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.     

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.     

Production of Neutral Top-Pion Associated with a Gauge Boson at LHC

In this paper, we study the production of the neutral top-pion (Π⁰_t) associated with a gauge boson at the LHC, i.e. pp→Π⁰_tV(V=g,W,Z,γ). The cross section of pp→Π⁰_tg is at the level of 10² pb in the most parameter space. Such a process with the flavor-changing decay mode Π⁰_t→ tc might provide viable signatures to detect Π⁰_t at the LHC. The cross sections of other processes pp→Π⁰_tW(Z,γ) are too small to detect Π⁰_t, which open a window to distinguish the Higgs boson in the SM or MSSM from Π⁰_t.     

Differentiating the Higgs boson from the dilaton and radion at Hadron colliders

A number of candidate theories beyond the standard model (SM) predict new scalar bosons below the TeV region. Among these, the radion, which is predicted in the Randall-Sundrum model, and the dilaton, which is predicted by the walking technicolor theory, have very similar couplings to those of the SM Higgs boson, and it is very difficult to differentiate these three spin-0 particles in the expected signals of the Higgs boson at the LHC and Tevatron. We demonstrate that the observation of the ratio σ(γγ)/σ(WW) gives a simple and decisive way to differentiate these, independent of the values of model parameters, the vacuum expectation values of the radion, and dilaton fields.     

Neutral Higgs Boson Pair Production in Standard Model with the Fourth Generation Quarks at LHC

We investigated the neutral Higgs boson pair production at the CERN Large Hadron Collider (LHC) in the SM with four families. We found that the gluon-gluon fusion mode is the most dominant one in producing neutral Higgs boson pair at the LHC, and it can be used to probe the trilinear Higgs coupling. If the heavy quarks of the fourth generation really exist within the SM, they can manifest their effect on the cross section of the Higgs pair production process at the LHC. Our numerical results show that there will be 2×10⁴ neutral Higgs boson pair production events per year if the next generation heavy quarks really exist, while there will be only 2×10³ events produced per year if there are only three families in the SM.     

Pair production of the Elementary Goldstone Higgs boson at the LHC

The Elementary Goldstone Higgs(EGH) model is a perturbative extension of the standard model(SM),which identifies the EGH boson as the observed Higgs boson. In this paper, we study pair production of the EGH boson via gluon fusion at the LHC and find that the resonant contribution of the heavy scalar is very small and the SM-like triangle diagram contribution is strongly suppressed. The total production cross section mainly comes from the box diagram contribution and its value can be significantly enhanced with respect to the SM prediction.     

Higgs physics at CMS

This article reviews recent measurements of the properties of the standard model (SM) Higgs boson using data recorded with the CMS detector at the LHC: its mass, width and couplings to other SM particles. We also summarise highlights from searches for new physical phenomena in the Higgs sector as they are proposed in many extensions of the SM: flavour violating and invisible decay modes, resonances decaying into Higgs bosons and searches for additional Higgs bosons.     

Distinguishing the higgs boson from the dilaton at the large hadron collider

It is likely that the LHC will observe a color- and charge-neutral scalar whose decays are consistent with those of the standard model (SM) Higgs boson. The Higgs interpretation of such a discovery is not the only possibility. For example, electroweak symmetry breaking could be triggered by a spontaneously broken, nearly conformal sector. The spectrum of states at the electroweak scale would then contain a narrow scalar resonance, the pseudo-Goldstone boson of conformal symmetry breaking, with Higgs-boson-like properties. If the conformal sector is strongly coupled, this pseudodilaton may be the only new state accessible at high energy colliders. We discuss the prospects for distinguishing this mode from a minimal Higgs boson at the LHC and ILC. The main discriminants between the two scenarios are (i) cubic self-interactions and (ii) a potential enhancement of couplings to massless SM gauge bosons.     

Study of CEPC performance with different collision energies and geometric layouts

The Circular Electron-Positron Collider(CEPC) is one of the largest projects planned for high energy physics in China.It would serve first as a Higgs factory and then upgrade to a hadron collider.In this paper we give the 50 km and 100 km design for both single ring and double ring schemes,including Z boson,W boson and Higgs boson,by using an optimized method.Also,we give the potential of CEPC running at the Z and W poles.We analyse the relationship of luminosity with circumference and filling factor,which gives a way to evaluate the choice of geometry,and compare the nominal performances of CEPC-SPPC,LHC and FCC.     

NMSSM Higgs benchmarks near 125 GeV

The recent LHC indications of a SM-like Higgs boson near 125 GeV are consistent not only with the Standard Model (SM) but also with Supersymmetry (SUSY). However naturalness arguments disfavour the Minimal Supersymmetric Standard Model (MSSM). We consider the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with a SM-like Higgs boson near 125 GeV involving relatively light stops and gluinos below 1 TeV in order to satisfy naturalness requirements. We are careful to ensure that the chosen values of couplings do not become non-perturbative below the grand unification (GUT) scale, although we also examine how these limits may be extended by the addition of extra matter to the NMSSM at the two-loop level. We then propose four sets of benchmark points corresponding to the SM-like Higgs boson being the lightest or the second lightest Higgs state in the NMSSM or the NMSSM-with-extra-matter. With the aid of these benchmark points we discuss how the NMSSM Higgs boson near 125 GeV may be distinguished from the SM Higgs boson in future LHC searches.     

