BEGe Detector studies update

Transcription

1 BEGe Detector studies update Performance and analysis Dušan Budjáš Stefan Schönert Mikael Hult* MPI für Kernphysik Heidelberg * IRMM Geel MAX-PLANCK-INSTITUTNSTITUT FÜR KERNPHYSIK

2 Outline 1. BEGe publication 2. BEGe pulse-shape shape discrimination method 3. Update on recent results 4. Summary/Outlook 2

3 BEGe publication submitted to JINST accepted for publication after some minor corrections ArXiv: [nucl-ex] Contents: charge collection performance and stability PSD method and its calibration validation via coincident SCS and collimated 2.6 MeV beam experimental PSD results also: proceedings from CIPANP 29 (4 pages, submitted to AIP) previously: IEEE 28 proceedings arxiv: v1[nucl-ex] 3

4 +HV e BEGe pulse shape discrimination method h + read-out Ramo's theorem I W W W(x) Ew(x) BEGe (hypothetical) distance from the read-out electrode, x [cm] True coaxial W(r) Ew(r) r [cm] ( ) e ( e ) h ( h t = q E x ( t) v+ q E x ( t) ) v W W Ew [cm -1 ] Ew [cm -1 ] ref: Knoll 4

5 +HV e BEGe pulse shape discrimination method h + read-out W W(x) Ew(x) BEGe (hypothetical) distance from the read-out electrode, x [cm] Ew [cm -1 ] Current [a. u.] Interaction point distance from read-out electrode [mm]: Amplitude [a.u.] Time [ns] I ( ) e ( e ) h ( h t = q E x ( t) v+ q E x ( t) ) v W Time after trigger [ns] simplified 1-dimensional calculation real recorded signal Ramo's theorem W 5

6 Current [a. u.] +HV e BEGe pulse shape discrimination method single site multi site h + read-out I energy normalised Time [ns] W W(x) Ew(x) BEGe (hypothetical) distance from the read-out electrode, x [cm] ( ) e ( e ) h ( h t = q E x ( t) v+ q E x ( t) ) v W Amplitude [a.u.] ~equal event energy Time after trigger [ns] simplified 1-dimensional calculation real recorded signal Ramo's theorem A W A Ew [cm -1 ] 6

7 PSD parameter distribution DEP kev FEP kev SEP kev FEP kev DEP events SSE band accepted rejected FEP kev MSE region SEP FEP kev 7

8 PSD calibration <A/E> m SSE Number of counts fit residuals Energy [kev] 14 Compton ± 25 kev Th Compton 2245 ± 25 kev DEP ± 1 σ fitted DEP curve.336 MSE exponential tail SSE Gaussian.333 fit function x 1-4 <A/E> SSE Energy [kev] A/E [a.u.] 8

9 PSD calibration <A/E> m SSE fit residuals Energy [kev] fitted curve x Energy [kev] 9

10 PSD calibration 228 Th 2 σ Assuming gaussian distribution (resolution dominated by noise): 2 σ 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 1

11 Updated experimental results cut at 2 σ from the SSE band mean simplified MC estimation of νββ acceptance: (89.4 ± 1.4)% 1% νββ γ-lines 1% 1%.1% CC = Compton continuum (239 ± 35 kev) 11

12 PSD validation via coincident single-compton scattering A/E parameter histograms: no effect of event topology or spatial distribution SCS double-escape peak (DEP) is a good representation of ββ events validated our PSD calibration using DEP and Compton continuum events corrected for energy dependence from Compton cont. 12

13 PSD performance in dependence on spatial event distribution SSE band SSE linenear-electrode events accepted 1 2 rejected MSE region Interaction point distance from read-out electrode [mm]: e Current [a. u.] h Time [ns] 13

14 PSD performance in dependence on spatial event distribution 228 Th source 6 mm collimated beam DEP reject accept amplified current amplitude A e h + acceptance: DEP 1621 kev uncollimated: 89% 1% collimated (centre): 88% 23% 14

