Di-photon Higgs decay in the MSSM with explicit CP violation
aa r X i v : . [ h e p - ph ] D ec Di-photon Higgs decay in the MSSM with explicitCP violation
S Hesselbach , *, S Moretti , , S Munir and P Poulose , School of Physics & Astronomy, University of Southampton, Highfield, SouthamptonSO17 1BJ, UK Laboratoire de Physique Th´eorique, Universit´e Paris–Sud, F–91405 Orsay Cedex, France Physics Department, IIT Guwahati, Assam, INDIA - 781039E-mail: [email protected]
Abstract.
The Minimal Supersymmetric Standard Model (MSSM) with explicit CP violationis studied with the help of the di-photon decay channel of the lightest neutral Higgs boson.Effects of CP violation, entering via the scalar/pseudo-scalar mixing at higher order as well asthrough the Higgs-sfermion-sfermion couplings at tree-level, are analyzed in the MSSM withand without light sparticles. A light stop may have a strong impact on the decay width andBranching Ratio (BR) of the decay process H → γγ , whereas other light sparticles have onlylittle influence. In some regions of the MSSM parameter space with large CP-violating phase φ µ ∼ ◦ a light stop can change the BR by more than 50%.
1. Introduction
Supersymmetry (SUSY) is one of the most favoured scenarios of new physics and will be searchedfor in all possible ways at the upcoming Large Hadron Collider (LHC) at CERN. In the MinimalSupersymmetric Standard Model (MSSM) many parameters can well be complex and thusexplicitly break CP invariance inducing CP violation also in the Higgs sector beyond Bornapproximation [1]. After elimination of unphysical phases and imposing universality conditionsat the unification scale two independent phases remain, the phase φ µ of the higgsino mass term µ and a common phase φ A f of the soft trilinear Yukawa couplings A f in the sfermion sector [2].Despite the fact that the SUSY phases may be severely constrained by bounds on the ElectricDipole Moments (EDMs), these constraints are rather model dependent and may be evaded inscenarios with heavy first and second generation sfermions, due to cancellations among variouscontributions to the EDMs or due to additional contributions from lepton flavour violating termsin the Lagrangian, for a review see e.g. [3].In this contribution we study the di-photon decay mode, H → γγ , of the lightest neutralHiggs boson H , which involves direct, i.e leading, effects of the SUSY phases through couplingsof the H to SUSY particles in the loops as well as indirect, i.e. sub-leading, effects throughthe scalar/pseudo-scalar mixing yielding the Higgs mass-eigenstate H . In scenarios with heavySUSY particles, where the CP violation enters solely through the scalar/pseudo-scalar mixing,the SUSY CP phases can result in a strong suppression of the branching ratio (BR) of the decay H → γγ as well as of the rate of the combined production and decay process gg → H → γγ * Speaker
20 40 60 80 100 120 100 150 200 250 300 M H G e V M H + GeV tan β = 2tan β = 5tan β = 20tan β = 50M U = 1 TeV | µ | = 1 TeV |A f | = 1.5 TeV989592 tan β = 2 tan β = 5 tan β = 20 tan β = 50
20 40 60 80 100 120 100 150 200 250 300 M H G e V M H + GeV tan β = 2tan β = 5tan β = 20tan β = 50M U = 250 GeV | µ | = 1 TeV |A f | = 1.5 TeV939087 tan β = 2 tan β = 5 tan β = 20 tan β = 50 Figure 1.
Mass of the lightest neutral Higgs boson H for φ µ = 0 ◦ (solid, red line) and φ µ = 90 ◦ (dashed, green line) with | A f | = 1 . | µ | = 1 TeV and different values of tan β . In the leftplot all sparticles are heavy ( ∼ M ˜ U = M ˜ Q = M SUSY = 1 TeV, whereas in theright plot a light stop ( ∼
200 GeV) is present for M ˜ U = 250 GeV and M ˜ Q = M SUSY = 1 TeV.[4]. Here, we summarize the results of [5, 6] focusing especially on the effects of light SUSYparticles on the decay H → γγ . The analysis of the full production and decay process at theLHC is postponed to a forthcoming publication [7].
