Development of a Tracking Detector for the Mu3e-Experiment based on novel thin High-Voltage Monolithic Active Pixel Sensors
Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Final Report Abstract
For the new Mu3e particle physics experiment at the Paul-Scherrer Institute in Switzerland a pixel detector based on a commercial high-voltage CMOS process has been developed. The Mu3e experiment will search for the rare decay of a positively charged muon into two positrons and one electron. This decay violates a quantum number known as lepton flavor and is in the Standard Model (SM) of particle physics suppressed by 54 orders of magnitude compared to the ordinary muon decay into one positron and two neutrinos. In many models beyond the SM this decay is largely enhanced and expected at observable rates, thus motivating a dedicated search for it. The current experimental limit is B(µ+ → e+ e+ e− )< 10^−12 at 90% confidence level and the Mu3e experiment is aiming to improve the sensitivity more than two orders of magnitude in the first, and by about four orders of magnitude in the second phase. To reach the aimed sensitivity, the experiment has to provide high precision particle tracking at large muon decay rates (≥ 108 /s). This can be realized by a high-resolution pixel detector with four tracking layers with a spatial resolution of about 20 µm and a time resolution for single hits of better than 20 ns. The pixel detector has to be capable to cope with high rates and must implement a continuous readout of all hits for real time track reconstruction. The pixel sensor as well as the pixel tracker mechanics and supports have to be extremely thin to avoid multiple coulomb scattering of particles. For the same reason a gaseous helium cooling system has to implemented to cool the frontend-electronics and the pixel sensors. The severe requirements on the pixel detector material are fulfilled by monolithic active pixel sensors (MAPS) which integrate sensing, digitization and readout in the same silicon die and can be produced with a thickness of only 50 µm. The usage of an HV-CMOS process ensures a fast charge collection and provides an excellent time resolution of about 5 ns second. A 1 × 2 cm^2 -sized prototype sensor (Mupix8) was developed which fulfills all requirements of the experiment. A positive surprise is the relatively high radiation tolerance of the used 180 nm HV-CMOS process, making it very attractive to use this technology also for other applications in harsh radiation environmments, for example at the Large Hadron Collider at CERN. Within this project, a detailed technical concept for the Mu3e pixel detector has been developed based on an ultra-light pixel module design. The modules consist of 50 µm thin, monolithic Mupix sensors and special high-density interconnets, composed of aluminium for power and readout and polyimide for mechanical support. A gaseous helium cooling system was studied in detail using simulations as well as experimental tests with thermo-mechanical mockups. The Mu3e pixel detector layers have a total thickness of only 1.15 of radiation length per layer, much less than any other particle physics pixel detector.
Publications
- MuPix7 - A fast monolithic HV-CMOS pixel chip for Mu3e, JINST 11 (2016) 1, C11029
H. Augustin et al.
(See online at https://doi.org/10.1088/1748-0221/11/11/C11029) - Ultra-low material pixel layers for the Mu3e experiment, JINST 11 (2016) no.12, C12006
N. Berger et al.
(See online at https://doi.org/10.1088/1748-0221/11/12/C12006) - MuPix8 - A large-area HV-MAPS chip, PoS (Vertex 2017) 057
H. Augustin et al.
(See online at https://doi.org/10.22323/1.309.0057) - Status of HVCMOS developments for ATLAS, JINST 12 (2017) C02030
I. Perić et al.
(See online at https://doi.org/10.1088/1748-0221/12/02/C02030) - The MuPix System-on-Chip for the Mu3e Experiment, Nucl. Instrum. Meth. A845 (2017) 194
H. Augustin et al.
(See online at https://doi.org/10.1016/j.nima.2016.06.095) - The MuPix Telescope: A Thin, high Rate Tracking Telescope, JINST 12 (2017) C01087
H. Augustin et al.
(See online at https://doi.org/10.1088/1748-0221/12/01/C01087) - Efficiency and timing performance of the MuPix7 highvoltage monolithic active pixel sensors, Nucl. Instrum. Meth. A902 (2018) 158
H. Augustin et al.
(See online at https://doi.org/10.1016/j.nima.2018.06.049) - Irradiation study of a fully monolithic HV-CMOS pixel sensor design in AMS 180nm, NIM A905 (2018) 53
H. Augustin et al.
(See online at https://doi.org/10.1016/j.nima.2018.07.044) - MuPix8 - Large area monolithic HVCMOS pixel detector for the Mu3e experiment
H. Augustin et al.
(See online at https://doi.org/10.1016/j.nima.2018.09.095)
