pp(macro)-->tt(macro)H: a discovery mode for the Higgs boson at the Fermilab Tevatron

The production of a standard model Higgs boson in association with a top quark pair at the upcoming high luminosity run ( 15 fb(-1) integrated luminosity) of the Fermilab Tevatron ( square root of s = 2.0 TeV) is revisited. For Higgs masses below 140 GeV we demonstrate that the production cross section times branching ratio for H-->bb macro decays yields a significant number of events and that this mode is competitive with and complementary to the searches using pp(macro) -->WH,ZH associated production. For higher mass Higgs bosons the H-->W(+)W(-) decays are more difficult but have the potential to provide a few spectacular events.     

Search for the Higgs boson in H --> WW(*) decays in pp collisions at square root of 1.96 TeV

We present a search for the standard model Higgs boson in H --> WW(*) decays with e+e-, e+/-mu-/+, and mu+mu- final states in pp collisions at a center-of-mass energy of square root of s = 1.96 TeV. The data, collected from April 2002 to June 2004 with the D0 detector, correspond to an integrated luminosity of 300-325 pb(-1), depending on the final state. The number of events observed is consistent with the expectation from backgrounds. Limits from the combination of all three channels on the Higgs boson production cross section times branching ratio sigma x BR(H --> WW(*) are presented.     

Improved search for a Higgs boson produced in association with Z → l+ l- in pp collisions sqrt[s] = 1.96 TeV

We search for the standard model Higgs boson produced with a Z boson in 4.1 fb(-1) of integrated luminosity collected with the CDF II detector at the Tevatron. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the Z boson to electrons or muons, we set 95% credibility level upper limits on the ZH production cross section multiplied by the H → bb branching ratio. Improved analysis methods enhance signal sensitivity by 20% relative to previous searches. At a Higgs boson mass of 115 GeV/c2 we set a limit of 5.9 times the standard model cross section.     

Light minimal supersymmetric standard model Higgs boson scenario and its test at hadron colliders

We show that, in the minimal supersymmetric standard model, the possibility for the lightest CP-even Higgs boson to be lighter than Z boson (as low as about 60 GeV) is, contrary to the usual belief, not yet excluded by the CERN LEP2 Higgs search nor any direct searches for supersymmetric particles at high energy colliders. The characteristic of the light Higgs boson scenario (LHS) is that the ZZh coupling and the decay branching ratio Br(h/A-->bb) are simultaneously suppressed as a result of generic supersymmetric loop corrections. Consequently, the W(+/-)H(-/+)h coupling has to be large due to the sum rule of Higgs couplings to weak gauge bosons. We discuss the potential of the Fermilab Tevatron and B factories to test the LHS, and show that the associated neutral and charged Higgs boson production process, pp-->H(+/-)h(A), can completely probe the LHS at the CERN Large Hadron Collider.     

Search for a low-mass standard model Higgs boson in the ττ decay channel in pp collisions at sqrt[s]=1.96 TeV

We report on a search for the standard model Higgs boson decaying into pairs of τ leptons in pp collisions produced by the Tevatron at sqrt[s]=1.96 TeV. The analyzed data sample was recorded by the CDFII detector and corresponds to an integrated luminosity of 6.0 fb(-1). The search is performed in the final state with one τ decaying leptonically and the second one identified through its semihadronic decay. Since no significant excess is observed, a 95% credibility level upper limit on the production cross section times branching ratio to the ττ final state is set for hypothetical Higgs boson masses between 100 and 150 GeV/c2. For a Higgs boson of 120 GeV/c2 the observed (expected) limit is 14.6 (15.3) the predicted value.     

Discovering the Higgs bosons of minimal supersymmetry with muons and a bottom quark

We investigate the prospects for the discovery at the CERN Large Hadron Collider (LHC) of a neutral Higgs boson produced with one bottom quark followed by Higgs decay into a muon pair. We work within the framework of the minimal supersymmetric model. The dominant physics background from the production of b mu(+)mu(-), j mu(+)mu(-), j=g,u,d,s,c, and bbW+W- is calculated with realistic acceptance cuts. Promising results are found for the CP-odd pseudoscalar (A0) and the heavier CP-even scalar (H0) Higgs bosons with masses up to 600 GeV. This discovery channel with one energetic bottom quark greatly improves the discovery potential of the LHC beyond the inclusive channel pp-->phi(0)-->mu(+)mu(-)+X.     

Measuring the Higgs boson self-coupling at the Large Hadron Collider

Inclusive standard model Higgs boson pair production and subsequent decay to same-sign dileptons via weak gauge W+/- bosons at the CERN Large Hadron Collider (LHC) has the capability to determine the Higgs boson self-coupling, lambda. The large top quark mass limit is found not to be a good approximation for the signal if one wishes to utilize differential distributions in the analysis. We find that it should be possible at the LHC with design luminosity to establish that the standard model Higgs boson has a nonzero self-coupling and that lambda/lambda(SM) can be restricted to a range of 0-3.7 at 95% confidence level if its mass is between 150 and 200 GeV.     

