Higgs Boson Branching Ratios Research Articles

Prospects for the high-luminosity LHC

This note reviews the main physics topics accessible with the high-luminosity LHC program (HL-LHC). It should deliver p-p collisions at s=14TeV with an integrated luminosity of 3000fb−1. Results are presented in perspective with the previous period with ten times less luminosity. The ATLAS and CMS collaborations released expected results for this program assuming similar detector performance as today within more difficult conditions. The Higgs boson branching ratios and couplings to fermions/bosons will be measured at few percent level. The main discovery limits for the search of new particles or phenomena beyond the Standard Model are presented.

TESTING TIMES FOR SUPERSYMMETRY: LOOKING UNDER THE LAMP POST

We make a critical study of two highly-constrained models of supersymmetry — the constrained minimal supersymmetric standard model (cMSSM), and the nonuniversal Higgs mass (NUHM) model — in the light of the 125–126 GeV Higgs boson, the first observation of Bs→μμ at the LHCb, and the updated B → τν branching ratio at BELLE. It turns out that these models are still allowed by the experimental data, even if we demand that there be a light stop with mass less than 1.5 TeV. The only significant effects of all these constraints are to push the mass of the light stop above ~500 GeV, and to prefer the universal trilinear coupling A0to be large and negative. We calculate the Higgs boson branching ratios to WW, ZZ, ττ and γγ in these models and show that improved experimental limits on these could put them to the most stringent experimental tests yet.

A study of measurement precision of the Higgs boson branching ratios at the International Linear Collider

Precise measurement of Higgs boson couplings is an important task for International Linear Collider (ILC) experiments and will facilitate the understanding of the particle mass generation mechanism. In this study, the measurement accuracies of the Higgs boson branching fractions to the $b$ and $c$ quarks and gluons, $\Delta Br(H\to b\bar{b},\sim c\bar{c},\sim gg)/Br$, were evaluated with the full International Large Detector model (\texttt{ILD\_00}) for the Higgs mass of 120 GeV at the center-of-mass (CM) energies of 250 and 350 GeV using neutrino, hadronic and leptonic channels and assuming an integrated luminosity of $250 {\rm fb^{-1}}$, and an electron (positron) beam polarization of -80% (+30%). We obtained the following measurement accuracies of the Higgs cross section times branching fraction ($\Delta (\sigma \cdot Br)/\sigma \cdot Br$) for decay of the Higgs into $b\bar{b}$, $c\bar{c}$, and $gg$; as 1.0%, 6.9%, and 8.5% at a CM energy of 250 GeV and 1.0%, 6.2%, and 7.3% at 350 GeV, respectively. After the measurement accuracy of the cross section ($\Delta\sigma/\sigma$) was corrected using the results of studies at 250 GeV and their extrapolation to 350 GeV, the derived measurement accuracies of the branching fractions ($\Delta Br/Br$) to $b\bar{b}$, $c\bar{c}$, and gg were 2.7%, 7.3%, and 8.9% at a CM energy of 250 GeV and 3.6%, 7.2%, and 8.1% at 350 GeV, respectively.

Reproducing the Higgs boson data with vector-like quarks

Vector-Like (VL) quarks arise in the main alternatives to the supersymmetric extensions of the Standard Model (SM). Given the experimental possibility of a 125 GeV Higgs boson with rates significantly different from the SM expectations, it is motivating to study the effects of VL quarks on the Higgs boson cross sections and branching ratios. We perform a systematic search for the minimal field contents and gauge group representations of VL quarks able to significantly improve the fit of the measured Higgs rates, and simultaneously, to satisfy the direct constraints on VL quark masses as well as the electro-weak precision tests. In particular, large enhancements can be achieved in certain diphoton channels – as pointed out by both the ATLAS and CMS Collaborations – optimizing then the Higgs rate fit. This is a consequence of the introduction of VL quarks, with high electric charges of 8/3 or −7/3, which are exchanged in the Higgs-to-diphoton loop. Interestingly, the field contents and formal Higgs couplings obtained here are similar to those of scenarios in warped/composite frameworks arising from different motivations. The various exotic-charge quarks predicted, possibly below the TeV scale, might lead to a rich phenomenology soon at the LHC.

