Searching for light vector bosons at e⁺e^- colliders by invisible decay modes

Thi To Uyen Lam^1*, Guey-Lin Lin¹, Yen-Hsun Lin²

¹Institute of Physics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
²Institute of Physics, Academia Sinica, Taipei 115, Taiwan

* Presenter:Thi To Uyen Lam, email:touyen.sc09@nycu.edu.tw

We report on the sensitivity study for the search of single-photon events e⁺e^-→γZ'→γνν in the minimal model U(1)_Lμ-Lτ for the Z' mass up to 8 GeV. We derive the effective coupling between Z' and electron that is induced by one-loop diagram. The signal event number for Belle II design luminosity 50 ab^-1 as a function of U(1)_Lμ-Lτ gauge coupling constant is calculated. Besides, we consider the main sources of background for this search, which are QED processes with three (or more) photons in the final state. This differs from previous works [1, 2] which do not take these backgrounds into account but rather consider much less important background e⁺e^-→γνν mediated by standard model W and Z bosons. We obtain limits on U(1)_Lμ-Lτ gauge coupling constant as a function of m_Z' by inferring from BaBar 2017 dark photon search limit and a correct sensitivity limit to the same coupling constant at Belle II with 50 ab^-1 integrated luminosity. We also derive limits for other new physics models with light neutral gauge bosons.

Keywords: Dark matter, Muon anomalous magnetic moment, Belle II experiment, BaBar experiment