Belle II experiment


The Belle II experiment is a particle physics experiment designed to study the properties of B mesons. Belle II is the successor to the Belle experiment, and is currently being commissioned at the SuperKEKB accelerator complex at KEK in Tsukuba, Ibaraki Prefecture, Japan. The Belle II detector was "rolled in" 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 due mostly to a factor 40 increase in instantaneous luminosity provided by SuperKEKB over the original KEKB accelerator.

Detector upgrade

Much of the original Belle detector has been upgraded to cope with the higher instantaneous luminosity provided by the SuperKEKB accelerator. Close to the beam pipe, the two innermost layers of Belle's silicon vertex detector have been replaced by a depleted field effect transistor pixel detector, and a larger the silicon vertex detector. A larger central tracking system – a wire drift chamber, has been installed. Two new particle identification systems have been installed in the forward endcap and in the barrel. The original CsI electromagnetic calorimeter has been re-used. The calorimeter readout electronics have been upgraded. Finally, scintillators have been installed in the forward endcap and inner layers of Belle's and muon detector, the original resistive plate chambers from Belle are reused in the outer layers of the barrel.
The target dataset is 50ab−1 at Belle II compared to 988fb−1 at Belle.

Timeline

The Belle II data taking is separated into three phases:
On March 25th 2019 the first collisions of the real physics program could be detected with the nearly complete Belle II detector (only half of the pixel detector is installed. The installation of the full pixel detector is planned for 2020.