2. Di-photon Higgs decay in CP-violating MSSM
In order to analyze the Higgs decays in the CP-violating MSSM we have used the publiclyavailable
Fortran code
CPSuperH [8], version 2, which calculates the mass spectrum anddecay widths of all Higgs bosons along with their couplings to SM and SUSY particles.The leading terms in the CP-violating scalar/pseudo-scalar mixing in the Higgs sector areproportional to Im( µA f ), hence we assume φ A f = 0 and analyze the effects of nonzero φ µ in the following.A random parameter space scan to study the general behaviour of the BR( H → γγ ) fornon-zero φ µ has revealed that about 50% deviations are possible for M H around 104 GeVfor φ µ = 100 ◦ , and an average of 30% deviation occurs over the mass range 90–130 GeV.Furthermore, a strong impact of a light stop ˜ t on the BR has been established [5]. In [6] theseresults have been consolidated by analyzing the details at the matrix element level including thephase dependence of the Higgs mixing matrix elements and of the respective couplings and byperforming a more thorough study of the dependence on the SUSY parameters.In figure 1 the mass of H is shown as a function of the mass of the charged Higgs boson( M H + ) for φ µ = 0 ◦ , ◦ , tan β = 2 , , ,
50 and the two cases M ˜ U = M ˜ Q = M SUSY = 1 TeV,where all SUSY particles are heavy, and M ˜ U = 250 GeV and M ˜ Q = M SUSY = 1 TeV, where alight ˜ t with mass ∼
200 GeV is present. While in the low tan β case the mass shift induced bythe change in φ µ from 0 ◦ to 90 ◦ is about 10%, in the case of tan β = 20 or above it is about 1%or less. The sudden shift in the dependence of M H on M H + around M H + = 150 GeV is due toa cross over in the Higgs mass eigenstates at that point, where all three neutral Higgs states areapproximately degenerate in mass around 120 GeV.Figure 2 shows the BR( H → γγ ) for five representative φ µ values between 0 ◦ and 180 ◦ as afunction of M H + for the two cases M ˜ U = 1 TeV (all SUSY particles heavy) and M ˜ U = 250 GeV(light ˜ t ). The respective values of M H are indicated separately on the horizontal lines abovefor each φ µ value. Again the cross over point in the Higgs mass eigenstates at M H + ∼
150 GeVis clearly visible. Below this point the BRs are very small and there is a strong φ µ dependence of B R ( H - > γ γ ) M H + GeV M H G e V ϕ µ = 0 ϕ µ = 40 ϕ µ = 90 ϕ µ = 140 ϕ µ = 180 ϕ µ =0 ϕ µ =40 o ϕ µ =90 o ϕ µ =140 o ϕ µ =180 o B R ( H - > γ γ ) M H + GeV M H G e V ϕ µ = 0 ϕ µ = 40 ϕ µ = 90 ϕ µ = 140 ϕ µ = 180 ϕ µ =0 ϕ µ =40 o ϕ µ =90 o ϕ µ =140 o ϕ µ =180 o Figure 2.
BR of H → γγ for | A f | = 1 . | µ | = 1 TeV and tan β = 20. Values of M H corresponding to representative points on the M H + axis are indicated on the horizontallines above separately for the values of φ µ used. The left plot corresponds to the case with M ˜ U = 1 TeV (no light SUSY particles), while the right plot corresponds to the case with M ˜ U = 250 GeV (a light stop is present). M H , hence our analysis is not relevant in this parameter region. Above M H + ∼
150 GeV with M H &
115 GeV the φ µ dependence of M H is within the expected experimental uncertainty andthe BR is large enough to be important for the LHC Higgs search. In scenarios with heavy SUSYparticles (left plot) the BR increases with increasing φ µ leading to a 50% increase for φ µ = 90 ◦ at M H + ∼
200 GeV. This φ µ dependence is caused mainly by the φ µ dependence of the H couplings to W ± bosons and t and b quarks which appear in the loop-induced decay H → γγ .When a light ˜ t is present the additional φ µ dependence in the stop sector causes a considerablechange of the φ µ dependence of the BR. First the BR increases again with increasing φ µ up to amaximum for some value of φ µ around 40 ◦ , beyond which, however, the BR decreases to about50% at φ µ = 180 ◦ .Concerning the dependence on other SUSY parameters we have found that a smaller valueof | A f | considerably changes the φ µ dependence of the BR in scenarios with light ˜ t , whereas asmaller | µ | value leads generally to a smaller φ µ dependence. Other light SUSY particles haveonly a negligible effect on the BR.
3. Summary
We have analyzed the BR of the di-photon decay of the lightest Higgs boson in the CP-violatingMSSM with complex µ parameter. We have found that the strong φ µ dependence of the BRconsiderably changes in the presence of a light scalar top ˜ t . In general, the BR may be increasedor decreased for a non-zero φ µ depending on the SUSY parameter point. References [1] Pilaftsis A 1998
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