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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
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DOE OSTI2011

Search for the Higgs Boson in the H{yields}WW{yields}l{nu}jj Decay Channel in pp Collisions at {radical}(s)=7 TeV with the ATLAS Detector

A search for a Higgs boson has been performed in the H{yields}WW{yields}l{nu}jj channel in 1.04 fb{sup -1} of pp collision data at {radical}(s)=7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No significant excess of events is observed over the expected background and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 240 GeV<m{sub H}<600 GeV. The best sensitivity is reached for m{sub H}=400 GeV, where the 95% confidence level upper bound on the cross section for H{yields}WW production is 3.1 pb, or 2.7 times the standard model prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Higgs phenomenology in warped extra dimensions with a fourth generation

We study a warped extra-dimension scenario where the standard model fields lie in the bulk, with the addition of a fourth family of fermions. We concentrate on the flavor structure of the Higgs couplings with fermions in the flavor anarchy ansatz. Even without a fourth family, these couplings will be generically misaligned with respect to the standard model fermion mass matrices. The presence of the fourth family typically enhances the misalignment effects and we show that one should expect them to be highly nonsymmetrical in the (34) intergenerational mixing. The radiative corrections from the new fermions and their flavor-violating couplings to the Higgs affect negligibly known experimental precision measurements such as the oblique parameters and Z{yields}bb or Z{yields}{mu}{sup +}{mu}{sup -}. On the other hand, {Delta}F=1, 2 processes, mediated by tree-level Higgs exchange, as well as radiative corrections to b{yields}s{gamma} and {mu}{yields}e{gamma} put some generic pressure on the allowed size of the flavor-violating couplings. But more importantly, these couplings will alter the Higgs decay patterns as well as those of the new fermions, and produce very interesting new signals associated to Higgs phenomenology in high energy colliders. These signals might become very important indirect signals for these type of models as they would be present even when the KK mass scale is high and no heavy KK particle is discovered.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Production of charged Higgs bosons in a 3-3-1 model at the CERN LHC

We perform a study of the charged Higgs production from an SU(3){sub C} x SU(3){sub L} x U(1){sub X} model with right-handed neutrinos, postulating a custodial symmetry which reduces the number of free parameters in the scalar potential. We compute the cross sections for charged scalars for typical and new production modes. One of the new SU(3){sub L} neutral gauge bosons, Z', affects some production cross sections distinguishing the model from other standard model extensions like, for example, the minimal supersymmetric standard model and general two-Higgs doublets models. The interplay between the Higgs sector of the model and that Z' gauge boson enhances substantially all the production rates of the lightest charged Higgs boson, H{sub 1}{sup {+-}}, at hadron colliders compared to the MSSM. We found that a large portion of the parameters space can be probed at the LHC running at 14 TeV center-of-mass energy in the associated pp{yields}W{sup {+-}H}{sub 1}{sup {+-}+}X production channel in the low luminosity run stage of the experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Associated Higgs-W-Boson Production at Hadron Colliders: A Fully Exclusive QCD Calculation at NNLO

We consider QCD radiative corrections to standard model Higgs-boson production in association with a W boson in hadron collisions. We present a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform this NNLO computation, we use a recently proposed version of the subtraction formalism. Our calculation includes finite-width effects, the leptonic decay of the W boson with its spin correlations, and the decay of the Higgs boson into a bb pair. We present selected numerical results at the Tevatron and the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Search for a Standard Model Higgs Boson with a Dilepton and Missing Energy Signature

The subject of this thesis is the search for a standard model Higgs boson decaying to a pair of W bosons that in turn decay leptonically, H → W + W - → $\bar{ℓ}$vℓ$\bar{v}$. This search is performed considering events produced in p$\bar{p}$ collisions at √s = 1.96 TeV, where two oppositely charged lepton candidates (e + e - , e ± μ ± , or μ + μ} - ), and missing transverse energy, have been reconstructed. The data were collected with the D0 detector at the Fermilab Tevatron collider, and are tested against the standard model predictions computed for a Higgs boson with mass in the range 115-200 GeV. No excess of events over background is observed, and limits on Standard Model Higgs boson production are determined. An interpretation of these limits within the hypothesis of a fourth-generation extension to the standard model is also given. The overall analysis scheme is the same for the three dilepton pairs being considered (e + e - , e ± μ ± , or μ + μ - ); this thesis, however, describes in detail the study of the dimuon final state.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Z{gamma}{gamma} production with leptonic decays and triple photon production at next-to-leading order QCD

