TY - JOUR

T1 - Bs to l+ l- gamma as a Test of Lepton Flavor Universality

AU - Guadagnoli, Diego

AU - Reboud, Meril

AU - Zwicky, Roman

N1 - 21 pages, 4 figures. Main modifications in v3: minor textual edits, references added. Matches journal version

PY - 2017/8/8

Y1 - 2017/8/8

N2 - We discuss a number of strategies to reduce the BR(Bs to l+ l- gamma) 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 BR(Bs to l+ l- gamma) and the measured BR(Bs to phi (to K+ K-) gamma). For high q^2, 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 R_gamma, akin to R_K 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.

AB - We discuss a number of strategies to reduce the BR(Bs to l+ l- gamma) 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 BR(Bs to l+ l- gamma) and the measured BR(Bs to phi (to K+ K-) gamma). For high q^2, 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 R_gamma, akin to R_K 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.

KW - hep-ph

U2 - 10.1007/JHEP11(2017)184

DO - 10.1007/JHEP11(2017)184

M3 - Article

SN - 1029-8479

JO - Journal of High Energy Physics

JF - Journal of High Energy Physics

ER -