Simulation and modeling of BEGe detectors for GERDA Phase II

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1 Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini, M. Barnabé Heider, E. Bellotti, D. Budjáš, C. Cattadori, A. di Vacri, A. Garfagnini, L. Pandola, S. Schönert and C. A. Ur Max-Plank-Institute für Kernphysik DPG, March 15th 2010 Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 1

2 Outline 1 The BEGe detectors 2 The simulation 3 BEGe modeling and Pulse Shape Discrimination (PSD) features 4 PSD performances for external and internal background 5 Conclusion Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 2

3 The BEGe detectors The BEGe geometry thick-window Al endcap mm mm p-type Ge n+ contact 3500 V groove p+ contact (diameter 10 mm) 0 V electrode and groove not to scale Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 3

4 The simulation The structure of the simulation I. MC simulation > coordinates and energy of the hits II. Signal formation and development < coordinate of each hit > electron and hole trajectories > the signal induced on the point size electrode III. DAQ simulations < energy and signal for each hit in an event < the Preamplifier Transfer Function (PTF) > each pulse is convolved with the PTF > all the pulses of an event are added up > the noise is added to the total pulse Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 4

5 The simulation The structure of the simulation I. MC simulation > coordinates and energy of the hits interaction points anode cathode II. Signal formation and development < coordinate of each hit > electron and hole trajectories > the signal induced on the point size electrode III. DAQ simulations < energy and signal for each hit in an event < the Preamplifier Transfer Function (PTF) > each pulse is convolved with the PTF > all the pulses of an event are added up > the noise is added to the total pulse Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 4

6 The simulation The structure of the simulation I. MC simulation > coordinates and energy of the hits anode cathode electrons holes II. Signal formation and development < coordinate of each hit > electron and hole trajectories > the signal induced on the point size electrode III. DAQ simulations < energy and signal for each hit in an event < the Preamplifier Transfer Function (PTF) > each pulse is convolved with the PTF > all the pulses of an event are added up > the noise is added to the total pulse Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 4

7 The simulation The structure of the simulation I. MC simulation > coordinates and energy of the hits anode cathode electrons holes II. Signal formation and development < coordinate of each hit > electron and hole trajectories > the signal induced on the point size electrode e pulse h pulse total pulse III. DAQ simulations < energy and signal for each hit in an event < the Preamplifier Transfer Function (PTF) > each pulse is convolved with the PTF > all the pulses of an event are added up > the noise is added to the total pulse adc counts e-08 1e e-07 2e e-07 3e e-07 4e e-07 time [ns] Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 4

8 The simulation The structure of the simulation I. MC simulation > coordinates and energy of the hits anode cathode electrons holes II. Signal formation and development < coordinate of each hit > electron and hole trajectories > the signal induced on the point size electrode e pulse h pulse total pulse total pulse + pre III. DAQ simulations < energy and signal for each hit in an event < the Preamplifier Transfer Function (PTF) > each pulse is convolved with the PTF > all the pulses of an event are added up > the noise is added to the total pulse adc counts e-08 1e e-07 2e e-07 3e e-07 4e e-07 time [ns] Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 4

9 The simulation The structure of the simulation I. MC simulation > coordinates and energy of the hits anode cathode electrons holes II. Signal formation and development < coordinate of each hit > electron and hole trajectories > the signal induced on the point size electrode MeV MSE 1.1 MeV SSE (28,34,16) 0.4 MeV SSE (46,34,26) 0.5 MeV SSE (66,34,26) III. DAQ simulations < energy and signal for each hit in an event < the Preamplifier Transfer Function (PTF) > each pulse is convolved with the PTF > all the pulses of an event are added up > the noise is added to the total pulse adc counts [a.u.] e-07 2e-07 3e-07 4e-07 5e-07 6e-07 7e-07 8e-07 9e-07 time [s] Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 4

10 The simulation The structure of the simulation I. MC simulation > coordinates and energy of the hits anode cathode electrons holes II. Signal formation and development < coordinate of each hit > electron and hole trajectories > the signal induced on the point size electrode MeV MSE 1.1 MeV SSE (28,34,16) 0.4 MeV SSE (46,34,26) 0.5 MeV SSE (66,34,26) III. DAQ simulations < energy and signal for each hit in an event < the Preamplifier Transfer Function (PTF) > each pulse is convolved with the PTF > all the pulses of an event are added up > the noise is added to the total pulse adc counts [a.u.] e-07 2e-07 3e-07 4e-07 5e-07 6e-07 7e-07 8e-07 9e-07 time [s] Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 4

