TeV projection with integrated luminosity of 300 fb−1 and 3000 fb−1 . The experimental analysis considers the four-lepton and two b-tagged jets final state, resulting from leptonic decays of the two Z bosons and decay of the Higgs bosons to b-quarks, which was found to be the mostsensitive channel in the phenomenological study. The data used in the analysis was collected by the CMS experiment from 35.9 fb−1 of proton-proton collisions at [squareroot s] =13 TeV produced at the Large Hadron Collider in 2016. Upper limits at 95% confidence level are obtained on the cross section of ZZh production in Type I 2HDM scenarios. The cascade decay channel considered in this analysis adds unique sensitivity to some regions of the parameter space within the two-Higgs-doublet-model.

Search for a CP-odd Higgs Boson Decaying to Zh in Pp Collisions at {u221A}s
Search for a CP-odd Higgs Boson Decaying to Zh in Pp Collisions at {u221A}s

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Published: 2015

Total Pages: 21

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A search for a heavy, CP-odd Higgs boson, A, decaying into a Z boson and a 125 GeV Higgs boson, h, with the ATLAS detector at the LHC is presented. The search uses proton–proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3fb-1. Decays of CP-even h bosons to ?? or bb pairs with the Z boson decaying to electron or muon pairs are considered, as well as h → bb decays with the Z boson decaying to neutrinos. No evidence for the production of an A boson in these channels is found and the 95% confidence level upper limits derived for ?(gg → A) × BR(A → Zh) × BR(h → f¯f) are 0.098–0.013pb for f = ? and 0.57–0.014 pb for f = b in a range of mA=220–1000 GeV. The results are combined and interpreted in the context of two-Higgs-doublet models.

Search for Heavy Resonances Decaying to Two Higgs Bosons in Final States Containing Four B Quarks
Search for Heavy Resonances Decaying to Two Higgs Bosons in Final States Containing Four B Quarks

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Published: 2016

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A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at sqrt(s)=8 TeV. The data correspond to an integrated luminosity of 19.7 inverse femtobarns. The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t-tbar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95% confidence level for the product of the production cross section and branching fraction sigma(gg to X) B(X to HH to b-bbar b-bbar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with a mass scale Lambda[R] = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV.

Search for New Light Higgs Bosons in Boosted Tau Final States with the CMS Experiment
Search for New Light Higgs Bosons in Boosted Tau Final States with the CMS Experiment

Author: Francesca Shun-Ning Annarosa Ricci-Tam

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Published: 2016

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ISBN-13: 9781339825892

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In this dissertation, I present a search for non-standard decays of a Standard Model-like Higgs boson to pairs of light bosons, as predicted in models with extended Higgs sectors. In two Higgs doublet models, including the next-to-minimal supersymmetric standard model, the Higgs boson can decay into a pair of light pseudoscalars a. In this search, the gluon fusion, W and Z associated Higgs, and vector boson fusion production channels for the Higgs are all considered, and the decay H->aa with a->[tau][tau] is reconstructed from the tau decay products. The final state is characterized by one isolated high p[subscript]T muon plus at least one highly boosted pair of taus, of which one of the taus is required to decay to a muon.Using 19.7 fb−1 of 8 TeV center of mass pp collision data recorded by the Compact Muon Solenoid experiment at the Large Hadron Collider, a counting experiment is performed in a region of high di-tau invariant mass. We have found no excess of events above the Standard Model backgrounds, and the observed data is used to set upper limits on the branching ratio Br(H->aa)Br2(a->[tau][tau]). These results are equally applicable to decays of the SM-like Higgs boson to a pair of light scalars h.

Search for Light Bosons in Decays of the 125 GeV Higgs Boson in Proton-proton Collisions at Sqrt(s)
Search for Light Bosons in Decays of the 125 GeV Higgs Boson in Proton-proton Collisions at Sqrt(s)

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Published: 2017

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A search is presented for decays beyond the standard model of the 125 GeV Higgs bosons to a pair of light bosons, based on models with extended scalar sectors. Light boson masses between 5 and 62.5 GeV are probed in final states containing four tau leptons, two muons and two b quarks, or two muons and two tau leptons. The results are from data in proton-proton collisions corresponding to an integrated luminosity of 19.7 inverse-femtobarns, accumulated by the CMS experiment at the LHC at a center-of-mass energy of 8 TeV. No evidence for such exotic decays is found in the data. Upper limits are set on the product of the cross section and branching fraction for several signal processes. The results are also compared to predictions of two-Higgs-doublet models, including those with an additional scalar singlet.

Constraints on New Phenomena Via Higgs Boson Couplings and Invisible Decays with the ATLAS Detector
Constraints on New Phenomena Via Higgs Boson Couplings and Invisible Decays with the ATLAS Detector

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Published: 2015

Total Pages: 52

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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 [gamma][gamma], ZZ, W W , Z[gamma], bb, [tau] [tau] , and [mu][mu] 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. The 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 [gamma][gamma] and ZZ decay modes, a lower limit is set on the pseudoscalar Higgs boson mass of mA > 370 GeV in the "hMSSM" simplified Minimal Supersymmetric Standard Model. Results from direct searches for heavy Higgs bosons are also interpreted in the hMSSM. Finally, 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. As a result, 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 Search for Charged Higgs Boson Decays of the Top Quark Using Hadronic Decays of the Tau Lepton in Proton-antiproton Collisions at Square Root S
A Search for Charged Higgs Boson Decays of the Top Quark Using Hadronic Decays of the Tau Lepton in Proton-antiproton Collisions at Square Root S

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Published: 2000

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The Standard Model predicts the existence of one neutral scalar Higgs boson, which is a remnant of the mechanism that breaks the SU(2)[sub L]xU(1)[sub Y] electroweak symmetry and generates masses for the heavy vector bosons and fermions. Many extensions to the Standard Model predict two or more Higgs doublets, resulting in a larger spectrum of Higgs bosons including a charged Higgs boson (H[sup [+-]]). For a light charged Higgs boson mass, the top decay into a charged Higgs boson and bottom quark might occur. This thesis presents results of a direct search for this top quark decay mode via the charged Higgs decay to a tau lepton and tau-neutrino, using the hadronic decays of the tau leptons. The search data consist of 100 pb[sup -1] of Run 1 data collected between 1992-1995 at the CDF detector, from p[anti p] collisions at a center-of-mass energy of 1.8 TeV produced at Fermilab's Tevatron accelerator. A total of seven events are observed in two search channels with an expected background contribution of 7.4[+-]2.0 events coming from fake taus (5.4[+-]1.5), heavy vector boson decays with jets (1.9[+-]1.3) and dibosons(0.08[+-]0.06). Lacking evidence for a signal, we set limits on charged Higgs production at the 95% confidence level in the charged Higgs mass plane versus tan[beta](a parameter of the theory) for a top quark mass of 175 GeV/c[sup 2] and for top production cross sections ([sigma][sub t[anti t]]) of 5.0 and 7.5 pb, assuming the Type-II Two-Higgs-Doublet-Model. For large tan[beta], this analysis excludes a charged Higgs boson of mass below 147(158)GeV/c[sup 2] for [sigma][sub t[anti t]]=5.0(7.5)pb. Using the Standard Model measured top quark cross section from CDF, this limit increases to 168 GeV/c[sup 2] and we also exclude a branching fraction of top decays via this charged Higgs mode of greater than 43% for charged Higgs masses below 168 GeV/c[sup 2].