A high-resolution CMOS imaging detector for the search of neutrinoless double decay in 82Se

International School of Subnuclear Physics55th Course: Highlights from LHC and the other frontiers of physicsJun/18/2017

Xinran LiDepartment of Physics, Princeton University

Chavarria, A. E., C. Galbiati, X. Li, and J. A. Rowlands. Journal of Instrumentation 12, no. 03 (2017): P03022.

Neutrinoless double decay (0 ) 2 :

0 :

Half-life of 0

Phase space factor Nuclear matrix element Effective Majorana mass

➢ Neutrinos are Majorana particles➢ Explicit violation of lepton number➢ Indication of neutrino mass

⬆ Possible values of axial coupling constant

Predictions on from oscillations as a function of the lightest neutrino mass and combined experimental limit from 136Xe ➡arXiv:1601.07512 [hep-ph]

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https://arxiv.org/abs/1601.07512https://arxiv.org/abs/1601.07512

Selenium82Se is a good candidate for the search of 0

- High . Large phase space and low background

- Long 2 life time

- Relatively highabundance

LUCIFER: ZnSeAdvances in High Energy Physics 2013 (2013).

SuperNEMO: Tracking ChamberThe European Physical Journal C-Particles and Fields 70.4 (2010): 927-943.

X. Li Princeton University Erice 2017 3arXiv:1601.07512 [hep-ph]

https://arxiv.org/abs/1601.07512https://arxiv.org/abs/1601.07512

Conceptual designAmorphous 82Se deposits on CMOS arrays. Long exposure O(10s)

“Background free” :

- Compact and modular design, easy to scale up- Fine energy resolution- Low background + track geometry discrimination

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Selenium X-ray plate detector

Se X-ray detectors are used in medical imaging. (e.g. 720 cm2, 1 mm thick, 85 um pixel size.)

Large band gap, negligible dark current at room temperature. Bias voltage ~20V/um.

Replace current TFT pixel array to CMOS pixel array to achieve < 100 e-h/pixel noiseOperating at very low read out rate.

Current Applied Physics 6.3 (2006): 288-292

CMOS active pixel array

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Particle track imaging

and (right: an example from silicon CCD ) stopping power

Double beta

Track reconstruction acceptanceDouble Image of charge Imager z

Single Image of charge Imager z

15um x 15um 200um/layer

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Energy resolution

a-Se, CMOS, dead layer

Fano factor = 0.6 (Intrinsic value = 0.03~0.06)e-h recombination reduces Fano factor.Darbandi, A., et al. Journal of Physics: Condensed Matter 24.45 (2012): 455502.

W = 15eV/ehp

Higher energy beta has lower ionization density -> lower recombination and higher energy resolution

Experiments on going.

NIST ESTAR

J. Appl. Phys., Vol. 85, No. 11, 1 June 1999

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Simulated double beta decay spectrum.

Expected energy resolution at : FWHM = 24 keV Simulated single rate in ROI =

2 background in ROI =

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Simulation result of mββ = 1 meV and a strongly quenched nucleon axial coupling constant

Background estimationOnly tracks which total energy falls in ROI are regard as background.

from decay chain 238U, 232Th:- Se: < 110 Bq/kg LUCIFER, Eur. Phys. J. C 75 (Dec.,2015) 591–597.

- CMOS array: < 0.01 Bq/cm2 - Surface 210Po: < 0.1 Bq/cm2DAMIC, JINST 10 (Aug., 2015) P08014.

- Cosmogenic 83Se: < 0.02 μBq/kg 78,80,81,82As: < 0.3 nBq/kg

EXO, JCAP 1308 (Aug.,2013) 049.EXO, JCAP 2016 (Apr., 2016) 029.

with energy > ROI: - ( ,n) reaction- Cosmogenic 56Co: < 0.02 μBq/kgLUCIFER, Eur. Phys. J. C 76 (July, 2016) 364.

Only parents with decay in ROI

Rejected by decay chain

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Background rejection

- Multi-tracks with same vertex- Spatial correlation - Discrimination of single and double track

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Conclusion

Advantages: - modular design, compactness and simplicity in operation- modest radio-purity requirements — which relies on high resolution imaging and the choice of 82Se- scalability of the technology — which relies on widespread fabrication processes in the semiconductor industry

Experimental demonstration of the predicted performance is on going.

The predicted signal and background rate, assuming = 1 meV

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Outlook

Magnetic field:Simulation with 20T magnetic field

Track reconstruction algorithm:-ray and more complex topology

Single atom counting of 82Krpixel

vertexBragg peaks

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