Higgs physics at LHC

The large hadron collider (LHC) and its detectors, ATLAS and CMS, are being built to study TeV scale physics, and to fully understand the electroweak symmetry breaking mechanism. The Monte-Carlo simulation results for the standard model and minimal super symmetric standard model Higgs boson searches and parameter measurements are discussed. Emphasis is placed on recent investigations of Higgs produced in association with top quarks and in vector boson fusion channels. These results indicate that Higgs sector can be explored in many channels within a couple of years of LHC operation, i.e.,L = 30 fb⁻¹. Complete coverage including measurements of Higgs parameters can be carried out with full LHC program.     

Distinguishing a SM-like MSSM Higgs boson from SM Higgs boson at muon collider

We explore the possibility of distinguishing the SM-like MSSM Higgs boson from the SM Higgs boson via Higgs boson pair production at future muon collider. We study the behavior of the production cross-section in SM and MSSM with Higgs boson mass for various MSSM parameters tan β and m _A . We observe that at fixed CM energy, in the SM, the total cross-section increases with the increase in Higgs boson mass whereas this trend is reversed for the MSSM. The changes that occur for the MSSM in comparison to the SM predictions are quantified in terms of the relative percentage deviation in cross-section. The observed deviations in cross-section for different choices of Higgs boson masses suggest that the measurements of the cross-section could possibly distinguish the SM-like MSSM Higgs boson from the SM Higgs boson.      

The standard model Higgs search at the large hadron collider

The experiments at the large hadron collider (LHC) will probe for Higgs boson in the mass range between the lower bound on the Higgs mass set by the experiments at the large electron positron collider (LEP) and the unitarity bound (∼1 TeV). Strategies are being developed to look for signatures of Higgs boson and measure its properties. In this paper results from full detector simulation-based studies on Higgs discovery from both ATLAS and CMS experiments at the LHC will be presented. Results of simulation studies on Higgs coupling measurement at LHC will be discussed. on behalf of the CMS and the ATLAS Collaborations     

Neutral Higgs bosons in the standard model and in the minimal supersymmetric model: Searches at LEP

During the twelve years of operation of thee ⁺ e ⁻ collider LEP, the associated collaborations, ALEPH, DELPHI, L3 and OPAL, have extensively searched for Higgs bosons over a broad range of masses. We present the final results from LEP for the standard model Higgs boson which are obtained from a statistical combination of the data from the four experiments. We also present preliminary combined results for neutral Higgs bosons in the minimal supersymmetric model (MSSM) where the Higgs sector is assumed to be CP invariant. Finally, we discuss an alternative MSSM scenario including CP violation in the Higgs sector.     

Anomalous <Emphasis Type="Italic">VVH</Emphasis> interactions at a linear collider

We examine, in a model independent way, the sensitivity of a linear collider to the couplings of a light Higgs boson to a pair of gauge bosons, including the possibility of CP violation. We construct several observables that probe the various possible anomalous couplings. For an intermediate mass Higgs, a collider operating at a center of mass energy of 500 GeV and with an integrated luminosity of 500 fb⁻¹ is shown to be able to constrain the ZZH vertex at the few per cent level, with even higher sensitivity for some of the couplings. However, lack of sufficient number of observables as well as contamination from the ZZH vertex limits the precision to which anomalous part of the WWH coupling can be probed.      

Littlest Higgs model and <Emphasis Type="Italic">W</Emphasis> pair production at international linear collider

Among the viable alternatives to the standard Higgs mechanism is the recently proposed Little Higgs model. The advantage here is that the model has an elementary light neutral scalar particle, which arises dynamically as against its ad hoc introduction in the standard model. The model also avoids hierarchy problem. We have investigated the W pair production at ILC to study the littlest Higgs model using different observables. Specifically, polarization fraction of W boson is expected to be measured very accurately at ILC. We use this to put limit on the scale parameter, f, in the model.      

Higgs self-coupling in the fusion channel at the international linear collider

We investigate the Higgs pair production process at the international linear collider (ILC), focusing on the measurement of the trilinear self-coupling of the Higgs boson in the fusion channel. The sensitivity of this measurement is discussed in the Higgs mass range 140–200 GeV at a center-of-mass energy between 1 TeV and 1.5 TeV.      

Discovery of the Higgs boson by the ATLAS and CMS experiments at the LHC

The Standard Model (SM) Higgs boson was predicted by theorists in the 1960s during the development of the electroweak theory. Prior to the startup of the CERN Large Hadron Collider (LHC), experimental searches found no evidence of the Higgs boson. In July 2012, the ATLAS and CMS experiments at the LHC reported the discovery of a new boson in their searches for the SM Higgs boson. Subsequent experimental studies have revealed the spin-0 nature of this new boson and found its couplings to SM particles consistent to those of a Higgs boson. These measurements confirmed the newly discovered boson is indeed a Higgs boson. More measurements will be performed to compare the properties of the Higgs boson with the SM predictions.     

Large hadron collider physics program: Compact muon solenoid experiment

The LHC physics program at CERN addresses some of the fundamental issues in particle physics and CMS experiment would concentrate on them. The CMS detector is designed for the search of Standard Model Higgs boson in the whole possible mass range. Also it will be sensitive to Higgs bosons in the minimal supersymmetric model and well adapted to searches for SUSY particles, new massive vector bosons, CP-violation in B-system, search for subtructure of quarks and leptons, etc. In the LHC heavy ion collisions the energy density would be well above the threshold for the possible formation of quark-gluon plasma.     

Recent results from LEP

Recent results from the LEP collider at CERN are presented: on the identification of e ⁺ e ⁻ → W ⁺ W ⁻ and the determination of the W mass and width and limits on its anomalous couplings; the search for the Standard Model and non-minimal Higgs; search for SUSY and other new particles. Fits to all electroweak data leading to predictions of the Higgs mass within the Standard Model are presented.     