11 The simulation Validation of the PSS The validation was carried out by comparing directly the simulated and the experimental signals: 241 Am collimated source well localized events close to the detector surface; charge [a.u.] charge [a.u.] exp sim time [sample] time [sample] exp sim Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 5

12 BEGe modeling and PSD features BEGE Charge-signal development The charge signal is provided by the Shockley-Ramo: Q(t) = qφ w(r(t)) where r(t) is the position of the charge bunch q at the time t and φ w(r(t)) is the weighting potential (defined as as the electric potential calculated when the considered electrode is kept at a unit potential, all other electrodes are grounded and all charges inside the device are removed) adc counts [a.u.] time [s] The signal grows slowly at the beginning when the charges are far from the point-size contact. The fast part of the signal starts when the holes are 1 cm far from the point-size electrode. Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 6

13 BEGe modeling and PSD features Pulse shape dependence of interaction position anode cathode exp data 0 mm 10 mm 15 mm 20 mm 25 mm 30 mm 35 mm charge [a.u.] time [10 ns] The hole are collected to the point-size contact along the same trajectories the final part of the charge signals is the same Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 7

14 BEGe modeling and PSD features Pulse shape dependence of interaction position anode cathode exp data 0 mm 10 mm 15 mm 20 mm 25 mm 30 mm 35 mm 40 current [a.u.] time [10 ns] The hole are collected to the point-size contact along the same trajectories the final part of the charge signals is the same Q(t) = qφ w(r(t)) I(t) = dq(t) dt = q dφw(r(t)) dt I max q Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 7

15 BEGe modeling and PSD features PSD: A/E parameter Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 8

16 BEGe modeling and PSD features PSD: A/E parameter A SSE q tot E SSE q tot (A/E) SSE = k, constant Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 8

17 BEGe modeling and PSD features PSD: A/E parameter A SSE q tot E SSE q tot (A/E) SSE = k, constant A MSE q SSEmax E MSE q tot (A/E) MSE < (A/E) SSE = k Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 8

18 PSD performances for external and internal background PSD applied to simulated data Validate the simulated PSD estimations by comparison with experimental data: discrimination results for 228 Th and 60 Co measurements Estimation of the rejection performances for internal sources of background: acceptance results for Q ββ discrimination results for 68 Ge and 60 Co measurements Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 9

19 PSD performances for external and internal background PSD applied to simulated and experimental data: 228 Th counts energy [kev] experimental 228 Th: DEP 90% SEP 7% FEP 11% Q ββ 52% simulated 208 Tl ( 228 Th daughter): counts DEP 90% SEP 6% FEP 9% (Q ββ 43%) energy [kev] shielding not included in the simulation Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 10

20 PSD performances for external and internal background PSD applied to simulated and experimental data: 60 Co counts experimental 60 Co: Q ββ 1.2% energy [kev] 1e counts simulated 60 Co: Q ββ 1.0% energy [kev] Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 11

21 PSD performances for external and internal background PSD of internal background counts energy [kev] simulated 0νββ: Q ββ 85% counts energy [kev] 1e simulated 60 Co: Q ββ 1.1% counts simulated 68 Ge: Q ββ 5% energy [kev] Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 12

22 Conclusion Conclusion Results and future works: A complete simulation of the signal formation and development has been developed and used to investigate the the Pulse Shape Discrimination features of BEGe detectors for the first time the BEGe PSD rejection performances for internal sources of background were studied and the acceptance is 1% for 60 Co and 5% for 68 Ge. keep on studying the impact of the detector parameters on pulse shape discrimination performances and the robustness of A/E method use the simulation to improve the PSD efficiency Simulation and modeling of BEGe detectors for GERDA Phase II Matteo Agostini (MPIK) 13

arxiv: v2 [physics.ins-det] 17 Jan 2011

arxiv: v2 [physics.ins-det] 17 Jan 2011 Preprint typeset in JINST style - HYPER VERSION Characterization of a broad energy germanium detector and application to neutrinoless double beta decay search in 76 Ge arxiv:12.5200v2 [physics.ins-det]