Dark sector searches at Belle II

The Belle II experiment at the SuperKEKB asymmetric energy e+e− collider is a substantial upgrade of the B factory facility at the Japanese KEK laboratory. The design luminosity of the machine is 8×10 cm−2s−1 and the Belle II experiment aims to record 50 ab−1 of data, a factor of 50 more than its predecessor. During 2018, the machine has completed a commissioning run, recording a data sample corresponding to an integrated luminosity of about 0.5 fb−1. Main operations started in March 2019 with the complete Belle II detector; an integrated luminosity of 60 fb−1 has been collected so far. These early data sets, with specifically designed low multiplicity triggers, offer already the possibility to search for a large variety of dark-sector particles in the GeV mass range, complementary to the sensitivities of the LHC and to dedicated low-energy experiments. These proceedings review the status of the dark-sector searches at Belle II, with a focus on the discovery potential with early data, and show the first results. 1 Belle II and SuperKEKB SuperKEKB is an asymmetric energy e+e−collider located in Tsukuba, Japan. The beam energies are chosen such that the resulting centre-of-mass energy is equal to 10.58 GeV, which is the mass of the Υ(4S). As this bb̄ resonance decays mostly into a pair of B mesons, SuperKEKB is called a B factory. Higher beam currents combined with a smaller beam spot will allow SuperKEKB to reach an instantaneous luminosity of 8× 10 cm−2s−1, which is 40 times higher than what its predecessor KEKB achieved. The Belle II experiment is located at the interaction region of the electron and positron beams of SuperKEKB. It consists of different layers of subdetectors arranged concentrically with the vertex detectors being closest to the beam pipe. These are surrounded by a central drift chamber, followed by an electromagnetic calorimeter and the outermost detector responsible for KL and muon reconstruction. 1 1 Michel Bertemes HEPHY Vienna μ+