Abstract
We discuss a number of strategies to reduce the ℬ(B 0 s → ℓ+ℓ−γ) theoretical error, and make such a measurement a new probe of the interactions that are interesting in the light of present-day flavor discrepancies. In particular, for low di-lepton invariant mass we propose to exploit the close parenthood between ℬ(B 0 s → ℓ+ℓ−γ) and the measured ℬ(B 0 s → ϕ(→K+K−)γ). For high q2, conversely, we exploit the fact that the decay is dominated by two form-factor combinations, plus contributions from broad charmonium that we model accordingly. We construct the ratio Rγ , akin to RK and likewise sensitive to lepton-universality violation. Provided the two rates in this ratio are integrated in a suitable region that minimises bremsstrahlung contributions while maximising statistics, the ratio is very close to unity and the form-factor dependence cancels to an extent that makes it a new valuable probe of lepton-universality violating contributions in the effective Hamiltonian. We finally speculate on additional ideas to extract short-distance information from resonance regions, which are theoretically interesting but statistically limited at present.
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Guadagnoli, D., Reboud, M. & Zwicky, R. B 0 s → ℓ+ℓ−γ as a test of lepton flavor universality. J. High Energ. Phys. 2017, 184 (2017). https://doi.org/10.1007/JHEP11(2017)184
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DOI: https://doi.org/10.1007/JHEP11(2017)184