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BACKGROUND REJECTION AND SENSITIVITY FOR NEW GENERATION Ge DETECTORS EXPERIMENTS.

BACKGROUND REJECTION AND SENSITIVITY FOR NEW GENERATION Ge DETECTORS EXPERIMENTS. Héctor Gómez Maluenda University of Zaragoza (SPAIN) hgomez@unizar.es. IDM’10 Montpellier, July 2010. OUTLINE. Motivation. Setup. Geometry & Materials. Simulated Events. Pulse Generation.

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BACKGROUND REJECTION AND SENSITIVITY FOR NEW GENERATION Ge DETECTORS EXPERIMENTS.

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  1. BACKGROUND REJECTION AND SENSITIVITY FOR NEW GENERATION Ge DETECTORS EXPERIMENTS. Héctor Gómez Maluenda University of Zaragoza (SPAIN) hgomez@unizar.es IDM’10 Montpellier, July 2010.

  2. OUTLINE • Motivation. • Setup. • Geometry & Materials. • Simulated Events. • Pulse Generation. • Pulse Analysis. • Results • Summary & Conclusions. IDM’10 Montpellier, July 2010.

  3. MOTIVATION • Germanium detectors have been used in several experiments searching for Rare Events: • Detection Efficiency. • Energy Resolution. • Robustness. • … • Some new experiments are based on the operation of new generation Ge detectors: • Dark Matter  Edelweiss, CDMS. • Double Beta Decay  Gerda, Majorana. • Expected sensitivity of these experiments needs to develop different techniques for background events suppression keeping high detection efficiency levels. • Analysis of the Pulse Shape generated in segmented detectors with 3D resolution, seems to be one of the most powerful tools to identify background events, for further rejection (H. Gómez et al. Astrop. Phys. 28 (2007) 435-447). IDM’10 Montpellier, July 2010.

  4. SETUP • The goal of this work is try to estimate the background rejection capability of 3D-PSA in a 0 experiment using segmented Ge detectors. Q ~ 2039 keV (76Ge). For a <m>~50 meV sensitivity: ε~75-80 % b ~10-3 c keV-1 kg-1y-1 • Simulation of background and signal events. • Pulse generation from these events. • Pulse Shape Analysis (PSA). IDM’10 Montpellier, July 2010.

  5. GEOMETRY & MATERIALS • Geometry has been defined versatile thinking on the possibility of further changes: • Detector: • Natural Germanium cylinder (D=h). • Mass between 0.1 and 4 kg. • Copper Cryostat: • 3 parts (based on IGEX design). • Dimensions dependent on detector size. • Experimental Place: • 2 m diameter sphere. • Big enough to increase the setup. • Air inside the sphere. IDM’10 Montpellier, July 2010.

  6. SIMULATED EVENTS • Apart from signal events, main background contributions in the 2.0-2.1 MeV Region of Interest have been considered: • Signal: 0 events (DECAY 0). • Background: Internal 60Co and 68Ge (GEANT4). 60Co in Cu cryostat (GEANT 4). External 208Tl and 214Bi (GEANT4). 2 events (DECAY 0). 214Bi 208Tl 60Co 0 60Co-68Ge 2 IDM’10 Montpellier, July 2010.

  7. SIMULATED EVENTS • The background considered represents ~95% of the total background in the RoI. • Several tests have been carried out to validate the generated events. 2 0 Internal 60Co External 214Bi IDM’10 Montpellier, July 2010.

  8. PULSE GENERATION • To have 3D spatial resolution is necessary to study the net signal an the induced ones. True Segment IDM’10 Montpellier, July 2010.

  9. PULSE GENERATION • The pulse is the representation of the charge variation vs time: • Voltage V0 is applied to the outer electrodes of the detector. IDM’10 Montpellier, July 2010.

  10. Finiteelement calculation PULSE GENERATION • The pulse is the representation of the charge variation vs time: • Voltage V0 is applied to the outer electrodes of the detector. • Finite element calculation to obtain E. IDM’10 Montpellier, July 2010.