Branching ratio of the invisible decays of the lightest Higgs boson h0 in the MSSM

The Supersymmetric models predicts the existence of light neutralinos with masses around 50 GeV as good candidates for detection of physics beyond the Standard Model, as well as other supersymmetric particles for different channels of Higgs boson decays. It this work, we presented the branching ratios of the lightest Higgs boson to neutralinos and charginos in the context of the Minimal Supersymmetric Standard Model. Although the invisible modes have been studied previously, is not known in detail the region of parameter space for supersymmetric sector where the mode reaches a significant branching ratio. We presented the analysis the parameters space looking for these regions by sampling techniques.

HiggsBounds 2. 0. 0: Confronting neutral and charged Higgs sector predictions with exclusion bounds from LEP and the Tevatron

HiggsBounds 2. 0. 0 is a computer code which tests both neutral and charged Higgs sectors of arbitrary models against the current exclusion bounds from the Higgs searches at LEP and the Tevatron. As input, it requires a selection of model predictions, such as Higgs masses, branching ratios, effective couplings and total decay widths. HiggsBounds 2. 0. 0 then uses the expected and observed topological cross section limits from the Higgs searches to determine whether a given parameter scenario of a model is excluded at the 95% C.L. by those searches. Version 2.0.0 represents a significant extension of the code since its first release (1.0.0). It includes now 28/53 LEP/Tevatron Higgs search analyses, compared to the 11/22 in the first release, of which many of the ones from the Tevatron are replaced by updates. As a major extension, the code allows now the predictions for (singly) charged Higgs bosons to be confronted with LEP and Tevatron searches. Furthermore, the newly included analyses contain LEP searches for neutral Higgs bosons ( H) decaying invisibly or into (non-flavour tagged) hadrons as well as decay-mode independent searches for neutral Higgs bosons, LEP searches via the production modes τ + τ − H and b b ¯ H , and Tevatron searches via t t ¯ H . Also, all Tevatron results presented at the ICHEPʼ10 are included in version 2.0.0. As physics applications of HiggsBounds 2. 0. 0 we study the allowed Higgs mass range for model scenarios with invisible Higgs decays and we obtain exclusion results for the scalar sector of the Randall–Sundrum model using up-to-date LEP and Tevatron direct search results. Program summary Program title: HiggsBounds Catalogue identifier: AEFF_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEFF_v2_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: GNU General Public Licence version 3 No. of lines in distributed program, including test data, etc.: 74 005 No. of bytes in distributed program, including test data, etc.: 1 730 996 Distribution format: tar.gz Programming language: Fortran 77, Fortran 90 (two code versions are offered). Classification: 11.1. Catalogue identifier of previous version: AEFF_v1_0 Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 138 External routines: HiggsBounds requires no external routines/libraries. Some sample programs in the distribution require the programs FeynHiggs 2.7.1 or CPsuperH2.2 to be installed. Does the new version supersede the previous version?: Yes Nature of problem: Determine whether a parameter point of a given model is excluded or allowed by LEP and Tevatron neutral and charged Higgs boson search results. Solution method: The most sensitive channel from LEP and Tevatron searches is determined and subsequently applied to test this parameter point. The test requires as input, model predictions for the Higgs boson masses, branching ratios and ratios of production cross sections with respect to reference values. Reasons for new version: This version extends the functionality of the previous version. Summary of revisions: List of included Higgs searches has been expanded, e.g. inclusion of (singly) charged Higgs boson searches. The input required from the user has been extended accordingly. Restrictions: Assumes that the narrow width approximation is applicable in the model under consideration and that the model does not predict a significant change to the signature of the background processes or the kinematical distributions of the signal cross sections. Running time: About 0.01 seconds (or less) for one parameter point using one processor of an Intel Core 2 Quad Q6600 CPU at 2.40 GHz for sample model scenarios with three Higgs bosons. It depends on the complexity of the Higgs sector (e.g. the number of Higgs bosons and the number of open decay channels) and on the code version.