15 HV dependence of PSD performance Fraction of events above SSE band. 35% 3% 25% 2% 15% 1% 5% electrode extent beam size 4V 3s 425V 3s 45V 3s 375V 3s % Collimator distance from centre [mm] e < 3% of total volume PSD ineffective Complementary PSD techniques effective also in this region (e.g. rise-time based) h + the extent of the insensitive region grows with HV 15

16 PSD performance in dependence on crystal size PSD tested on 6 cm BEGe (at IRMM Geel, Belgium) results: SEP survival 9.2% ( 8 cm: 7.1%) FEP survival 13.5% ( 8 cm: 1.2%) at 89% DEP acceptance Th spectrum after 2 σ PSD cut 6 5 γ 1588 kev DEP 4 γ 1621 kev

17 PSD performance in dependence on crystal size PSD tested on 6 cm BEGe (at IRMM Geel, Belgium) results: SEP survival 9.2% ( 8 cm: 7.1%) FEP survival 13.5% ( 8 cm: 1.2%) at 89% DEP acceptance 1% DEP survival probability 1% γ 1588 kev γ 2615 kev γ 1621 kev SEP 228-Th with MPIK BEGe (8 cm); 3.8 kv 232-Th with IRMM BEGe (6 cm); 3.5 kv 232-Th with IRMM BEGe (6 cm); 3.1 kv 1% Energy [kev] 17

18 Summary and conclusions PSD validated with SSE events of different topology (DEP vs. SCS), spatial distribution, and energy discovered < 3% loss of MSE rejection sensitivity near the read-out electrode (specific to our PSD method) no spatial dependence of SSE acceptance found no change of PSD sensitivity in dependence on HV (except for a slight growth of the MSE-insensitive volume) PSD performance in smaller crystals likely different only due to lower γ-ray absorption efficiency 18

19 Outlook tests of FE electronics for bare BEGe operation in LAr optimisation of the PSD procedure and coordination with LNGS BEGe team in advance of acceptance testing of new BEGe's from dep Ge coordination with Zürich group (Francis) on definition of the Phase 2 calibration source from the point of view of PSD calibration requirements 19

20 Backup slides 2

21 16 14 HV scan 1.33 MeV (Co-6) FWHM [kev] MeV (pulser) High voltage [V] FWHM kev HV 21

22 HV scan Number Number of counts of [per 6 s] MeV peak intensity 1.33 MeV peak position High voltage [V] counts Peak position [channel] peak intensity peak position channel V 22

23 Dušan Dušan Budjáš Budjáš MPIK Heidelberg Charge collection characterisation peak position FWHM Am scan gain variation: % peak position FWHM gain variation: % 1 2 distance from center [mm] d d FWHM [kev] peak position [kev] distance from the top of crystal, d [mm] FWHM [kev] peak position [kev] collimated kev active mass: 836 g (95 % of total mass) dead layer:.43 mm 23

24 Charge collection losses: peak tails Co-6 (high rate) Co-6 (high rate+pile-up reject) Co-6 (low rate) Number of counts Energy [kev] 24

25 Charge collection stability.15% Relative peak position corrected for pulser fluctuation.1%.5%.% -.5% -.1% -.15% 1333 kev 1174 kev LN refilling weekends 1 st set 2 nd set Setup rearrangement -.2% Date Maximal variation:.15% kev 25

26 Dušan Budjáš Charge collection stability: count rate Counts per 3 hr kev 1333 kev Counts per 3 hr (corrected) Days since

27 Coincident recording Preamp no shaping MPIK Pb/Cu shield 23.6 cm 228 Th source (no collimator) solid angle: ~ 1 Canberra 22CSL 25 cm - 8 cm TFA Canberra 2111 MPIK no shaping Amplified raw signal Time- filtered signal (1 ns differentiation and 1 ns integration time) Amplified raw signal Struck SIS 331 flash- ADC 14- bit, 1 MHz pulse recording, digital shaping (τ shaping = 1 µs) 1.6 µs coincidence window software gate 27

28 HV dependence of PSD performance current signal amplitude grows with HV => weighing field shape changes (the width of the SSE band seems to slightly increase with HV).32.3 <A/E>sse V sigma(a/e_sse)