Associated ZH and WH Production in Left-Right Twin Higgs Model at LHC

At the CERN large hadron collider (LHC), production of the Higgs boson in association with Z or W bosons provides a dramatic experimental signal for detecting the standard model (SM) Higgs boson. In this paper, we consider the contributions of the left-right twin Higgs (LRTH) model to the processes q\bar{q}→Z(W)H. Our numerical results show that, in the favorable parameter spaces, the cross sections deviate distinctly from the predictions
of the SM. The possible signals of the LRTH model can be detected via these processes at the LHC experiments.     

Triviality bound on lightest Higgs mass in next to minimal supersymmetric model

We study the implication of triviality on Higgs sector in next to minimal supersymmetric model (NMSSM) using variational field theory. It is shown that the mass of the lightest Higgs boson in NMSSM has an upper bound ∼10M _W which is of the same order as that in the standard model.     

Probing CP-violating Higgs contributions in γγ → f$$ \bar f $$

We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson ϕ in γγ → f , f = τ/t, from that of the QED continuum. This can help in getting information on the γγϕ coupling in case ϕ is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case ϕ has indeterminate CP. Furthermore, we take the MSSM with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters.      

The road towards the international linear collider: Higgs,top/quantum chromodynamics,loops

The international linear e ⁺ e ⁻ collider (ILC) could go into operation in the second half of the upcoming decade. Experimental analyses and theory calculations for the physics at the ILC are currently performed. We review recent progress, as presented at the LCWS06 in Bangalore, India, in the fields of Higgs boson physics and top/QCD. Also the area of loop calculations, necessary to achieve the required theory precision, is included.      

Study of charged and neutral minimal supersymmetric standard model Higgs boson decays and measurement of tan <Emphasis Type="Italic">β</Emphasis> at the compact linear collider

The minimal supersymmetric extension of the standard model (MSSM) predicts the existence of new charged and neutral Higgs bosons. The pair creation of these new particles at the multi-TeV e ⁺ e ⁻ compact linear collider (CLIC), followed by decays into standard model particles, were simulated along with the corresponding background. High-energy beam-beam effects such as ISR, beamstrahlung and hadronic background were included. We have investigated the possibility of using the ratio between the number of events found in various decay channels to determine the MSSM parameter tan β and we have derived the corresponding statistical error from the uncertainties on the measured cross-sections and Higgs boson masses.      

Charged and neutral minimal supersymmetric standard model Higgs boson decays and measurement of tan <Emphasis Type="Italic">β</Emphasis> at the compact linear collider

The minimal supersymmetric extension of the standard model (MSSM) predicts the existence of new charged and neutral Higgs bosons. The pair creation of these new particles at the multi-TeV e ⁺ e ⁻ compact linear collider (CLIC), followed by decays into standard model particles, were simulated along with the corresponding background. High-energy beam-beam effects such as ISR, beamstrahlung and hadronic background were included. We have investigated the possibility of using the ratio between the number of events found in various decay channels to determine the MSSM parameter tan β and we have derived the corresponding statistical error from the uncertainties on the measured cross-sections and Higgs boson masses.      

The Higgs boson discovery and measurements

The discovery of the Higgs boson at a mass around 125 GeV by the ATLAS and CMS experiments at the LHC collider in 2012 establishes a new landscape in high-energy physics. The analysis of the full data sample collected with pp collisions at centre-of-mass energies of 7 and 8 TeV has allowed for considerable progress since the discovery. A review of the latest results is presented.     

Z–Z' mixing effects in W boson pair production processes at hadron and lepton high-energy colliders

Potential possibilities to detect the effects of Z–Z' mixing in the W-pair production process in proton-proton and electron–positron collisions at the Large Hadron Collider (LHC) and International Linear Collider (ILC) have been studied. It has been established that the processes of W boson pair production are very sensitive to the angle of Z–Z' mixing and their measurements in current and future experiments will make it possible to improve modern restrictions on the angle of Z–Z' mixing in the models with extended gauge sector. At a nominal energy of 14 TeV and an integral luminosity of 100 fb^–1, the LHC collider can offer much more precise information on the parameter of Z–Z' mixing and the mass M ₂ than can be obtained using the ILC leptonic collider (0.5 TeV).     

Photon pairs: Quantum chromodynamics continuum and the Higgs boson

A new QCD calculation is summarized for the transverse momentum distribution of photon pairs produced by QCD subprocesses, including all-orders soft-gluon resummation valid at next-to-next-to-leading logarithmic accuracy. Resummation is needed to obtain reliable predictions in the range of transverse momentum where the cross-section is the largest. Results are compared with data from the Fermilab Tevatron and predictions are made for the large hadron collider. The QCD continuum is shown to have a softer spectrum than the Higgs boson signal at the LHC.      

SUSY effects in Higgs production at high energy e+e- colliders

Considering the constraints from collider experiments and dark matter detection, we investigate the SUSY effects in the Higgs production channels e⁺e^-→Zh at an e⁺e^- collider with a center-of-mass energy above 240 GeV and γγ→h→bb at a photon collider with a center-of-mass energy above 125 GeV. In the parameter space allowed by current experiments, we find that the SUSY corrections to e⁺e^-→Zh can reach a few percent and the production rate of γγ→h→bb can be enhanced by a factor of 1.2 over the SM prediction. We also calculate the exotic Higgs production e⁺e^-→Zh₁ in the next-to-minimal supersymmetric model (NMSSM) (h is the SM-like Higgs, h₁ is the CP-even Higgs bosons which can be much lighter than h). We find that at a 250 GeV e⁺e^- collider the production rates of e⁺e^-→Zh₁ can reach 60 fb.