https://doi.org/10.1140/epjc/s10052-024-12818-2
Regular Article - Theoretical Physics
Explaining the excess via a massless dark photon
1
Physics Department, University of Trieste, Strada Costiera 11, 34151, Trieste, Italy
2
INFN, Sezione di Trieste, Via Valerio 2, 34127, Trieste, Italy
3
NICPB, Rävala 10, 10143, Tallinn, Estonia
Received:
15
February
2024
Accepted:
14
April
2024
Published online:
4
May
2024
The Belle II collaboration has recently observed the rare decay , finding an excess with respect to the Standard Model prediction. We explore the possibility that the data entails long-distance interactions induced by a massless dark photon, . This couples at the tree-level to an invisible, dark sector and to the Standard Model via higher-dimensional operators, such as the chromomagnetic-dipole coupling that we use to explain the excess. As the process is forbidden by angular momentum conservation, the transition mediated by the off-shell dark photon yields a three-body final state comprising a pair of dark fermions that show as a missing energy continuum in the detector, faking the neutrino signature. We show that the Belle II data is explained for perturbative values of the parameters of the model. This scenario predicts new contributions to the neutral B meson decays , in which the emission of a on-shell dark photon is allowed, yielding a monochromatic missing energy signature. Analogously, an excess due to the emission of a dark photon is predicted for the decay that could be scrutinized next at the LHCb experiments.
© The Author(s) 2024
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