A team of two scientists and four students from Shinshu University of Japan and Kyungpook National University of Korea have just packed up their cables, laptops and scintillator strips and left a test beam at DESY with many interesting results in their luggage. They tested the scintillator-strip-based electromagnetic calorimeter (ScECAL), one of the potential layers of a future ILC detector. The electromagnetic calorimeter measures the energy of electromagnetic particles – photons, electrons and positrons –, and ILC calorimeters have the added challenge of particle flow – the complete reconstruction of trajectory, type and energy of every primary particle and the shower particles it produces passing through the detectors.
These plots from the test of a one-layer ScECAL still need calibration of each channel, but a beam shower is already clearly visible.
The (ScECAL) is one of the concepts to achieve this particle flow algorithm. It uses 5-by-45-millimetre scintillator strips whose layers are arranged orthogonally in order to have an effective lateral segmentation of 5 by 5 millimetres. Each strip is read out by a multi-pixel photon counter (MPPC), a kind of pixelated photon detector.
A scintillator strip with a multi-pixel photon counter (and a coin for size comparison).
The ScECAL in the test beam at DESY was the first step of the technological prototype, so it didn’t have multiple layers. Instead, the team changed the number of absorber layers to make “pseudo multi-layers”, and the plots show energy deposits by electron showers in the pseudo first layer and the pseudo ninth layer. The CALICE group has already tested and confirmed good performance of the ScECAL with a physics prototype, so as the next stage, the ScECAL group is developing a technological prototype, where the readout electronics is squeezed in between each layer to build a realistic ECAL for the ILC. “We have learned many things from this test beam to go to the next step,” says Katsushige Kotera from the CALICE ScECAL group. After initial difficulties, the team had decided to extend data taking by a week, and then everything fell into place – their understanding of the detector as well as handling the beam properties. It’s not only the success, but also those difficult days in the beginning that are a valuable experience, says Kotera. “The students struggled hard with me from the beginning until the end. I believe that they succeeded to get one grade higher through this experience.”
The technological prototype of the ScECAL is developed by not only the ScECAL group but in close collaboration with the Analog HCAL group and the Silicon-tungesten ECAL group together as a collaboration from all over the world.
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