Search for invisibly decaying Higgs bosons with large decay width using the OPAL detector at LEP

This paper describes a topological search for an invisibly decaying Higgs boson, H, produced via the Bjorken process (e⁺e^-→HZ). The analysis is based on data recorded using the OPAL detector at LEP at centre-of-mass energies from 183 to 209 GeV corresponding to a total integrated luminosity of 629 pb^-1. In the analysis only hadronic decays of the Z boson are considered. A scan over Higgs boson masses from 1 to 120 GeV and decay widths from 1 to 3000 GeV revealed no indication for a signal in the data. From a likelihood ratio of expected signal and standard model background we determine upper limits on cross-section times branching ratio to an invisible final state. For moderate Higgs boson decay widths, these range from about 0.07 pb (M_H=60 GeV) to 0.57 pb (M_H=114 GeV). For decay widths above 200 GeV the upper limits are of the order of 0.15 pb. The results can be interpreted in general scenarios predicting a large invisible decay width of the Higgs boson. As an example we interpret the results in the so-called stealthy Higgs scenario. The limits from this analysis exclude a large part of the parameter range of this scenario experimentally accessible at LEP 2.     

Jet substructure as a new Higgs-search channel at the Large Hadron Collider

It is widely considered that, for Higgs boson searches at the CERN Large Hadron Colider, WH and ZH production where the Higgs boson decays to bb are poor search channels due to large backgrounds. We show that at high transverse momenta, employing state-of-the-art jet reconstruction and decomposition techniques, these processes can be recovered as promising search channels for the standard model Higgs boson around 120 GeV in mass.     

Higgs–photon resonances

We study models that produce a Higgs boson plus photon (\(h^0\gamma \)) resonance at the LHC. When the resonance is a \(Z'\) boson, decays to \(h^0\gamma \) occur at one loop. If the \(Z'\) boson couples at tree level to quarks, then the \(h^0\gamma \) branching fraction is typically of order \(10^{-5}\) or smaller. Nevertheless, there are models that would allow the observation of \(Z'\rightarrow \,h^0\gamma \) at \(\sqrt{s}=13\) TeV with a cross section times branching fraction larger than 1 fb for a \(Z'\) mass in the 200–450 GeV range, and larger than 0.1 fb for a mass up to 800 GeV. The one-loop decay of the \(Z'\) into lepton pairs competes with \(h^0\gamma \), even if the \(Z'\) couplings to leptons vanish at tree level. We also present a model in which a \(Z'\) boson decays into a Higgs boson and a pair of collimated photons, mimicking an \(h^0\gamma \) resonance. In this model, the \(h^0\gamma \) resonance search would be the discovery mode for a \(Z'\) as heavy as 2 TeV. When the resonance is a scalar, although decay to \(h^0\gamma \) is forbidden by angular momentum conservation, the \(h^0\) plus collimated photons channel is allowed. We comment on prospects of observing an \(h^0\gamma \) resonance through different Higgs decays, on constraints from related searches, and on models where \(h^0\) is replaced by a nonstandard Higgs boson.     

Higgs bosons in the Next-to-Minimal Supersymmetric Standard Model at the LHC

We review possible properties of Higgs bosons in the NMSSM, which allow to discriminate this model from the MSSM: masses of mostly Standard-Model-like Higgs bosons at or above 140 GeV, or enhanced branching fractions into two photons, or Higgs-to-Higgs decays. In the case of a Standard-Model-like Higgs boson above 140 GeV, it is necessarily accompanied by a lighter state with a large gauge singlet component. Examples for such scenarios are presented. Available studies on Higgs-to-Higgs decays are discussed according to the various Higgs production modes, light Higgs masses and decay channels.     

Search for a very light CP-odd Higgs boson in top quark decays from pp collisions at sqrt(s)]=1.96 TeV

We present the results of a search for a very light CP-odd Higgs boson a(1)(0) originating from top quark decays t → H(±)b → W(±(*)) a(1)(0)b, and subsequently decaying into τ+ τ-. Using a data sample corresponding to an integrated luminosity of 2.7 fb(-1) collected by the CDF II detector in pp collisions at 1.96 TeV, we perform a search for events containing a lepton, three or more jets, and an additional isolated track with transverse momentum in the range 3 to 20 GeV/c. Observed events are consistent with background sources, and 95% C.L. limits are set on the branching ratio of t → H(±)b for various masses of H(±) and a(1)(0).     

Higgs boson production and decay in little Higgs models with T-parity

We study Higgs boson production and decay in a certain class of little Higgs models with T-parity in which some T-parity partners of the Standard Model (SM) fermions gain their masses through Yukawa-type couplings. We find that the Higgs boson production cross section of a 120 GeV Higgs boson at the CERN LHC via gg fusion process at one-loop level could be reduced by about 45%, 35% and 20%, as compared to its SM prediction, for a relatively low new particle mass scale f=600, 700 and 1000 GeV, respectively. On the other hand, the weak boson fusion cross section is close to the SM value. Furthermore, the Higgs boson decay branching ratio into di-photon mode can be enhanced by about 35% in small Higgs mass region in certain case, for the total decay width of Higgs boson in the little Higgs model is always smaller than that in the SM.     

