In 2011, the green light was given for a major scientific project. Over the last eight years, the KEK particle accelerator and the Belle detector have been extensively modernized. The objective is to improve the system's performance: in future, there will be 40 times more collisions between electrons and positrons, enabling scientists to analyse their decay accordingly.
The new SuperKEKB reported the first particle collisions just a few months ago, and the Belle II detector is now also nearly complete. After successful testing with BEAST, the vertex detector – the final component of Belle II – will be installed over the next few months. This detector is located directly at the point of collision and measures the decay events with maximum precision.
Installing the vertex detector
The Max Planck Institute for Physics was significantly involved in the development and construction of the pixel detector (PXD), one of the two components of the vertex detector (VXD). Over the next few weeks, the pixel detector will be combined with silicon detectors before being put into position in Belle II in December 2018. Initially, the engineers will only be installing one layer of the PXD. The second layer – there are 20 modules in all – will follow as soon as the SuperKEKB accelerator has reached its peak performance.
This will have no effect on the scientific programme, as Hans-Günther Moser, Belle II Project Leader at the Max Planck Institute for Physics explains: “During the test runs with BEAST, we found that we can also obtain optimum measuring results with a reduced number of PXD modules. This means we can spend the first measuring phase gaining experience then apply this to the final expansion of the PXD in 2020.”
Measurements on the spot
The VXD in Belle II has the challenging task of recording traces of particle collisions in resolutions of one hundredth of a millimetre. Collisions between positrons and electrons give rise to B mesons, which in turn decay into other short-lived particles. The physicists hope that the decay patterns of the B mesons will point towards answers to the question of why matter exists in the universe but hardly any anti-matter is left.