Belle II experiment

36°9′28″N 140°4′30″E / 36.15778°N 140.07500°E / 36.15778; 140.07500

The Belle II experiment is a particle physics experiment designed to study the properties of B mesons (heavy particles containing a bottom quark) and other particles. Belle II is the successor to the Belle experiment, and commissioned at the SuperKEKB accelerator complex at KEK in Tsukuba, Ibaraki prefecture, Japan. The Belle II detector was "rolled in" (moved into the collision point of SuperKEKB) in April 2017. Belle II started taking data in early 2018. Over its running period, Belle II is expected to collect around 50 times more data than its predecessor, mostly due to a 40-fold increase in an instantaneous luminosity provided by SuperKEKB as compared to the previous KEKB accelerator.

Many interesting analyses of the Belle and BaBar experiments were limited by statistical uncertainties, which was the main motivation to build a new generation of B-factory - Belle II.

The target dataset is 50,000 fb⁻¹ at Belle II compared to 988 fb⁻¹ (with 711 fb⁻¹ at the Υ(4S) energy) at Belle. The dataset of good runs from Belle II before Long shutdown 1 was 424 fb⁻¹ (with 363 fb⁻¹ at the Υ(4S) energy.)

This immense dataset would allow studies of rare physics processes, which were out of reach for the previous e⁺ e⁻ experiments and improve precision on the already measured physics observables.

The physics program of Belle II includes the studies of the following particles or processes:

The majority of the Belle II dataset will be recorded at Upsilon(4S) center-of-mass energy, while a small portion of it will be taken at Upsilon(5S) and as energy scans.

Belle II is a general purpose high-energy particle detector with almost full solid angle coverage. It has a cylindrical shape to cover the e⁺ e⁻ collisions happening on the central axis of the detector. The detector is asymmetric in beam direction, because the initial energy of the electron beam is larger than the positron beam. Much of the original Belle detector has been upgraded to cope with the higher instantaneous luminosity provided by the SuperKEKB accelerator.