With four standard model families, the LHC could discover the Higgs boson with a few fb-1

The existence of a 4th SM family would produce a large enhancement of the gluon fusion channel of Higgs boson production at hadron colliders. In this case, the SM Higgs boson could be seen at the CERN Large Hadron Collider (LHC) via the golden mode () with an integral luminosity of only a few fb^-1. Received: 26 February 2002 / Published online: 18 October 2002     

Radiative B meson decays into kpigamma and kpipigamma final states

We report observations of radiative B meson decays into the K+pi(-)gamma and K+pi(-)pi(+)gamma final states. In the B0-->K+pi(-)gamma channel, we present evidence for decays via an intermediate tensor meson state with a branching fraction of B(B0-->K(*)(2)(1430)(0)gamma)=[1.3+/-0.5(stat)+/-0.1(syst)]x10(-5). We measure the branching fraction B(B+-->K+pi(-)pi(+)gamma)=[2.4+/-0.5(stat) +0.4-0.2(syst)]x10(-5), in which the B+-->K(*0)pi(+)gamma and B+-->K+rho(0)gamma channels dominate. The analysis is based on a data set of 29.4 fb(-1) recorded by the Belle experiment at the KEKB collider.     

Determining the CP parity of Higgs bosons via their tau decay channels at the Large Hadron Collider

If neutral Higgs bosons are discovered at the CERN Large Hadron Collider (LHC), then an important subsequent issue will be the investigation of their CP nature. Higgs boson decays into tau lepton pairs are particularly suited in this respect. By analyzing the three charged pion decay modes of the tau leptons and taking expected measurement uncertainties at the LHC into account, we show that the CP properties of a Higgs boson can be pinned down with appropriately chosen observables, provided that sufficiently large event numbers will eventually be available.     

Search for the standard model Higgs boson in the decay channel H→ZZ→4ℓ in pp collisions at √s=7 TeV

A search for a Higgs boson in the four-lepton decay channel H→ZZ, with each Z boson decaying to an electron or muon pair, is reported. The search covers Higgs boson mass hypotheses in the range of 110100 GeV (with 13 below 160 GeV), while 67.1±6.0 (9.5±1.3) events are expected from background. The four-lepton mass distribution is consistent with the expectation of standard model background production of ZZ pairs. Upper limits at 95% confidence level exclude the standard model Higgs boson in the ranges of 134-158 GeV, 180-305 GeV, and 340-465 GeV. Small excesses of events are observed around masses of 119, 126, and 320 GeV, making the observed limits weaker than expected in the absence of a signal.     

Six-quark decays of the Higgs boson in supersymmetry with R-parity violation

Both electroweak precision measurements and simple supersymmetric extensions of the standard model prefer a mass of the Higgs boson less than the experimental lower limit (on a standard-model-like Higgs boson) of 114 GeV. We show that supersymmetric models with R parity violation and baryon-number violation have a significant range of parameter space in which the Higgs boson dominantly decays to six jets. These decays are much more weakly constrained by current CERN LEP analyses and would allow for a Higgs boson mass near that of the Z. In general, lighter scalar quark and other superpartner masses are allowed. The Higgs boson would potentially be discovered at hadron colliders via the appearance of new displaced vertices.     

Search for a Higgs boson in the diphoton final state in pp collisions at sqrt[s]=1.96 TeV

A search for a narrow Higgs boson resonance in the diphoton mass spectrum is presented based on data corresponding to 7.0 fb{-1} of integrated luminosity from pp collisions at sqrt[s]=1.96 TeV collected by the CDF experiment. No evidence of such a resonance is observed, and upper limits are set on the cross section times branching ratio of the resonant state as a function of Higgs boson mass. The limits are interpreted in the context of the standard model and one fermiophobic benchmark model where the data exclude fermiophobic Higgs bosons with masses below 114 GeV/c{2} at a 95% Bayesian credibility level.     

Search for neutral minimal supersymmetric standard model Higgs bosons decaying to tau pairs produced in association with b quarks in pp collisions at √s = 1.96 TeV

We report results from a search for neutral Higgs bosons produced in association with b quarks using data recorded by the D0 experiment at the Fermilab Tevatron Collider and corresponding to an integrated luminosity of 7.3 fb(-1). This production mode can be enhanced in several extensions of the standard model (SM) such as in its minimal supersymmetric extension (MSSM) at high tanβ. We search for Higgs bosons decaying to tau pairs with one tau decaying to a muon and neutrinos and the other to hadrons. The data are found to be consistent with SM expectations, and we set upper limits on the cross section times branching ratio in the Higgs boson mass range from 90 to 320 GeV/c(2). We interpret our result in the MSSM parameter space, excluding tanβ values down to 25 for Higgs boson masses below 170 GeV/c(2).