Higgs boson decays and production in the left–right twin Higgs model

The left–right twin Higgs model predicts one neutral Higgs boson ϕ0 and it acquires mass mϕ0∼μr with the μ term, which can be lighter than half the SM-like Higgs boson mass in a portion of parameter space. Thus, the SM-like Higgs boson h can dominantly decay into a pair of light neutral Higgs bosons especially when mh is below the WW threshold. First, we examine the branching ratios of the SM-like Higgs boson decays and find that the new decay mode h→ϕ0ϕ0 is dominant for the case of mh>2mϕ0. Then we study the production via gluon fusion followed by the decay into two photons or two weak gauge bosons and found that the production rate can be significantly suppressed for some part of parameter space. Finally, we comparatively study the process γγ→h→bb¯ at ILC in the cases of mh>2mϕ0 and mh<2mϕ0, respectively. We find that these predictions can significantly deviated from the SM predictions, e.g., the gluon–gluon fusion channel, in the cases of mh>2mϕ0 and mh<2mϕ0, can be suppressed by about 80% and 45%, respectively. Therefor, it is possible to probe the left–right twin Higgs model via these Higgs boson production processes at the LHC experiment or in the future ILC experiment.

Many light Higgs bosons in the next-to-minimal supersymmetric model

The next-to-minimal supersymmetric model with a light doubletlike CP-odd Higgs boson and small tan{beta} can satisfy all experimental limits on Higgs bosons even with light superpartners. In these scenarios, the two lightest CP-even Higgs bosons, h{sub 1} and h{sub 2}, and the charged Higgs boson, h{sup +}, can all be light enough to be produced at CERN LEP and yet have decays that have not been looked for or are poorly constrained by existing collider experiments. The channel h{sub 1}{yields}a{sub 1}a{sub 1} with a{sub 1}{yields}{tau}{sup +}{tau}{sup -} or 2j is still awaiting LEP constraints for m{sub h{sub 1}}>86 or 82 GeV, respectively. LEP data may also contain e{sup +}e{sup -}{yields}h{sub 2}a{sub 1} events where h{sub 2}{yields}Za{sub 1} is the dominant decay, a channel that was never examined. Decays of the charged Higgs bosons are often dominated by H{sup {+-}}{yields}W{sup {+-}}{sup (}*{sup )}a{sub 1} with a{sub 1}{yields}gg, cc, and {tau}{sup +}{tau}{sup -}. This is a channel that has so far been ignored in the search for t{yields}h{sup +}b decays at the Tevatron. A specialized analysis might reveal a signal. The light a{sub 1} might be within the reach of B factories via {upsilon}{yields}{gamma}a{sub 1} decays. We study typical mass ranges and more » branching ratios of Higgs bosons in this scenario and compare these scenarios where the a{sub 1} has a large doublet component to the more general scenarios with arbitrary singlet component for the a{sub 1}. « less

Towards a measurement of the two-photon decay width of the Standard Model Higgs boson at a Photon Collider

A study of the measurement of the two photon decay width times the branching ratio of the Standard Model Higgs boson with a mass of 120 GeV in photon–photon collisions is presented, assuming a γ γ integrated luminosity of 80 fb−1 in the high energy part of the spectrum. The analysis is based on the reconstruction of the Higgs events produced in the γ γ→H process, followed by the decay of the Higgs into a $\mathrm{b}\bar{\mathrm{b}}$ pair. A statistical error of the measurement of the two-photon width, Γ(H→γ γ), times the branching ratio of the Higgs boson, BR $(\mathrm{H}\to \mathrm{b}\bar{\mathrm{b}})$ is found to be 2.1% for one year of data taking.

CP-violating Higgs boson mixing in chargino production at the muon collider

We study the pair-production of charginos in the CP-violating Minimal Supersymmetric Standard Model at center-of-mass energies around the heavy neutral Higgs boson resonances. If these resonances are nearly degenerate, as it can happen in the Higgs decoupling limit, radiatively induced scalar-pseudoscalar transitions can be strongly enhanced. The resulting mixing in the Higgs sector leads to large CP-violating effects, and a change of their mass spectrum. For longitudinally polarized muon beams, we analyze CP asymmetries which are sensitive to the interference of the two heavy neutral Higgs bosons. We present a detailed numerical analysis of the cross sections, chargino branching ratios, and the CP observables. We obtain sizable CP-asymmetries, which would be accessible in future measurements at a muon collider. Especially for intermediate values of the parameter \tan\beta, where the largest branching ratios of Higgs bosons into charginos are expected, this process allows to analyze the Higgs sector properties and its interaction to supersymmetric fermions.

