Searching for charged lepton flavour violation with the Mu3e experiment -- Pixel Sensor

MU3E第一阶段实验的主要目标是寻找违反衰变伽马-gt；e的带电轻子味道，灵敏度为bR(伽马-gt；e e e)&lt；5×10−15，置信度为90%，与现有界限相比，相应地提高了200倍。需要高精度的跟踪来抑制高达每秒10^8的介子停止速率的大背景。电子的位置和动量将通过一个四层像素跟踪探测器(PTD)来测量，该探测器利用高压CMOS单片有源传感器(HV-MAP)。高的背景速率决定了对跟踪探测器系统和像素传感器的要求。像素传感器必须提供高位置分辨率、良好的时间分辨率、低功耗和高速率能力。此外，像素传感器应该尽可能薄，因为厚度决定了探测器中多次库仑散射量和Bhabha散射率。为了进行Mu3e实验，一种专用的HV-MAP传感器，MuPix已经开发了多年。MuPix是一款集成了片上数字读出的全单片传感器。MuPix传感器已接近生产就绪，最终传感器的生产、鉴定、调试和校准是PIX项目的主要主题。

The main goal of the Mu3e Phase I experiment is the search for the charged lepton flavor violating decay gamma -> e e e with a sensitivity of BR(gamma -> e e e)< 5 × 10−15 at 90% confidence level (CL), corresponding to a factor 200 improvement compared to the existing bound. High precision tracking is required to suppress the large background for muon stopping rates up to 10^8 muons per second. The position and momentum of electrons will be measured by means of a four layer pixel tracking detector (PTD) which exploits High-Voltage CMOS Monolithic Active Sensors (HV-MAPS). The high rate of background determines the requirements on the tracking detector system and the pixel sensor. The pixel sensor has to provide high position resolution, good time resolution, low power consumption and high rate capability. In addition, the pixel sensor should be as thin as possible since the thickness determines the amount of multiple Coulomb scattering in the detector and also the rate of Bhabha scattering.For the Mu3e experiment, a dedicated HV-MAPS sensor, the MuPix has been developed over many years. MuPix is a fully monolithic sensor which integrates on-chip digital readout. The MuPix sensor is close to production readiness and the production, qualification, commissioning and calibration of final sensor is main subject of the PIX project.