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Study on BEGe detectors for 0nbb search, optimized for signal processing efficiency, energy resolution, and low noise levels. Analysis of front-end bandwidth constraints for enhanced performance using pulse-shape discrimination methods.
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MAX-PLANCK-INSTITUTFÜR KERNPHYSIK 1. BEGe Detectors2. Constraints on FE bandwidth Dušan Budjáš MPI für Kernphysik • Heidelberg
Dušan Budjáš MPIK Heidelberg n+ contact (+HV) p-type germanium mass: 878 g p+ contact (read-out) Modified-electrode detectors for 0nbb search • Majorana collaboration: p-type point-contact detectors • have excellentMSE / SSE discrimination performance • avoid external background from multiple contacts • also: excellent energy resolution and low-energy threshold Standard commercial detectors with similar features: BEGe (Broad Energy Ge detector) from Canberra • research program within GERDA collaboration P.S. Barbeau, J.I. Collar and O. Tench JCAP 0709:009,2007 (Crystal mass: 475 g) 81 × 32 mm BE5030 2
Dušan Budjáš MPIK Heidelberg f 81 mm n+ contact 32 mm p-type germanium p+ contact Broad-energy Ge-detector • covers energy range 3 keV - 3 MeV • enhanced efficiency for low-energy gammas • low capacitance ( low noise) Specifications: depletion voltage 4000 V FWHM @ 122 keV 0.63 keV FWHM @ 1.33 MeV 1.8 keV mass 870 g 3
Dušan Budjáš MPIK Heidelberg Energy resolution Struck SIS 3301 flash-ADC with 14-bit resolution,100 MHz sampling rate, digital shaping 4
Dušan Budjáš MPIK Heidelberg energy normalised ~equal event energy BEGe pulse shape discrimination method +HV BEGe (hypothetical) e− h+ read-out A A True coaxial simplified 1-dimensional calculation real recorded signal ref: Knoll Ramo's theorem 5
Dušan Budjáš MPIK Heidelberg Experimental results 100% 10% 1% 0.1% g-lines CC = Compton continuum (2039 ± 35 keV) 6
BEGelow-mass holder mounting signal cable
Constraints on front-end bandwidth from the point of view of BEGeA/E pulse-shape discrimination method(simplified study)
Dušan Budjáš MPIK Heidelberg Test of PSD performance in dependence on signal bandwidth • off-line modification of recorded experimental pulse-shape data • step 1: FE bandwidth restriction simulated by various filter methods raw FADC data (pulser signal) after digital filtering 24 ns 40 ns – 500 ns 9
Dušan Budjáš MPIK Heidelberg • step 2: PSD on filtered pulses (DEP acceptance always at 90%) 102 101.5 101 100.5 3000 2000 1000 DEP (fixed 90% acceptance) 228Th A A 1621 keV Counts Energy [keV] 10
Dušan Budjáš MPIK Heidelberg PSD performance in dependence on applied shaping 228Th Modified FE 11
Dušan Budjáš MPIK Heidelberg PSD performance in dependence on applied shaping 228Th Modified FE 12
Dušan Budjáš MPIK Heidelberg PSD performance in dependence on applied shaping Modified FE longer shaping times improve PSD rejection of 60Co background 13
Dušan Budjáš Summary and conclusions • BEGe technology: standard p-type det. tech. single read-out per det., Phase-1 type holder • dependence of PSD performance on FE rise-time simulated by applying shaping filters to recorded experimental data • PSD requirements on front-end bandwidth not very demanding: ~100 ns rise-time sufficient • more accurate study can be performed using pulse-shape simulation 14
Dušan Budjáš Backup slides 15
Dušan Budjáš MPIK Heidelberg n+ contact (+HV) p-type germanium mass: 878 g p+ contact (read-out) Modified-electrode detectors for 0nbb search • Majorana collaboration: p-type point-contact detectors • have excellentMSE / SSE discrimination performance • avoid external background from multiple contacts • also: excellent energy resolution and low-energy threshold Standard commercial detectors with similar features: BEGe (Broad Energy Ge detector) from Canberra • research program within GERDA collaboration P.S. Barbeau, J.I. Collar and O. Tench JCAP 0709:009,2007 (Crystal mass: 475 g) 81 × 32 mm BE5030 16
Dušan Budjáš MPIK Heidelberg f 81 mm n+ contact 32 mm p-type germanium p+ contact Broad-energy Ge-detector • covers energy range 3 keV - 3 MeV • enhanced efficiency for low-energy gammas • low capacitance ( low noise) Specifications: depletion voltage 4000 V FWHM @ 122 keV 0.63 keV FWHM @ 1.33 MeV 1.8 keV mass 870 g 17
Dušan Budjáš MPIK Heidelberg Energy resolution Struck SIS 3301 flash-ADC with 14-bit resolution,100 MHz sampling rate, digital shaping 18
Dušan Budjáš MPIK Heidelberg energy normalised ~equal event energy BEGe pulse shape discrimination method +HV BEGe (hypothetical) e− h+ read-out A A True coaxial simplified 1-dimensional calculation real recorded signal ref: Knoll Ramo's theorem 19
Dušan Budjáš PSD parameter distribution MPIK Heidelberg FEP1620.7 keV DEP1592.5 keV FEP2614.5 keV SEP2103.5 keV DEP events SSE band accepted rejected MSE region FEP2614.5 keV FEP1620.7 keV SEP 20
Dušan Budjáš MPIK Heidelberg MSE SSE 2 s PSD calibration 228Th Assuming gaussian distribution (resolution dominated by noise): 2 s 97.7% SSE acceptance arbitrary choice of "SSE identification probability" SSE defined as events with charge cluster extent so small that the electric field doesn't change significantly across it's width 21
Dušan Budjáš MPIK Heidelberg Experimental results • cut at 2 s from the SSE band mean 100% 10% 1% 0.1% g-lines CC = Compton continuum (2039 ± 35 keV) 22
Dušan Budjáš MPIK Heidelberg moving-average smoothing smoothing span [points]: 5, 7, 9, 13, 17 ... amplitude t [ns]
Dušan Budjáš MPIK Heidelberg smoothing via local regression using weigthed least squares smoothing span [points]: 9, 11, 13, 15, 17, 19, 21, 23, ... amplitude t [ns]
Dušan Budjáš MPIK Heidelberg IIR Butterworth filter, 12 dB drop pass-band frequency [MHz]: 8 7 6 5 4 3 2 1 0.5 amplitude t [10 ns]
Dušan Budjáš MPIK Heidelberg IIR Butterworth filter, 24 dB drop pass-band frequency [MHz]: 8 7 6 5 4 3 2 1 amplitude t [10 ns]
