On Nov. 16 2016, a data acquisition system for the silicon pixel detector of the Belle II experiment (the ONSEN system) was shipped to DESY laboratory, to be further integrated with other parts of the silicon pixel detector (PXD). It will then go through beam tests by Giessen University and other DEPFET (Depleted Field Effect Transistors) collaboration members. This will be the last step before final installation at Belle II in Japan.

The ONSEN system was designed and constructed by IHEP and is compliant to the new xTCA standard (PICMG 3.8 specification). This has proved to be another example of IHEP’s leading capability in designing and constructing instrumentation for particle physics experiments. 

The DEPFET international collaboration is led by the Munich Max Planck Institute, and includes more than ten other European institutes and IHEP. It focuses on the design and application of silicon pixel detectors in medical science, astronomy and cosmic ray experimental physics, and high energy particle physics.

As an application in high energy particle physics, the DEPFET detector will be used as the innermost tracking detector of the Belle II detector, providing the vertex position of decay particles. The electronics data output of the DEPFET detector is so great, at a level of 240 Gbps, that it must be stored temporarily for 4 seconds and compressed to one tenth of the original size, before being sent for high level event processing.

IHEP researchers used their experience in trigger and DAQ design and collaboration with Giessen University, and the leading design capability in the high throughput and high speed interconnection provided by the xTCA PICMG 3.8 specification, to design and build the ONSEN system and thus contribute in-kind to the Belle II collaboration. This will allow Chinese physicists to share Belle II experiment data for physics analysis, as noted in a special DEPFET-BELLE II-IHEP memorandum.