Decay width modeling of Higgs boson within THDM model
aa r X i v : . [ h e p - ph ] J a n Decay width modeling of Higgs boson withinTHDM model
T.V. Obikhod and I.A. Petrenko
Institute for Nuclear ResearchNational Academy of Sciences of Ukraine03068 Kiev, Ukraine e-mail: [email protected]
Abstract
As part of the search for new physics beyond the StandardModel, we chose the determination of the Higgs boson decaywidth as one of the least experimentally determined values. Thedecay widths into the four fermions of the lightest and heaviestCP-even Higgs bosons of the THDM model were calculated, tak-ing into account QCD and electroweak corrections in the NLOapproximation. To achieve this goal, the program Monte CarloProphecy 4f with special scenarios of parameters, 7B1 and 5B1were used. It was found that the decay width of the heavierCP-even Higgs boson, H differs from H SM by 1227.93 times andchanges to a negative value when deviating from the standardscenarios. Scale factors k Z and k W showed the predominanceof the associated with Z boson production cross section of CP-even Higgs boson over the associated with W production crosssection. . Introduction In light of the latest experimental data on the searches for newphysics beyond the Standard model (SM), Higgs boson remainsthe only candidate for a window into new physics, [1]. This taskis related to the experimental study and theoretical predictionsof the properties of the Higgs boson: the production cross sec-tions, the partial decay width, coupling measurements, k i . Thecrucial role for the investigation of the Higgs boson propertiesis played by the Higgs branching ratios and decay widths, [2].The Higgs particle is a massive scalar boson with zero spin, noelectric charge, and no colour charge is very unstable, decayingimmediately into other particles. As all the channels of decayof the Higgs boson as well as possible new particles with cer-tain masses have not yet been studied, there are uncertaintiesin the properties of the coupling constants and, accordingly, inthe decay width of this particle. This fact is demonstrated bythe deviation of the predicted SM Higgs decay width of about4 . · − GeV from the experimental data, which are presentedin Table 1, [3, 4].
Table 1.
Run 1 observed (expected) direct 95% CL constraints on the width ofthe 125 GeV resonance from fits to the γγ and ZZ mass spectra. The CMSmeasurement from the 4l mass line-shape was performed using Run 2 data. Experiment M γγ M l ATLAS ≺ . .
2) GeV ≺ . .
2) GeVCMS ≺ . .
1) GeV ≺ . .
6) GeVThe purpose of our paper is to calculate decay widths oflightest, h, and CP-even, H, Higgs bosons of Two Higgs doubletmodel (THDM), [5] as well as the value of the deviation fromSM of the sum of the partial Higgs decay widths compared tothe SM, κ H , through computer modeling with the help of MonteCarlo program Prophecy 4f 3.0 [6]. . The calculations of decay width and scale factors The Standard Model predicts a very small width of about 4MeV for a 126 GeV Higgs boson. But the error of the energymeasurement at the LHC is hundreds of times greater, of theorder of 1 GeV, and it will not be possible to significantly reduceit. As a result, measuring the width of the Higgs boson directlyis unrealistic. However, it is possible to accumulate data on theproduction and decay of the Higgs boson at significantly higherenergies - not in the vicinity of 126 GeV, but, say, above 300GeV, [7]. This process will look like the birth and decay of avirtual Higgs boson in this mass range. It is, of course, stronglyweakened in comparison with the main process at the resonancepeak, but it can be quite measurable.As THDM model predicts the existence of five Higgs bosons,we will carry out our calculations for two bosons: lightest Higgsboson, h and CP-even Higgs boson, H as the analog of virtualHiggs boson described above. Thus, the idea of theorists - toaccumulate data on the production and decay of the Higgs bosonat significantly higher energies can be realized. The efficiency ofthis method can be estimated by comparing the calculations ofdecay widths for the lightest and heaviest bosons.The precise experimental investigation of the Higgs bosonand theoretical searches for deviations from the predictions of SM requires precise Monte Carlo computer modeling. Prophecy4f computes the inclusive partial decay widths and differentialdistributions of the decay products, where unweighted eventsfor leptonic final states are provided. The advantage of theProphecy4f program is that it allows the calculations for theHiggs decays into four fermions including full electroweak andQCD next-to-leading order (NLO) corrections with interferencecontributions between different W W / Z Z channels, and inclu-sion of all off-shell effects of intermediate
W/Z bosons.We’ll consider the processes, LO Feynman diagram of which s in the form of Fig. 1 Fig.1.
Generic diagram for decay of H → f where V = W, Z , from [6].
