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Search for double electron capture in 106 Cd using HPGe detectors and Si pixel detectors

Search for double electron capture in 106 Cd using HPGe detectors and Si pixel detectors. TGV experiment – TGV II detector description, results of Phases I and II Present status - u tilization of Si pixel detectors ( MC simulations , r esults of background measurements ) Future plans.

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Search for double electron capture in 106 Cd using HPGe detectors and Si pixel detectors

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  1. Search for double electron capture in 106Cd using HPGe detectors and Si pixel detectors TGV experiment –TGV II detector description, results of Phases I and II Present status - utilization of Si pixel detectors (MC simulations, results of background measurements) Future plans Ivan Štekl for TGV collaboration Institute ofExperimentalandAppliedPhysics CzechTechnical University in Prague Since 2000, focus on 2nEC/EC decay of 106Cd • JINR Dubna, Russia • IEAP CTU in Prague, Czech Republic • CSNSM Orsay, France

  2. Decay modes + signatures 1+ 106Ag 0+ 4+ 2741.0 106Cd 2717.6 ++ +/EC EC/EC 1.25% 1160 2741 2229 1557.7 3+ Q(EC/EC) = 2770 keV  7.2 0+ 1133.8 ++ 4 511(+  for e.s.) 1046  622 +/EC KXPd + 2511 (+  for e.s.) 2+ 511.9 2νEC/EC 2KX Pd (~21 keV) (+  for e.s.) Main background: Cd KX-rays (~23 keV)  511.9 0+ 0νEC/ECKXPd + LXPd +2741(2229 + 512) 106Pd 0νEC/EC 2KXPd +(1160 + 1046+ 512)

  3. 32 HPGe planar detectors 60 mm x 6 mm with sensitive volume: 20.4 cm2 x 6 mm Total sensitive volume: ~400 cm3 Total mass of detectors: ~3 kg Total area of samples : 330 cm2 Total mass of sample(s) : 10  25 g Total efficiency : 50  70 % E-resolution :3  4 keV @ 60Co LE-threshold : 5  6 keV 16 samples (~ 50 µm ) of 106Cd (enrich.75%) 13.6 g ~ 5.79 x 1022 atoms of 106Cd HPGe Cd HPGe

  4. Detectors: 32 HPGe Ø 60 mm x 6 mm Sensitive volume 20.4 cm2 x 6 mm Weight of cryostat ~2500 g (Al, Cu, …) Al ~ 1200 g (including holders ~ 360 g) Cu ~ 1300 g

  5. PASSIVE SHIELDING (TGV islocated in LSM) Copper > 20 cm Airtight box Lead > 10 cm Polyethylene filled with boron 16 cm

  6. Schedule of TGV II experiment: (in Laboratoire Souterrain de Modane, France) Phase I ~ 10g (12 samples) of 106Cd (75%) T= 8687h (Feb.2005 – Feb.2006) Phase II ~ 13.6 g (16 samples) of 106Cd (75%) T ~ 12900h (Dec.2007 – July 2009) Background I no samples (Aug.2009 – Mar.2010) Background II 16 samples of Cd.-nat(Apr.2009 – …2010)

  7. Phase I final result • acquisition with 10g of106Cd after 8687 hours: additional analysis (2D, differentenergywindows) T1/2 = 1.0 · 1020y(Suhonen) T1/2 > 3.0 · 1020y(TGV-2) T1/2 = 8.7 · 1020y(Hirsch) T1/2 = 4.4 · 1021y(Simkovic)

  8. -line 238 keV -line 352 keV Counts / day /detector Counts / day /detector

  9. Comparision of background in Phase I and Phase II

  10. Phase II, 13.6g of 106Cd, T=12900h KXPd KXCd ROI ROI KXCd ROI KXPd ROI

  11. How it compares with calculations > 4.2 1020 p.w. closed approaching

  12. TGV-2limits on double beta decay of 106Cd Phase IPhase II (10g of106Cd,8687h) (13.6g of 106Cd,12900h) EC/ECT1/2 ≥ …(90%CL)T1/2 ≥ … (90%CL) (0+→0+,g.s.) 3.0 x 1020 yr 4.2 x 1020 yr (0+→2+1,512) 4.2 x 1019 yr 1.2 x 1020 yr (0+→0+1,1334) 3.1 x 1019 yr1.0 x 1020 yr 0res.(0+→4+,2741) - 1.7 x 1020 yr 0res.(0+→ 2718) - 1.6 x 1020 yr β+/EC (0+→0+,g.s.) 5.9 x 1019 yr1.1 x 1020 yr (0+→2+1,512) 5.9 x 1019 yr 1.1 x 1020 yr (0+→0+1,1334) - 1.6 x 1020 yr β+ β+ (0+→0+,g.s.) 6.0 x 1019 yr1.4 x 1020 yr (0+→2+1,512) 5.7 x 1019 yr 1.7 x 1020 yr 2β+ β+ (0+→0+,g.s.)- 1.3 x 1020 yr