We present a calculation of the O({alpha}{sub s}) QCD corrections to the production of a Z boson in association with two photons and to triple-photon production at hadron colliders. All final-state photons are taken as real. For the Z boson, we consider the decays both into charged leptons and into neutrinos including all off-shell effects. Numerical results are obtained via a Monte Carlo program based on the structure of the VBFNLO program package. This allows us to implement general cuts and distributions of the final-state particles. We find that the next-to-leading order QCD corrections are sizable and significantly exceed the expectations from a scale variation of the leading-order result. In addition, differential distributions of important observables change considerably. The prediction of two-photon-associated Z production with Z decays into neutrinos from the charged-lepton rate works well, once we use an additional cut on the invariant mass of the charged-lepton pair.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Gauged L{sub {mu}}-L{sub {tau}} symmetry at the electroweak scale

The extension of the standard model by a spontaneously broken abelian gauge group based on the L{sub {mu}}-L{sub {tau}} lepton number can resolve the long-standing discrepancy between experimental and theoretical values for the magnetic moment of the muon. It furthermore naturally generates {mu}-{tau} symmetric lepton mixing, introduces neutrino nonstandard interactions, and the associated gauge boson Z' serves as a mediator to the right-handed neutrino sector. A detailed fit to electroweak data is performed to identify the allowed values for the mass of Z' and its mixing with the standard model Z. An economical new scalar sector is constructed that spontaneously breaks L{sub {mu}}-L{sub {tau}} and leads to experimental consequences such as lepton flavor violation and collider signatures. Furthermore we discuss the nonabelian extension to an SU(2){sup '}, particularly the neutrino sector.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Next-to-leading order QCD predictions for the signal of dark matter and photon associated production at the LHC

We study the potential of the LHC to discover the signal of dark matter associated production with a photon induced by a dimension six effective operator, including next-to-leading order QCD corrections. We investigate the main backgrounds from the standard model, i.e. Z boson and a photon associated production with invisible decay of Z boson, and Z boson and a jet production with the jet misidentified as a photon. We find that the p{sub T}{sup {gamma}} distributions of the backgrounds decrease faster than that of the signal with increasing of the transverse momentum of the photon. The {eta}{sup {gamma}} distributions of the backgrounds are almost flat in the full range of {eta}{sup {gamma}}. In contrast, the signal lies mainly in the central region of {eta}{sup {gamma}}. These characteristics may help to select the events in experiments. We show that in the parameter space allowed by the relic abundance constraint, which we have calculated at the next-to-leading-order QCD level, the LHC with {radical}(S)=7 TeV may discover this signal at the 5{sigma} level after collecting an integrated luminosity of 1 fb{sup -1}. On the other hand, if this signal is not observed at the LHC, we can set a lower limit on the new physics scale at the 3{sigma} level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Top quark forward-backward asymmetry, flavor-changing neutral-current decays, and like-sign pair production as a joint probe of new physics

The anomaly of the top quark forward-backward asymmetry A{sub FB}{sup t} observed at the Tevatron can be explained by the t-channel exchange of a neutral gauge boson (Z{sup '}) which has sizable flavor-changing coupling for top and up quarks. This gauge boson can also induce the top quark flavor-changing neutral-current (FCNC) decays and the like-sign top pair production at the LHC. In this work, we focus on two models which predict such a Z', namely, the left-right model and the U(1){sub X} model, to investigate the correlated effects on A{sub FB}{sup t}, the FCNC decays t{yields}uV (V=g, Z, {gamma}) and the like-sign top pair production at the LHC. We also pay special attention to the most recently measured A{sub FB}{sup t} in the large top pair invariant mass region. We find that under the current experimental constraints both models can alleviate the deviation of A{sub FB}{sup t} and, meanwhile, enhance the like-sign top pair production to the detectable level of the LHC. We also find that the two models give different predictions for the observables and their correlations, and thus they may even be distinguished by jointly studying these top quark observables.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