Marcello Campajola

25 January 2021

Abstract: Understanding the nature of dark matter is one of the most exciting challenges in fundamental physics nowadays, requiring the synergy of different search techniques, as well as theoretical inputs. An interesting direction for the investigation of dark matter is the one offered by the \textit{B}-factories. Belle II experiment at the SuperKEKB energy-asymmetric $e^+e^-$ collider is a substantial upgrade of the \textit{B}-factory facility at the Japanese KEK laboratory. With a machine design luminosity of $6\times10^{35}\,\rm{cm}^{-2}s^{-1}$, the Belle II experiment aims to record 50 ab$^{-1}$ of data: a factor of 50 more than its predecessor. Thanks to this large data-sample and by using dedicated triggers the Belle II experiment is expected to explore dark sector candidates with an unprecedented sensitivity in a mass range up to 10 GeV$/c^2$. During 2018, the machine has completed a commissioning run, recording a data-sample corresponding to an integrated luminosity of about 0.5 fb$^{-1}$, while main operations started on March 2019 with an almost complete detector. An integrated luminosity of $\sim 90\, \rm{fb}^{-1}$ has been collected so far. These early data sets offer already the possibility to search for a large variety of dark sector particles in the GeV mass range. This paper reviews the status of the dark-sector searches at Belle II, with a focus on the first obtained results, and the discovery potential with the data-set available in the short term.

Keyword(s): Low-mass Dark Matter, Dark Sector, Dark Photon, Axion-Like Particles, Belle II, \textit{B}--factories