T. Eissner

The PANDA Electromagnetic Calorimeter—A High-Resolution Detector Based on PWO-II

The electromagnetic calorimeter of the PANDA detector at the future Facility for Antiproton and Ion Research is one of the central components to measure high-energy photons over a wide dynamic range down to a few tens of mega-electron volts. The calorimeter comprises almost 16 000 PWO-II crystals of 200 mm length with high quality standards in optical performance, light output, and radiation hardness. The running mass production has passed more than 7000 crystals. The observation of stimulated recovery even of cooled crystals by illumination with external light sources integrated into the detector modules has opened up a new design concept for PANDA and future calorimeters.

High-quality PWO crystals for the PANDA-EMC

The paper provides a status report on the crystal production and quality control of a major part of the PbWO 4 crystals for the PANDA-EMC. The results confirm the excellent performance of the new g ...

Influence of the Light Collection Non-Uniformity in Strongly Tapered Lead Tungstate Crystals on the Energy Resolution of the PANDA Electromagnetic Calorimeter at Energies Below 1 GeV

The electromagnetic calorimeter of the PANDA detector at the future FAIR facility, will be one of the central components to achieve the physical goals in studying the interaction of cooled antiprotons with a fixed target. The barrel part of the target electromagnetic calorimeter will consist of 11 crystal geometries with a different degree of tapering. Due to tapering the crystals show a non-uniformity in light collection, which is resulting from an interplay between the focusing and the intrinsic absorption of light in the crystal. For the most tapered crystals the light detected by the photo sensor is enhanced by a factor of > 1.4, if the scintillation light is created in the front part of the crystal. Due to the spread of the electromagnetic shower within the crystal and due to its fluctuations, this effect leads to a smearing of the response, resulting in a reduction of the energy resolution. Therefore, one lateral crystal surface has been de-polished for 9 crystals to a roughness of 0.3 μm, which decreases the non-uniformity from up to 40% to less than 5%, with a tolerable decrease of the light yield. This paper will compare the response of a 3×3 array of crystals with one de-polished side face with an identical matrix of completely polished crystals using high energy photons from 56 MeV up to 767 MeV, respectively. The results are compared to GEANT4 simulations and show a significant improvement of the energy resolution at energies above ~ 200 MeV with no deterioration down to 50 MeV.

Quality of the PbWO 4 crystals for the PANDA-EMC

More than 7,300 PbWO4 crystals of PWO-II quality have been delivered by BTCP (Bogoroditsk Technical Chemical Plant, Russia) and tested, which corresponds to almost 50% of the electromagnetic calorimeter of the future PANDA detector at FAIR. The existing crystals comprise both end caps completely and a small part out of the 2×11 crystal geometries forming the barrel. Beside the verification of the geometrical shape and surface quality the very stringent controlling process focuses on the longitudinal and transversal optical transmittance, radiation hardness and the relevant scintillation parameters such as light output and decay kinetics. All crystals are exposed at room temperature to an integral dose of 30 Gy (60Co) to determine the radiation hardness, which is a crucial parameter due to the operation of the calorimeter at T= −25°C, when recovery mechanisms are slowed down. Significantly less than 10% had to be rejected. The overall performance will be compared to crystal samples of identical geometry provided by SICCAS (Shanghai, China).

Performance of the prototype of the PANDA-EMC

The electromagnetic calorimeter (EMC) in the target region of the future PANDA detector at FAIR is one of the crucial components of the spectrometer to study antiproton annihilations in order to investigate yet undiscovered charm-meson states and glueballs. The calorimeter is composed of cooled PbWO4 crystals arranged in a barrel and two end cap sections. The present paper describes the construction and performance of a fully functioning prototype PROTO60 representing a small section of the barrel. The performance, when operated at a temperature of T=−25°C was determined exploiting cosmic muons and energy marked photons from the MAMI-C accelerator (Mainz, Germany) up to photon energies of 1.4 GeV. The response was measured with sampling as well as charge-integrating ADCs for a comparative study. Energy, position and time resolutions are discussed in detail and compared to expectations based on previous tests and simulations. The obtained results fulfil already the required limit set by the envisaged physics program of PANDA in spite of several options for further improvement, such as the light collection with an additional large area APD.