Implications of the Higgs boson discovery

With the discovery of the Higgs boson by the LHC in 2012, a new era started in which we have direct experimental information on the physics behind the breaking of the electroweak (EW) symmetry. This breaking plays a fundamental role in our understanding of particle physics and sits at the high-energy frontier beyond which we expect new physics that supersedes the Standard Model (SM). In this review we summarize what we have learned so far from LHC data in this respect. In the absence of new particles having been discovered, we discuss how the scrutiny of the properties of the Higgs boson (in search for deviations from SM expectations) is crucial as it can point the way for physics beyond the SM. We also emphasize how the value of the Higgs mass could have far-reaching implications for the stability of the EW vacuum if there is no new physics up to extremely large energies.     

Pair production of charged Higgs bosons in the left–right twin Higgs model at the ILC and LHC

The left–right twin Higgs (LRTH) model predicts the existence of a pair of charged Higgs bosons φ^±. In this paper, we study the production of the charged Higgs boson pair φ^± at the international linear collider (ILC) and the CERN large hadron collider (LHC). The numerical results show that the production rates are at the level of several tens fb at the ILC, and the process e⁺e^-→φ⁺φ^- can produce adequately distinct multi-jet final states. We also discuss the charged Higgs boson pair production via the process qq̄→φ⁺φ^- at the LHC and estimate in this case the production rates. We find that, as long as the charged Higgs bosons are not too heavy, they can be abundantly produced at the LHC. The possible signatures of these new particles might be detected at the ILC and LHC experiments. PACS 12.60.Fr; 14.80.Mz; 14.65.Ha; 12.15.Lk     

Higgs and Z<Superscript>′</Superscript> phenomenology in B–L extension of the standard model at LHC

The phenomenology of the low scale U(1)_B–L extension of the standard model and its implications at LHC energies is presented. In this model, an extra gauge boson corresponding to B–L gauge symmetry and an extra SM singlet scalar (heavy Higgs boson) are predicted. We show a detailed analysis of both heavy and light Higgs bosons decay and production in addition to the possible decay channels of the new gauge boson. We find that the cross sections of the SM-like Higgs production are reduced by ∼20–30%, while its decay branching ratios remain intact. The extra Higgs boson has relatively small cross sections and the branching ratios of Z^′→l⁺l^- are of order ∼20% to be compared to ∼3% of the SM results. Hence, the search for Z^′ is accessible via a clean dilepton signal at LHC.     

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.     

Single scale factor for the universe from the creation of radiation and matter till the present

For a long time, global fits of the electroweak sector of the standard model (SM) have been used to exploit measurements of electroweak precision observables at lepton colliders (LEP, SLC), together with measurements at hadron colliders (Tevatron, LHC) and accurate theoretical predictions at multi-loop level, to constrain free parameters of the SM, such as the Higgs and top masses. Today, all fundamental SM parameters entering these fits are experimentally determined, including information on the Higgs couplings, and the global fits are used as powerful tools to assess the validity of the theory and to constrain scenarios for new physics. Future measurements at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) promise to improve the experimental precision of key observables used in the fits. This paper presents updated electroweak fit results using the latest NNLO theoretical predictions and prospects for the LHC and ILC. The impact of experimental and theoretical uncertainties is analysed in detail. We compare constraints from the electroweak fit on the Higgs couplings with direct LHC measurements, and we examine present and future prospects of these constraints using a model with modified couplings of the Higgs boson to fermions and bosons.     

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     

Perspectives of SM Higgs measurements at the LHC

The latest unsuccessful Higgs searches at LEP have pushed its mass well into the domain where significant signals can be expected from the LHC experiments. The most sensitive LHC Higgs signatures are reviewed and the discovery year is estimated as a function of the Higgs mass. Finally, we give some ideas about: ‘What might be known about the production and decays of a SM Higgs boson’ after 10 years of LHC?     

h --> mutau at Hadron colliders

We study the observability for a lepton flavor-changing decay of a Higgs boson h--> mutau at Hadron colliders. Flavor-changing couplings of a Higgs boson exist at tree level in models with multiple Higgs doublets. The hmutau coupling is particularly motivated by the favorable interpretation of nu(mu)-nu(tau) oscillation. We find that at the Tevatron run II the unique mutau signature could serve as the Higgs discovery channel, surpassing expectations for Higgs boson searches in the SM and in a large parameter region of the MSSM. The sensitivity will be greatly improved at the LHC, beyond the coverage at a muon collider Higgs factory.     

Pair production of neutral Higgs bosons from the left-right twin Higgs model via γγ collisions

The left-right twin Higgs (LRTH) model predicts the existence of the neutral Higgs bosons (h, φ<'0>), which can be produced in pairs (φ<'0>φ<'0>, hh, φ<'0>h) via γγ collisions at the next generation e<'+>e<'-> International Linear Collider (ILC). Our numerical results show that the production cross section of the neutral Higgs boson pair φ<'0>φ<'0> can reach 8.8 fb. The subprocess γγ→φ<'0>φ<'0> might be used to test the LRTH model in future ILC experiments.