W-exchange dominance in neutral B-meson decay

Tests of W-exchange dominance in neutral B-meson decay are developed from the isospin and SU(3) properties of the final state. For B⁰ (d), it is shown that the decay rates into (D⁺ plus anything) and into (F⁺ plus anything) are always equal to one another and never more than $\text{3}\text{2}$ times the rate for (D⁰ plus anything). A similar analysis is applied to B⁰(s), and it is suggested that any of the four possibilities {;ψ, η_c}+(φ, η′) would make a good signal for this meson.     

Higgs boson bremsstrahlung in top quark decay

In top quark decay a neutral Higgs boson may be emitted in bremsstrahlung from the top quark or from the W-boson. We evaluate the branching fraction for this hitherto overlooked t→H⁰bW⁺ decay mode, where the W⁺ can be virtual or real. It has the standard model values of 0.02%, 0.2%, 0.8% for m_t=50, 100, 200 GeVand m_H=10 GeV.     

Search for a neutral Higgs boson decaying to a W boson pair in pp collisions at square root of s = 1.96 TeV

We present the results of a search for standard model Higgs boson production with decay to WW*, identified through the leptonic final states e+ e- nu nu,+/-mu -/+nu nu and mu+ mu- nu nu. This search uses 360 pb -1 of data collected from pp collisions at square root of s =1.96 TeV by the upgraded Collider Detector at Fermilab (CDF II). We observe no signal excess and set 95% confidence level upper limits on the production cross section times branching ratio for the Higgs boson to WW* or any new scalar particle with similar decay products. These upper limits range from 5.5 to 3.2 pb for Higgs boson masses between 120 and 200 GeV/c2.     

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.     

Search for a lighter Higgs boson in the Next-to-Minimal Supersymmetric Standard Model

Following the discovery of the Higgs boson with a mass of approximately 125 Ge V at the LHC, many studies have been performed from both the theoretical and experimental viewpoints to search for a new Higgs Boson that is lighter than 125 Ge V. We explore the possibility of constraining a lighter neutral scalar Higgs boson h_1 and a lighter pseudo-scalar Higgs boson a_1 in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson h_2 to be the one observed at the LHC after applying the phenomenological constraints and those from experimental measurements. Such lighter particles are not yet completely excluded by the latest results of the search for a lighter Higgs boson in the diphoton decay channel from LHC data. Our results show that some new constraints on the Next-to-Minimal Supersymmetric Standard Model could be obtained for a lighter scalar Higgs boson at the LHC if such a search is performed by experimental collaborations and more data. The potentials of discovery for other interesting decay channels of such a lighter neutral scalar or pseudo-scalar particle are also discussed.     

CP asymmetries in top quark pair production and decay: contributions from neutral Higgs boson and gluino exchange

Zeitschrift für Physik C Particles and Fields - For $$e^ + e^ - \to \bar tt$$ with subsequent semileptonic $$\bar t$$ and nonleptonic $$\bar t$$ decay and vice versa we investigate a few...     

SUSY background to neutral MSSM Higgs boson searches

Within the Minimal Supersymmetric Standard Model (MSSM) the production and decay of superpartners can give rise to backgrounds for Higgs boson searches. Here MSSM background processes to the vector boson fusion channel with the Higgs boson decaying into two tau leptons or two W-bosons are investigated, giving rise to dilepton plus missing transverse momentum signals of the Higgs boson. Starting from a scenario with relatively small masses of the supersymmetric (SUSY) particles, with concomitant large cross section of the background processes, one obtains a first conservative estimate of the background. Light chargino pair production plus two jets, lightest and next-to-lightest neutralino production plus two jets as well as slepton pair production plus two jets are identified as important contributions to the irreducible SUSY background. Light chargino and next-to-lightest neutralino production plus two jets and next-to-lightest neutralino pair production plus two jets give rise to reducible backgrounds, which can be larger than the irreducible ones in some scenarios. The relevant distributions are shown and additional cuts for MSSM background reduction are discussed. Extrapolation to larger squark masses is performed and shows that MSSM backgrounds are quite small for squark masses at the current exclusion limits.     

Search for a fermiophobic and standard model Higgs boson in diphoton final states

We present a search for the standard model Higgs boson and a fermiophobic Higgs boson in the diphoton final states based on 8.2 fb(-1) of pp collisions at sqrt[s]=1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. No excess of data above background predictions is observed and upper limits at the 95% C.L. on the cross section multiplied by the branching fraction are set which are the most restrictive to date. A fermiophobic Higgs boson with a mass below 112.9 GeV is excluded at the 95% C.L.     

Search for a Higgs boson decaying into two photons in the CMS detector

A search for a Higgs boson decaying into two photons in pp collisions at the LHC at a centre-of-mass energy of 7 TeV is presented. The analysis is performed on a dataset corresponding to 1.66 fb^?1 of data recorded in 2011 by the CMS experiment. Limits are set on the cross-section of a Standard Model Higgs boson decaying into two photons, and on the cross-section of a fermiophobic Higgs boson decaying into two photons.     

Search for invisibly decaying Higgs boson at Large Hadron Collider

In several scenarios of Beyond Standard Model physics, the invisible decay mode of the Higgs boson is an interesting possibility. The search strategy for an invisible Higgs boson at the Large Hadron Collider (LHC), using weak boson fusion process, has been studied in detail, by taking into account all possible backgrounds. Realistic simulations have been used in the context of CMS experiment to devise a set of event selection criteria which eventually enhances the signal contribution compared to the background processes in characteristic distributions. In cut-based analysis, multi-jet background is found to overwhelm the signal in the finally selected sample. With an integrated luminosity of 10 fb⁻¹, an upper limit of 36% on the branching ratio can be obtained for Higgs boson with a mass of 120 GeV/c² for LHC energy of 14 TeV. Since the analysis essentially depends on the background estimation, detailed studies have been done to determine the background rates from real data.