Belle II gets a new heart: The new pixel detector PXD2 has arrived in Japan


A powerful successor for the innermost detector

At the moment, the SuperKEKB accelerator in Japan is at a standstill. One of the main reasons for this is the planned installation of the new two-layer Belle II Pixel Vertex Detector (PXD2). The greatly improved small detector, which is responsible for measuring the shortest-lived particle decays in the Belle II detector, is scheduled to replace the current PXD1. This is necessary in view of future data taking periods with higher luminosity and the associated larger hit density on the sensors located only a few millimeters from the beam axis to avoid performance degradation for physics analyses.

Intensive preparation for the exchange

The PXD2, like its predecessor, was mostly built at the German institutes of the collaboration. The DEPFET active pixel sensors itself and the modules were developed and manufactured exclusively at the MPG HLL. After many months of intensive preparation at the various German institutes, the time had finally come: the two half-shells of the new PXD2 could be sent on the long journey to Japan. The small sensitive detector consists of ultra-thin and therefore fragile silicon sensors, which have to be protected against shocks in the best possible way. The transport of this unique and irreplaceable instrument was therefore a very special challenge.

The PXD2 was allowed to travel to Japan as a special passenger

In order not to let it out of sight for a moment, a separate seat was reserved for the detector on the aircraft. Bypassing the queues of waiting passengers, the special passenger was then let onto the aircraft first and stowed safely in his seat. To the great relief of all involved, an initial visual inspection of the two half-shells after arrival at the KEK showed no evidence of transport damage.

An important step towards new physics results

In the next few weeks, the detector will be mounted on the beam pipe, which is also new and manufactured at the KEK, and connected to the readout electronics to also verify full electrical functionality. In winter 2023-2024, the SuperKEKB should finally be put back into operation and we expect new exciting results.

The German working groups in the Belle II experiment are supported with funding from the following institutions and programs:

  • Alexander von Humboldt Foundation
  • Bundesministerium für Bildung und Forschung (BMBF)
  • Deutsche Forschungsgemeinschaft (DFG), insbesondere im Rahmen der Exzellenzstrategie des Bundes und der Länder:
    • „ORIGINS“: EXC-2094 – 390783311
    • “Quantum Universe”: EXC-2121 – 390833306
  • European Research Council
  • European Union’s Horizon 2020 – grant agreement No 822070
  • Helmholtz-Gemeinschaft
  • Max-Planck-Gesellschaft
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