The Belle-II Electromagnetic Calorimeter Endcap

点击翻译按钮获取中文摘要

Belle-II will probe the flavour sector of particle physics at the high-luminosity SuperKEKB e+e- collider, located at the KEK laboratory in Japan. Physics operations will start in late 2016, with the goal of collecting by 2022 thirty times the combined integrated luminosity of the two previous generation B-factories, PEP-II at SLAC and KEKB at KEK. This precision-frontier facility will open an exciting window on new energy scales beyond the reach of existing colliders, including the LHC, by virtue of quantum loop corrections that are sensitive to massive, and as yet undiscovered, particles. These hypothesized particles manifest themselves in precision measurements of processes involving bottom and charm quarks and tau leptons, such as CP violation and other asymmetries, rare decays, and processes that are forbidden within our current understanding of physics. This program is complementary to direct searches for new physics at the LHC. The funds requested will enable the Canadian group to finalize the research needed for the group's detector hardware contribution, and to develop the tools and expertise for the full hardware contribution. Belle-II will start data taking with the thallium-doped cesium iodide (CsI(Tl)) scintillator calorimeter from Belle, outfitted with new digitizing and feature-extraction electronics. This calorimeter had very good performance, but has a slow scintillation time constant (1 microsecond). At the increased luminosity of SuperKEKB, high occupancies from beam related backgrounds will cause significant deterioration of the performance of the forward endcap calorimeter. As its contribution to the Belle-II detector, the Canadian group is proposing to upgrade the high-occupancy regions of the forward endcap to pure CsI. Pure CsI is much faster than CsI(Tl), and is therefore much less sensitive to backgrounds. However, it has a much lower light yield. To deal with the characteristics of fast pulses, low light yield and large dynamic range, the CsI crystals will use different photosensors, amplifiers, digitizers, and feature-extraction algorithms than the existing calorimeter. The Canadian group will take responsibility for all aspects of this project, including procuring the crystals and photomultiplier tubes; developing and building the amplifiers, digitizing, and feature-extraction electronics; calibration systems and procedures; and modifications to the mechanical and cooling systems. We are requesting funds to develop and test a 25-crystal array together with the associated photosensors and electronics, approximately 8% of the full project. This will allow us to complete the R&D on the readout system, and verify that our proposed solutions satisfy the requirements at a system level in a test beam environment. It will also allow us to develop the crystal and phototube procurement protocols, including the equipment and tooling needed to verify the specifications. Understanding the beam-related backgrounds is an essential component of the project. Belle-II is developing a set of detectors to be installed in January 2015, which will quantify the backgrounds during the commissioning of SuperKEKB and enable comparisons to simulations. We have proposed to the collaboration that this set should include thermal neutron detectors, since this background component determines the lifetime of the existing calorimeter readout electronics, as well as that of other Belle-II detector systems, and is responsible for a noticeable component of the calorimeter occupancy. It is also the most difficult component to simulate accurately. We are requesting funds for He-3 neutron counters to undertake this measurement.