Elsevier

Nuclear Physics B

Volume 962, January 2021, 115237
Nuclear Physics B

Signatures of a flavor changing Z′ boson in Bq → γZ

https://doi.org/10.1016/j.nuclphysb.2020.115237Get rights and content
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Abstract

Rare B meson decays offer an opportunity to probe a light hidden Z boson. In this work we explore a new channel BqγZ (q=d,s) followed by a cascade decay of Z into an invisible (neutrino or dark matter) or charged lepton pair + (=e,μ). The study is based on a simplified effective model where the down quark sector has tiny flavor-changing neutral current couplings with Z. For the first time, we calculate BR(BqγZ) at the leading power of 1/mb and 1/Eγ. Confronting with the strong constraints from semi-invisible decays of B meson, we find that the branching ratio for Bdinvisible+γ can be larger than its Standard Model background prediction, leaving a large room for new physics, in particular for light dark matter. Additionally, the branching ratio for Bde+eγ can also be sizable when the corresponding flavor violating Z coupling to quarks is of the axial-vector type. On the other hand, the predicted branching ratios of Bdμ+μγ and Bs+γ are severely constrained by the experimental measurements.

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