Displaced Searches for Light Vector Bosons at Belle II

Abstract

With a design luminosity of 50 ab${}^{-1}$ and detectors with tracking capabilities extending beyond 1 m, the Belle II experiment is the perfect laboratory for the search of particles that couple weakly to the Standard Model and have a characteristic decay length of a few centimetres and more. We show that for models of dark photons and other light vector bosons, Belle II will be successful in probing regions of parameter space which are as of now unexplored by any experiment. In addition, for models where the vector boson couples sub-dominantly to the electron and quarks as compared to muons, e.g. in the $L_{\mu }-L_{\tau }$ model, Belle II will probe regions of mass and couplings compatible with the anomalous magnetic moment of muon. We discuss these results and derive the projected sensitivity of Belle II for a handful of other models. Finally, even with the currently accumulated data, $\sim 200$ fb${}^{-1}$, Belle II should be able to cover regions of parameter space pertaining to the X(17) boson postulated to solve the ATOMKI anomaly.

Published version. 19 pages, 8 figures. Minor Changes

References in corpus (12)

• Measurement of the fine-structure constant as a test of the Standard Model
• Secluded U(1) below the weak scale
• New Fixed-Target Experiments to Search for Dark Gauge Forces
• U-boson production in e+e- annihilations, psi and Upsilon decays, and Light Dark Matter
• New Limits on Hidden Photons from Past Electron Beam Dumps
• Search for $A^{\prime }\to {\mu }^{+}{\mu }^{-}$ decays
• Search for light massive gauge bosons as an explanation of the $(g-2{)}_{\mu }$ anomaly at MAMI
• Kinetic Mixing as the Origin of Light Dark Scales
• Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays
• Refined Bounds on MeV-scale Thermal Dark Sectors from BBN and the CMB
• New weakly-coupled forces hidden in low-energy QCD
• Invisible and displaced dark matter signatures at Belle II