The SuperKEKB accelerator has just passed its first major luminosity milestone and achieved a luminosity above 10^33/cm^2/sec. On April 25, 2018 Belle II observed its first collisions at SuperKEKB. Less than a month later, after a great deal of accelerator tuning and focusing of the beam, SuperKEKB has just achieved a luminosity of 1.34 x 10^33/cm^2/sec, which is a bit above the peak luminosity of the CESR accelerator at Cornell (1.25 x 10^33/cm^2/sec). More SuperKEKB luminosity milestones are expected in the coming months.
The Belle II detector, installed at the collision point, recorded events from electron-positron annihilation (matter-antimatter annihilation) of the beam particles, which produced other particles likely including beauty quark and anti-beauty quark pairs as well as other hadronic and Bhabha scattering events. These are the first electron-positron collisions at the KEK particle physics laboratory in 8 years; the previous KEKB particle collider ceased its operations in 2010.
SuperKEKB will work at the so-called intensity frontier to produce copious amounts of B and D mesons and τ leptons, enabling precise measurements of rare decays that test the SM with unprecedented sensitivity. Since the first beams were stored over a month ago, KEK teams have worked to tune the two beams for first collisions at the centre of the Belle II detector – the “super-B factory” upgrade of its predecessor, Belle. When fully commissioned, Belle II will detect and reconstruct events at the much higher rates provided by the 40-fold higher design luminosity of SuperKEKB compared to KEKB. The Belle II outer detector is already in place, but the full inner detector will not be installed until the end of the year, and the first physics run with the complete detector is projected to start in February 2019.