Performance of the BGO endcap calorimeter of the CMD-3 detector

The BGO endcap calorimeter was successfully operated in the CMD-2 detector at the VEPP-2M collider. It consists of 680 BGO crystals, each with a size of 25 × 25 × 150 mm³, arranged in two identical endcaps, with a total crystal weight of 450 kg. The light readout used vacuum phototriodes. The endcap calorimeter has been upgraded to operate in the CMD-3 detector at the new collider VEPP-2000. The major part of the endcap calorimeter, the BGO crystals, remains the same. The main upgrade is the use of silicon PIN photodiodes and new electronics. The main reason to change a photosensitive device is the strong non-uniform magnetic field in the endcap calorimeter volume and reduced available space. The Hamamatsu PIN photodiode S3590-08 was chosen as an optimal solution, as it is insensitive to magnetic fields and is both compact and stable. An order of magnitude larger capacitance of silicon photodiodes requires design and produce new custom electronics. The upgrade is expected to bring an overall improvement of parameters. The endcap calorimeter has been installed in the detector and participates in data taking which started in 2010. The preliminary energy resolution is measured in the energy range 160–1000 MeV. It is better to compare to the CMD-2 detector