The total state width of Higgs boson is equal to the sum of thepartial channel widths [6]:Γ H → f = Γ total = Γ leptonic + Γ semi − leptonic + Γ hadronic , The total width can be presented via
Z Z , W W decays andtheir interference:Γ H → f = Γ H → W ∗ W ∗ → f + + Γ H → Z ∗ Z ∗ → f + Γ W W/ZZ − int , where the components are defined in terms of specific final states:Γ H → W ⋆ W ⋆ → f = 9 · Γ H → ν e eµ − ν µ + 12 · Γ H → ν e edu + 4 · Γ H → udsc , Γ H → Z ∗ Z ∗ → f = 3 · Γ H → ν e ν e ν µ ν µ + 3 · Γ H → eeµµ + + 9 · Γ H → ν e ν e µµ + + 3 · Γ H → ν e ν e ν e ν e + 3 · Γ H → eeee + 6 · Γ H → ν e ν e uu + 9 · Γ H → ν e ν e dd + 6 · Γ H → uuee + 9 · Γ H → ddee + 1 · Γ H → uucc + 3 · Γ H → ddss + 6 · Γ H → uuss + 2 · Γ H → uuuu + 3 · Γ H → dddd , Γ W W/ZZ − int = 3 · Γ H → ν e eeν e − · Γ H → ν e ν e µµ + − · Γ H → ν e eµν µ +2 · Γ H → uddu − · Γ H → uuss − · Γ H → udsc . sing scenarios obtained from the experimental measurements,[8], we presented the calculated NLO results on the four-fermiondecays of light C P -even Higgs boson, h , Table 2 Table 2.
Decay widths of lightest Higgs boson, h . Full decaywidth oflightestHiggsboson, h ,(MeV) Γ → W W Γ → Z Z Γ int Table 3.
THDM input parameters. M H , GeV M H + , GeV M A , GeV λ tan β c αβ I 360 690 420 -1.9 4.5 0.15II 600 690 690 -1.9 4.5 0.15
Table 4.
Decay width of
C P -even Higgs boson, H . Full decaywidth oflightestHiggsboson, h ,(MeV) Γ → W W Γ → Z Z Γ int -54.487 -71.47 17.203 -0.221176.36 789.98 385.74 0.64The calculations of SM Higgs boson decay width give us thefollowing result, Table 5 able 5. Decay width of SM Higgs boson, H SM Full decaywidth oflightestHiggsboson, h ,(MeV) Γ → W W Γ → Z Z Γ int κ H is the value of the deviation of the sum ofthe partial Higgs decay widths compared to the SM total widthΓ SMH , [9, 10]: κ H ( κ i , m H ) = X j = W W ⋆ ,ZZ ⋆ ,bb,τ − τ + ,γγ,Zγ,gg,tt,cc,ss,µ − µ + Γ j ( κ i , m H )Γ SMH ( m H ) . Since the identification of four leptons is the most detectabledecay mode in comparison with other decay channels, the opti-mal direction of the search for new physics will be finding andcomparison of the factor κ H for the decays of two Higgs bosons— the lightest and the heaviest one into W W or Z Z bosons.So, the scale factor κ H in this case is the following: κ H ( κ i , m H ) = X j = W W ⋆ , ZZ ⋆ Γ j ( κ i , m H )Γ SMH ( m H ) . It is also interesting to calculate scale factors κ W and κ Z Γ W W ∗ Γ SMW W ∗ = κ W , Γ ZZ ∗ Γ SMZZ ∗ = κ Z , which allow probing for BSM contributions in the loops for eachchannel separately. Moreover, these factors make it possible to alculate the deviations from the SM of the associated produc-tion cross sections in accordance with the formulas: σ W H σ SMW H = κ W ,σ ZH σ SMZH = κ Z . The results of our calculations are performed in the Table 6:
Table 6.
Scaling factors of two Higgs bosons
Scenario κ W κ Z κ H w/oint κ H winth 5-B1 0.97 0.939 0.967 0.969h 7-B1 0.968 0.97 0.969 0.971H II 921 3597 1218 1228From the comparison of the data from Table 6 we see theslight change in κ H factor for 5-B1 and 7-B1 scenarios and hugeincrease compared to SM one for scenario II. Moreover, we cansee the increasing of κ H factor for all scenarios with inclusionof interference. The BSM contributions in the loops for W W channel are larger in 5-B1 scenario but for 7-B1 scenario thelarger contribution in the loops are for
Z Z channel. Therefore,the chose of renormalization schema is also essential to the finalresult. The sharp jump in the κ H factor for heavier C P -evenHiggs boson indicates about significant deviation from the SM for scenario 7-B1. The difference in factor κ Z compared to κ W byalmost four times indicates the predominance of the associatedwith Z boson production cross section of C P -even Higgs bosonover the associated with W production cross section. . Conclusions The searches for BSM physics are connected with studyingof Higgs boson properties. The way of the realization of thispurpose is connected with the decay widths measurements andtheoretical predictions of Higgs boson properties. The most per-spective and convenient Higgs boson decay channel into fourfermions is one of the interesting way of its investigation. Forthe precise measurements of the decay width is proposed THDMmodel in the paper. We have considered lightest and CP-evenheavier Higgs bosons, h and H correspondingly and modeledtheir decay widths into four fermions with the help of MonteCarlo program Prophecy 4f 3.0. The results of our calculationsled us to the following conclusions connected with the searchesof deviations from SM: • decay widths of lightest Higgs boson, h and H SM almostdo not differ from each other; • the scale factor κ H of C P -even Higgs boson, H equal to1228; • the calculations of decay widths strongly depend on the pa-rameter space and can take negative values as the masses ofthe C P -even and
C P -odd Higgs bosons decrease by almosttwo times from the parameters of the 7B1 scenario; • the interference account leads to an insignificant increasein decay widths; • the difference in factor κ Z compared to κ W by almost fourtimes indicates the predominance of the associated with Z boson production cross section of C P -even Higgs boson, H over the associated with W production cross section. • BSM contributions in the loops for
W W and
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