Fundamental and composite scalars from extra dimensions

We discuss a scenario consisting of an effective 4D theory containing fundamental and composite fields. The strong dynamics sector responsible for the compositeness is assumed to be of extra dimensional origin. In the 4D effective theory the SM fermion and gauge fields are taken as fundamental fields. The scalar sector of the theory resembles a bosonic topcolor in the sense there are two scalar Higgs fields, a composite scalar field and a fundamental gauge-Higgs unification scalar. A detailed analysis of the scalar spectrum is presented in order to explore the parameter space consistent with experiment. It is found that, under the model assumptions, the acceptable parameter space is quite constrained. As a part of our phenomenological study of the model, we evaluate the branching ratio of the lightest Higgs boson and find that our model predicts a large FCNC mode h→tc, which can be as large as O(10−3). Similarly, a large BR for the top FCNC decay is obtained, namely BR(t→c+H)≃10−4.

Model-independent determination of the top Yukawa coupling from LHC and ILC

We show how a measurement of the process pp-->t tbar H + X at the LHC and a measurement of the Higgs boson branching ratios BR(H-->b bar) and BR(H-->W+W-) at a future linear electron positron collider can be combined to extract a model-independent measurement of the top quark Yukawa coupling. We find that for 120 GeV < m_H < 200 GeV a measurement precision of 15% including systematic uncertainties can be achieved for integrated luminosities of 300 fb-1 at the LHC and 500 fb-1 at the LC at a centre-of-mass energy of 350 GeV.

Lightest Higgs boson production at photon colliders in the two Higgs doublet model type III

The branching ratios of the lightest CP-even Higgs boson $h^0$, in the framework of the General Two Higgs Doublet Model are calculated. Different scenarios are presented taking into account constraints obtained in previous works on the flavor changing neutral currents factors. Plausible scenarios with flavour changing processes at tree level like $b \bar s$ and $t \bar c$ are analyzed for relevant region of parameters. The loop-induced Higgs couplings to photon pairs can be tested with a photon collider. The number of events of $h^0$ as a resonance in photon colliders are calculated taking into account its corresponding background signal in TESLA, CLIC and NLC.

LHC/LC Interplay in the MSSM Higgs Sector

The interplay of prospective experimental information from both the Large Hadron Collider (LHC) and the Linear Collider (LC) in the investigation of the MSSM Higgs sector is analyzed in the SPS~1a and SPS 1b benchmark scenarios. Combining LHC information on the heavy Higgs states of the MSSM with precise measurements of the mass and branching ratios of the lightest CP-even Higgs boson at the LC provides a sensitive consistency test of the MSSM. This allows to set bounds on the trilinear coupling A_t. In a scenario where LHC and LC only detect one light Higgs boson, the prospects for an indirect determination of M_A are investigated. In particular, the impact of the experimental errors of the other SUSY parameters is analyzed in detail. We find that a precision of about 20% (30%) can be achieved for M_A = 600 (800) GeV.

Weak isospin violations in charged and neutral Higgs couplings from supersymmetric loop corrections

Supersymmetric QCD and supersymmetric electroweak loop corrections to the violations of weak isospin to Yukawa couplings are investigated. Specifically it involves an analysis of the supersymmetric loop corrections to the Higgs couplings to the third generation quarks and leptons. Here we analyze the SUSY loop corrections to the charged Higgs couplings which are then compared with the supersymmetric loop corrections to the neutral Higgs couplings previously computed. It is found that the weak isospin violations can be quite significant, i.e, as much as 40-50% or more of the total loop correction to the Yukawa coupling. The effects of CP phases are also studied and it is found that these effects can either enhance or suppress the weak isospin violations. We also investigate the weak isospin violation effects on the branching ratio $BR(H^-\to\bar t b)/ BR(H^-\to \bar\nu_{\tau}\tau^-)$ and show that the effects are sensitive to CP phases. Thus an accurate measurement of this branching ratio along with the branching ratio of the neutral Higgs boson decays can provide a measure of weak isospin violation along with providing a clue to the presence of supersymmetry.

