C MacQueen

31 October 2019

Abstract: The first dark sector physics analyses for Belle II are currently underway. Belle II detects collisions at the SuperKEKB asymmetric-energy $e^{+}e^{-}$ collider in Tsukuba, Japan and has already collected $6.5$ fb$^{-1}$ of data at the $\Upsilon(4S)$ resonance ($\sqrt{s} = 10.58$ GeV). The collider has a design luminosity of $8 \times 10^{35}$ cm$^{-2}$ s$^{-1}$ and the detector will collect $50$ ab$^{-1}$ of data in its lifetime, making it the most luminous experiment in the world. In addition to early performance studies on particle identification, tracking quality, energy resolution, and more, Belle II is preparing to release its first physics results. These include the first official time-integrated luminosity measurements, as well as searches for the dark photon, $A^{\prime}$, in a monophoton signature, and the invisible $Z^{\prime}$ in both $L_{\mu}-L_{\tau}$ and Lepton Flavour Violation models. Even with this early data set, it is clear that Belle II is and will continue to be competitive in various dark sector searches at the MeV-GeV scale.

Keyword(s): dark sector ; dark matter ; ALP ; invisible Z' ; dark Z' ; sark photon