  13. TGV-III (SPT) idea Si Si Cd foil Control unit The potential of the TGV II setup (based on HPGe detectors) canbeextendedusing more enrichedmaterial, biggerweightandlonger acquisition time Considering to build a new generation of the setup based on Si pixel detectors Timepix SPT - Silicon Pixel Telescope Advantages: better efficiency comparing with TGV II (factor 2) information about energy + position of registered X-ray particle recognition (background vs. signal) much less material needed (lower background) measurement at room temperature (easy access)

  14. Timepix detector • Portable tracking detector • Room temperature & noiseless operation Chipboard + USB readout interface Vacuum operation, no cooling USB readout interface (developed in IEAP CTU in Prague), frame-rate up to 5 fps (USB 1.1) Compact size, Plug&Play, hot swap Fully USB powered Integrated source of variable detector bias voltage (5 – 100V) Pixelman software package + plugin for particle identification Pixelman software package (developed in IEAP CTU in Prague)

  15. Response examples • Particle type identification • Clusters selected according to size, roundness, linearity,... Alphas Electrons Muons Muons + d electrons b a 214Bi  214Po  210Pb Pavel Cermak

  16. SPT MC simulations (1) K1 K2 a) Distance face to face in detector pair: 2 mm (detector - source = 1mm) b) Detector dimensions: 1.408 cm x 1.408 cm x 2 mm number of pixels: 256 x 256 (pixel size: 55 x 55 microns) detector material: Si backside contact thickness: 1800 angstroms backside contact material: Aluminum c) Source foil: 1.2 cm × 1.2 cm × 50 mm Vertex and physics: Two 21 keV gamma (106Pd X-rays) emitted from single point chosen in bulk of source in full isotropic solid angle Tagged patterns: Each X-ray is fully detected in the single pixel either: 1) single-side events (SSE) – pixels fired in the same detector 2) double-side events (DSE) – pixels fired in both detectors 3) Total number of good KK-events  SSE+DSE Single-side-events K1 K1 K2 K2 Double-side-event

  17. SPT MC simulations (2) SPT efficiency of registration (compare with 5.5% for TGV-II): Setup with 2 mm thick Si Timepix detector, source distance = 1mm: Number of good KK-events registered in two pixels: 12.71 % - double-side events (DSE): 44.11 % - single-side events (SSE): 55.89 % - single-side events in adjacent pixels: 0.009 % Number of events with energy deposit in foil: 76.0 % Setup with 2 mm thick Si Timepix detector, source distance = 1mm: Number of good KK-events registered in two pixels: 16.66 % - double-side events (DSE): 42.32 % - single-side events (SSE): 57.68 % - single-side events in adjacent pixels: 0.16 % Number of events with energy deposit in foil: 76.2 %

  18. Distance of pixels hit (comparison of MC and meas.) Results of MC: a) MC results: KK events, source-detector distance = 1mm D < 2 mm => 34.5% of registered KK events D (0.7 – 4) mm => 68% of registered KK events Mean distance = 3.2 mm KK events, source-detector distance = 0mm D < 2 mm => 84.7% of registered KK events D < 4 mm => 98.7% of registered KK events Mean distance = 1.2 mm b) For background measurement: D (0.7 – 4) mm => 25% of registered bg events Using distance cut D (0.7-4) mm Bg measurement from LSM: Improving S/B ratio by factor of 2.6

  19. Intrinsic background Measured by low-background setup in Modane lab HPGe planar detector, 150cm3, range 20keV – 1.5MeV Chipboard with Si detector Contributions per unit (comparison of samples and Si module) [mBq/unit]:

  20. E1.vs.E2 SSE Entries 15 Background signal measurement 20 days of experimental data from LSM, shielded 5cm of Pb, recording 1s frames Looking for SSE candidates (2 clusters in the frame) Only random coincidences, 0 events in the ROI (19-23 keV) ROI Energy spectrum (up to 300keV)

  21. SPT setup proposal Estimation of limit for EC/EC decay of 106Cd for 1 pair of Timepix quads: If background = 0 : T1/2 > (e . t . Nat . ln2) / ln (1-CL) = 1,95 × 1020 years 90% CL ln (1-CL) = 2.3 e ...... full efficiency (for SPT = 8,54 %) t ...... time of measurement [years], expected 4 years Nat ... number of 106Cd atoms in foil, 98% of enrichment  Nat = 1.89 × 1021 atoms To reach limit of 1021 years: We would need 5 quad Timepix pairs

  22. Next step – using stack of Timepix detectors • To build a prototype based on the four-fold Timepix stack Developed slightly modified boards allowing face-to-face configuration Further optimization of the chip carrier board (material of PCB, minimizing amount of material close to the chip)

  23. Summaryandfutureplans • Study of 2nEC/EC of 106Cd • TGV-2 setup (based on HPGe detector telescope) has provided result comparable with theoretical predictions – plan new start with more enriched foils (98.4% of 106Cd) • Developing next generation setup SPT (Silicon Pixel Telescope) based on Si pixel detectors TimePix – measurement and tuning of intrinsic background, a prototype based on the four-fold Timepix stack. Not tuned for low-bg applications, working on detection module design optimization, material selection (teflon PCB, capton). Studying background signals – Si TimePix detector located in Modane underground lab, 3 months of data (3 weeks processed). Dreaming of 5 quad pairs setup running for couple of years to reach region of 1021 years.

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