The Potential of Hybrid Pixel Detectors in the Search for the Neutrinoless Double-Beta Decay of¹¹⁶Cd

Abstract

We investigated the potential of the energy resolving hybrid pixel detector Timepix contacted to a CdTe sensor layer for the search for the neutrinoless double-beta decay ofCd. We found that a CdTe sensor layer with 3 mm thickness and 165 μm pixel pitch is optimal with respect to the effective Majorana neutrino mass (mββ) sensitivity. In simulations, we were able to demonstrate a possible reduction of the background level caused by single electrons by approximately 75% at a specific background rate of 10−3counts/(kg×keV×yr) at a detection efficiency reduction of about 23% with track analysis employing random decision forests. Exploitation of the imaging properties with track analysis leads to an improvement in sensitivity tomββby about 22%. After 5 years of measuring time, the sensitivity tomββof a 420 kg CdTe experiment (90%Cdenrichment) would be 59 meV on a 90% confidence level for a specific single-electron background rate of 10−3counts/(kg×keV×yr). Theα-particle background can be suppressed by at least about six orders of magnitude. The benefit of the hybrid pixel detector technology might be increased significantly if drift-time difference measurements would allow reconstruction of tracks in three dimensions.

Improvement of the energy resolution of pixelated CdTe detectors for applications in 0νββsearches

“…We already showed that alpha particle background can be reduced by at least a factor of 4.32 • 10 5 with a 0νβ β signal loss of less than 4.5% [9]. Single electron background can be rejected by 75% with a signal loss of about 25% [10]. While a thick sensor increases the detection efficiency, it also has a negative influence on the energy resolution.…”

“…While a thick sensor increases the detection efficiency, it also has a negative influence on the energy resolution. We showed that with the current Timepix, the detectors should optimally have a thickness of about 3 mm [10]. So compared to monolithic coplanar grid detectors a lot more detectors are required to obtain the same nuclide mass, which translates to higher cost, higher energy consumption, more channels to read out and calibrate and more background since the mass to surface ratio is less favourable.…”

Current Status and Future Perspectives of the COBRA Experiment

“…COBRA is also exploring the use of pixelized detectors, which have the potential to further reduce the background using topological information. These efforts are not considered in this paper but are discussed in [5].…”

3D reconstruction of particle tracks in a 2 mm thick CdTe hybrid pixel detector

“…Such applications include space weather analyses [7], the determination of trapped particle directions in the Van-Allen radiation belts [8,9], monitoring of secondary radiation in hadron therapy [10], the study of the antiproton annihilation [4] and electron microscopy [11]. Especially, when equipped with CdTe or CdZnTe as sensor material Timepix detectors can be investigated for double beta decay experiments [12]. All of the above applications would profit significantly from a determination of the interaction depth in the sensor by improving particle discrimination, background event suppression, annihilation vertex reconstruction, impact angle or impact point determination.…”