Search for ‘invisible’ Higgs signals at LHC via associated production with gauge bosons

A light Higgs boson with substantial branching ratio into invisible channels can occur in a variety of models with: light neutralinos, spontaneously broken lepton number, radiatively generated neutrino masses, additional singlet scalar(s) and/or right handed neutrinos in the extra dimensions of TeV scale gravity. We study the observability of the WH and ZH modes at LHC with H decaying invisibly, by carrying out a detailed simulation with two event generators (HERWIG and PYTHIA) and realistic detector simulations (GETJET and CMSJET). We find that the signal with ‘single lepton plus missing ET’ resulting from WH production suffers from a very large background due to the (off-shell) W∗ production via the Drell–Yan process. In contrast, the ZH mode provides a clean signal in the ‘dilepton plus missing ET’ channel. By exploiting this second signature, we show that invisible branching ratios of Higgs bosons, BRinv, larger than ∼0.42 (0.70) can be probed at 5σ level for MH=120 (160) GeV, respectively, assuming an accumulated luminosity of L=100 fb−1.

Testing anomalous gauge couplings of the Higgs boson via weak-boson scatterings at the CERN LHC

We propose a sensitive way to test the anomalous HVV couplings ${(V=W}^{\ifmmode\pm\else\textpm\fi{}},{Z}^{0})$ of the Higgs boson $(H),$ which can arise from either the dimension-3 effective operator in a nonlinearly realized Higgs sector or the dimension-6 effective operators in a linearly realized Higgs sector, via studying the VV scattering processes at the CERN LHC. The gold-plated pure leptonic decay modes of the final state weak bosons in the processes $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{VVjj}$ are studied. For comparison, we also analyze the constraints from the precision electroweak data, the expected precision of the measurements of the Higgs boson production rate, decay width and branching ratios at the Fermilab Tevatron run-2 and the CERN LHC, and the requirement of unitarity of the S matrix. We show that, with an integrated luminosity of $300{\mathrm{fb}}^{\ensuremath{-}1}$ and sufficient kinematical cuts for suppressing the backgrounds, studying the process $p\stackrel{\ensuremath{\rightarrow}}{p}{W}^{+}{W}^{+}j\stackrel{\ensuremath{\rightarrow}}{j}{l}^{+}\ensuremath{\nu}{l}^{+}\ensuremath{\nu}\mathrm{jj}$ can probe the anomalous HWW couplings at a few tens of percent level for the nonlinearly realized Higgs sector, and at the level of $0.01\char21{}0.08{\mathrm{TeV}}^{\ensuremath{-}1}$ for the linearly realized effective Lagrangian.

A CCD vertex detector for measuring Higgs boson branching ratios at a linear collider

We have studied a CCD vertex detector design for a future linear collider and report methods under consideration for radiation damage remediation in the linear collider environment. Noting the rich physics program available with a precise vertex detector, we report the expected precision on the Standard Model Higgs boson branching ratios with the described design and the efforts towards improving the topological vertex reconstruction algorithms.

Optimal observables to search for indirect supersymmetric QCD signals in Higgs boson decays

In this work we study the indirect effects of squarks and gluinos via supersymmetric QCD radiative corrections in the decays of Higgs particles within the minimal supersymmetric standard model. We consider a heavy supersymmetric spectrum and focus on the main nondecoupling effects. We propose a set of observables that are sensitive to these corrections and that will be accessible at the CERN Large Hadron Collider and Fermilab Tevatron. These observables are the ratios of Higgs boson branching ratios into quarks divided by the corresponding Higgs boson branching ratios into leptons, and both theoretical and experimental uncertainties are expected to be minimized. We show that these nondecoupling corrections are sizable for all the proposed observables in the large $\mathrm{tan}\ensuremath{\beta}$ region and are highly correlated. A global analysis of all these observables will allow the experiments to reach the highest sensitivity to indirect supersymmetric signals.

Decays of the MSSM Higgs bosons with explicitCPviolation

We study Higgs boson decays in the minimal supersymmetric standard model where the tree-level CP invariance of the Higgs potential is explicitly broken by loop effects of soft CP-violating Yukawa interactions related to scalar quarks of the third generation. The scalar-pseudoscalar mixing among two neutral CP-even Higgs bosons and one CP-odd Higgs boson due to explicit CP violation modifies their tree-level couplings to fermions, to the W^\pm and Z bosons and to Higgs bosons themselves significantly. We analyze the phenomenological impact of explicit CP violation on the branching ratios of the neutral Higgs boson decays in detail and discuss how to directly confirm the existence of explicit CP violation through \tau^+ \tau^- and t \bar{t} spin correlations in the decays of the neutral Higgs bosons into a tau-lepton pair and a top-quark pair.