  11. PULSE GENERATION • The pulse is the representation of the charge variation vs time: • Voltage V0 is applied to the outer electrodes of the detector. • Finite element calculation to obtain E. • Ew (weighting field) is the theoretical existing field when all the electrodes are with V=0 excepting one. IDM’10 Montpellier, July 2010.

  12. Time (ns) PULSE GENERATION • Net Signal: • 2 singular points in the pulse per energy deposit. • Total area proportional to the energy. • Only radial sensitivity. IDM’10 Montpellier, July 2010.

  13. PULSE GENERATION • Induced Signal: • No new temporal information. • Null net area. • Absolute area (AA) as representative value. • Signal amplitude and AA lower than net signal. IDM’10 Montpellier, July 2010.

  14. PULSE ANALYSIS • Net Signal: • A singular point corresponds to a maximum in the pulse derivative. • Analysis is based on maxima identification. 2 maxima  Mono Site Event 3 or more  Multi Site Event IDM’10 Montpellier, July 2010.

  15. PULSE ANALYSIS • Net Signal:Characteristic Time • Electronics could distort pulses decreasing the maxima identification capability. • This effect has been taking into account by convoluting pulses with a transfer function. RC=20 ns RC=40 ns RC=20 ns RC=40 ns IDM’10 Montpellier, July 2010.

  16. PULSE ANALYSIS • Induced Signal: • Net signal provides information about energy and r coordinate of the event. • z andφ coordinates could be defined form induced signals. • For multisite events these coordinates are for Center of Energy point (CoE). IDM’10 Montpellier, July 2010.

  17. PULSE ANALYSIS • Induced Signal: • Absolute Area (AA) is the most representative feature of induced signals • AA value is independent of Characteristic Time. • Analysis is based on AA comparison with the corresponding CoE event. MONOSITE MULTISITE Pz & Pφ ≤ 1  Monosite Pz or Pφ > 1  Multisite IDM’10 Montpellier, July 2010.

  18. RESULTS • Pulse generation and analysis has been carried out in 2 and 4 kg Ge crystals. • First step: Net Signal Analysis (after anticoincidence between segments). 40 ns seems to be the best value for RC 2 kg 4 kg RC (ns) IDM’10 Montpellier, July 2010.

  19. RESULTS • Second Step: Induced signals analysis (only for non rejected events). 2 kg; RC = 40 ns 4 kg; RC = 40 ns /(b)1/2 after induced signal analysis IDM’10 Montpellier, July 2010.

  20. RESULTS *Values from H. Gómez et al, Astroparticle Physics 28 (2007) 435-447 IDM’10 Montpellier, July 2010.

  21. RESULTS *Values from H. Gómez et al, Astroparticle Physics 28 (2007) 435-447 IDM’10 Montpellier, July 2010.

  22. RESULTS • Estimation of the sensitivity from the ε and b values obtained 2 kg 4 kg IDM’10 Montpellier, July 2010.

  23. RESULTS • Estimation of the sensitivity from the ε and b values obtained IDM’10 Montpellier, July 2010.

  24. SUMMARY & CONCLUSIONS • Germanium detectors are one of the best options for experiments searching for Rare Events. • 3D PSA in segmented detectors seems to be one of the most powerful background rejection techniques. • A setup for pulse generation and analysis from simulated events has been developed to study this technique in 76Ge 0 experiment. • Obtained results show that <m> ~ 50meV could be reachable with this technique. • It is necessary to make new studies focused on Dark Matter. IDM’10 Montpellier, July 2010.

  25. BACKGROUND REJECTION AND SENSITIVITY FOR NEW GENERATION Ge DETECTORS EXPERIMENTS. Héctor Gómez Maluenda University of Zaragoza (SPAIN) hgomez@unizar.es IDM’10 Montpellier, July 2010.

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