Probing \u03bc\u03c4 flavor-violating solutions for the muon g \u2212 2 anomaly at Belle II

Syuhei Iguro,Michihisa Takeuchi,Yuji Omura

doi:10.1007/jhep09(2020)144

Syuhei Iguro, Michihisa Takeuchi + Show 1 more

Open Access

https://doi.org/10.1007/jhep09(2020)144

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Abstract

The discrepancy between the measured value and the Standard Model prediction of the muon anomalous magnetic moment is one of the most important issues in the particle physics. It is known that introducing a mediator boson X with the μτ lepton flavor violating (LFV) couplings is one good solution to explain the discrepancy, due to the τ mass enhancement in the one-loop correction. In this paper, we study the signal of this model, i.e. the same-sign leptons, in the Belle II experiment, assuming the flavor-diagonal couplings are suppressed. We show that the Belle II experiment is highly sensitive to the scenario in the mediator mass range of O(1–10) GeV, using the e+e−→ μ±τ∓X → μ±μ±τ∓τ∓ process induced by the X .

Highlights

One well-known way to enhance the new physics contribution keeping the coupling size small is introducing a mediator with flavor violation couplings
We show that the Belle II experiment is highly sensitive to the scenario in the mediator mass range of O(1–10) GeV, using the e+e− → μ±τ ∓X → μ±μ±τ ∓τ ∓ process induced by the X
We discussed the models with a scalar and vector mediator with μτ flavor violating couplings, and explicitly show that relatively small coupling can explain the discrepancy in both models due to the chirality enhancement by a factor of mτ /mμ in the muon g − 2 contribution

Summary

Scalar scenario

We discuss a model with a new scalar mediator for the first. Following the ALP scenario, we introduce the interaction as follows [12]. Where a is ALP, that is a scalar mediator, and Vilj (alij) are the vector (axial vector) couplings. The scalar gains non-vanishing mass, ma, as the ALP usually does, in our model. In this setup, we have three independent parameters: the mass of the ALP particle ma, scalar coupling Vμlτ , and pseudo scalar coupling alμτ. Vμlτ to obtain the central value for δaμ is plotted on the ma vs Ra plane with Λ = 1 TeV. The required value of Vμlτ to explain the muon g − 2 anomaly as a function of ma is shown for each selected coupling ratio: Ra = 0.8 (blue), 0.6 (orange), and.

Vector scenario

Collider signals at the Belle II experiment

Signal and kinematic cut

Sensitivity

Conclusion and discussion