Cristina Martellini

26 August 2024
XIII International Conference on New Frontiers in Physics

Abstract: The Belle II experiment has collected 424 fb$^{-1}$ sample of $e^+e^-$ collisions produced by the asymmetric SuperKEKB collider, at a centre-of-mass energy equal to or near the mass of the $\Upsilon(4S)$ resonance. Ninety-percent of the sample is at the $\Upsilon(4S)$ resonance, which decays to $B$-meson pairs. The predecessor experiment, Belle, collected nearly 1~ab$^{-1}$ of data from 1999-2010, three-quarters of which was at the $\Upsilon(4S)$. From these $\Upsilon(4S)$ data, we have made measurements of rare $B$ decays and $C\!P$ violation, as well as searched for lepton-universality violation. Highlights include the first observation of $B\to K\nu\bar{\nu}$ and measurements of lepton-universality in semitauonic $B$ decays. In addition, we study charm hadron decays, tau decays and quarkonium, which are also produced in abundance at these energies. Using low multiplicity events, we search for dark sector particles and make measurements related to the anomalous magnetic moment of the muon.