pulse shape analysis with segmented germanium detector
DESCRIPTION
Pulse Shape Analysis with Segmented Germanium Detector. Xiang Liu, Max-Planck-Institut f ü r Physik. Motivation Pulse properties Analysis procedure Some results Outlook. Physics of Massive Neutrinos, Blaubeuren, July 1-5, 2007. Motivation: Single-site vs. Multi-site. Range log(R [mm]). - PowerPoint PPT PresentationTRANSCRIPT
Pulse Shape Analysiswith Segmented Germanium Detector
Xiang Liu, Max-Planck-Institut für Physik
1. Motivation2. Pulse properties3. Analysis procedure4. Some results5. Outlook
Physics of Massive Neutrinos, Blaubeuren, July 1-5, 2007
Motivation: Single-site vs. Multi-site
Blaubeuren, July 1-5, 2007 Page 2
Photon: Compton scattering multiple energy deposits
02: energy deposit locally, within 1mm.
208Tl
2614keV photon(Geant4 simulation)
02: 2 electrons
Range log(R [mm])
NIM A 570 (2007) 479-486
SSE MSE
Motivation: 3-D segmentation along z, & r
Blaubeuren, July 1-5, 2007 Page 3
GERDA Phase-II prototype detector: 18 segments (3 fold along z, 6 along ) No segment along r, technical difficultySolution Pulse Shape Analysis (PSA)
Electrons & holes drift along the applied field at ~1cm/100ns, inducing charge in electrodes. Rise part of pulse contains information about energy deposit locations.
Pulse shape properties
Blaubeuren, July 1-5, 2007 Page 4
Single site event (SSE):
Multiple site event (MSE):
MSE tends to have more complicated pulse structures.
Knee indicates that one charge carrier reaches electrode and stops drifting
Pulse shape analysis procedure
Blaubeuren, July 1-5, 2007 Page 5
SSE candidate
MSE candidate
PSA procedure:1. Collect SSE and MSE samples,
independent of pulse shapes.2. Study the PS difference,
train PSA package.3. Apply the trained PSA package to
identify signal and background.
Test stand with 18-fold Ge detector
Collecting SSE sample:
Blaubeuren, July 1-5, 2007 Page 6
Double escape events (DEP): one electron and one positron with sum energy 1592keV
Single Compton scattering events: single electron with energy 2039keV
2614keV
Pulse shape analysis packages
Blaubeuren, July 1-5, 2007 Page 7
Likelihood method: pulse rise time current FWHM
Neural Network method: sampled pulses as input
Define discriminator
Neural Network PSA results
Blaubeuren, July 1-5, 2007 Page 8
Samples DEP 1620keV 2614keV
Fraction identified by NN as signal 89% 54% 44%
MC simulation: Fraction with R90<2mm 89% 55% 30%
Single segment events
DEP1592keV
Bi-212 1620keV
Outlook1: Pulse shape simulation
Blaubeuren, July 1-5, 2007 Page 9
Need simulation to understand: energy deposit range pulse shape
Understand second order effect: charge carrier drifting velocity depends on crystal axis, impurity concentration & non-uniformity, trapping, preamplifier bandwidth, …
Close collaboration with Majorana MC group
NIM doi:10.1016/j.nima.2007.03.035[Nucl-ex/0701004]
Outlook2: New test stand under construction
Blaubeuren, July 1-5, 2007 Page 10
Both Ge detector and source in Vacuum: photon UV laser
3-D scan of the detector.
Outlook3: application example: Mirror charge
Blaubeuren, July 1-5, 2007 Page 11
Mirror charge from neighboring segments gives additional information along z & .
enhance MSE identification
identify signal at segment boundaries
identify surface contamination ()
phiz
Mirror charge amplified by factor of 4
Conclusion
Blaubeuren, July 1-5, 2007 Page 12
Measurement with 18-fold Ge detector proves the technique and its ability for background identification. NIM doi:10.1016/j.nima.2007.03.035 [nucl-ex/0701004], nucl-ex/0701005
First analysis proves that properly-trained pulse shape analysis package identifies most multi-site background events. arXiv:0704.3016
A new test stand is under construction at MPI Munich, where segmented Ge detector will be studied in detail with , , e sources and UV laser.
With detailed simulation and mirror charge, PSA is expected to further identify photon and surface backgrounds improve signal efficiency
Backup2: NN PSA results with DEP, continued
Blaubeuren, July 1-5, 2007 Page 13
Fraction of SSE (MSE) as correctly identified by NN as SSE (MSE):
Backup1: NN PSA results with DEP
Blaubeuren, July 1-5, 2007 Page 14
Fraction of SSE:
Fraction identified by NN as SSE:
Backup2: Pulse shape analysis packages
Blaubeuren, July 1-5, 2007 Page 15
Backup3: Mirror charge
Blaubeuren, July 1-5, 2007 Page 16
Mirror charge asymmetry of neighbor segments:
NIM doi:10.1016/j.nima.2007.03.035 [Nucl-ex/0701004]