A tracker for the Mu3e experiment based on high-voltage monolithic active pixel sensors

Abstract

The Mu3e experiment searches for the lepton flavour violating decay µ + → e + e − e + , aiming for a branching fraction sensitivity of 10 −16 . This requires an excellent momentum resolution for low energy electrons, high rate capability and a large acceptance. In order to minimize multiple scattering, the amount of material has to be as small as possible. These challenges can be met with a tracker built from high-voltage monolithic active pixel sensors (HV-MAPS), which can be thinned to 50 µm and which incorporate the complete read-out electronics on the sensor chip. To further minimise material, the sensors are supported by a mechanical structure built from 25 µm thick Kapton foil and cooled with gaseous helium.

The quest for $$\mu \rightarrow e \gamma $$ μ → e γ and its experimental limiting factors at future high intensity muon beams

“…The detector technology adopted for a tracking approach is therefore relevant: while gaseous detectors have been the choice for both MEGA and MEG, a silicon vertex tracker is used for the search of μ + → e + e + e − by the Mu3e Col- laboration [20], and a similar design has been suggested for future μ + → e + γ searches [16]. State-of-the-art silicon pixel detectors can reach very good position resolutions (∼ 3 µm), with a thickness of 50 µm Si + 25 µm Kapton per layer [21], corresponding to ∼ 10 −3 radiation lengths per layer.…”

Charged lepton flavour violation searches at the Paul Scherrer Institut: Status of the MEGII and Mu3e experiments

“…The particle momenta will be measured using a novel tracker, made of silicon devices (High-Voltage Monolithic Active Pixel, HV-MAPS [61][62][63]) for a momentum resolution of about 300 keV/c over most of the detector acceptance and momentum range, a vertex resolution of ≈ 200 µm and a relative fast response O(10) ns. The HV-MAPs have the unique characteristics of integrating the active sensor and the readout in the same device.…”

Technology Needs for Modular Pixel Detectors

“…One way to achieve a fully depleted detector is to exploit the characteristics of the high-voltage complementary metal-oxide semiconductor (HVCMOS) processes that are normally used for automotive applications (Figure 10.18) [68][69][70][71][72][73][74]. Radiation hardness and a good signal/noise ratio are very important characteristics to be considered.…”

“…Using the HVCMOS process [68][69][70][71][72][73][74], it is possible to design the entire pixel inside the deep n-well that is used to collect the charge. The main advantages of this are increased radiation tolerance to nonionizing damage and the possibility to have in-pixel electronics.…”