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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. 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.) 622 +/EC KXPd + 2511(+ for e.s.) 1046 2+ 511.9 2νEC/EC 2KX Pd (~21 keV)(+ for e.s.) Main background: Cd KX-rays (~23 keV) 511.9 0νEC/EC KXPd + LXPd +2741(2229 + 512) 0+ 0νEC/EC 2KXPd +(1160 + 1046+ 512) 106Pd

  3. Laboratoire Souterrain de Modane, France Phase I ~ 10g (12 foils) of 106Cd (75%) and ~ 3.2 g (4 foils) of Cd-nat., T= 8687h (Feb.2005 – Feb.2006) Phase II ~13.6 g (16 foils) of 106Cd (75%), T ~ 12900h (Dec.2007 – July 2009) Background I no samples(Aug.2009 – March 2010) Background II 16 samples of Cd.-nat (April 2010 – …2011)

  4. Telescope Germanium Vertical (TGV-2) 32HPGe 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 : 4050 keV (5  6 keV) Double beta emitters: 16 samples (~ 50 µm ) of 106Cd (enrich.75%) 13.6 g ~ 5.79 x 1022 atoms of 106Cd HPGe Cd HPGe

  5. TGV-2 Detectors: 32 HPGe Ø 60 mm x 6 mm Sensitive volume 20.4 cm2 x 6 mm Total sensitive volume~ 400 cm3 Total mass ~3 kg Details of cryostat ~2500 g (Al, Cu, …) Al ~ 1200 g (including holders ~ 360 g) Cu ~ 1300 g

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

  7. Phase I final result • acquisition with 10g of106Cd after 8687 hours: additional analysis (2D, different energy windows)

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

  9. Phase I Phase II 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 yr 1.0 x 1020 yr 0res.(0+→4+,2741) - 1.7 x 1020 yr 0res.(0+→ ?,2716) - 1.6 x 1020 yr β+/EC (0+→0+,g.s.) 5.9 x 1019 yr 1.1 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 yr 1.4 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 (N.I.Rukhadze et al., Nucl.Phys. A 852, 2011, 197-206)

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

  11. Plans on near future 24 g of 106Cd with enrichment of 98.4 % • Planned measurements with 106Cd: • TGV-2 (Ge detectors) (~14-15 g) • 600 cm3 HPGe detector (~24 g) (modes with g) • SPT (Pixel detectors) (~8-10 g)

  12. Approaches to double beta studies K1 K1 K2 TGV II GERDA SuperNEMO CUORE COBRA Setup based on semiconductor detectors Semiconductor + segmentation Detector = source Tracking + scintillator Low-temp. detector Pixel R&D projects COBRA extension TGV III (EC/EC) • Segmented CdTe pixel detectors (enriched Cd) • Signature = two tracks of electrons from one pixel, Bragg curve • Particle identification / rejection (alpha, electrons, photons) • Si pixel detectors in coincidence mode • Thin foil of enriched isotope • Signature = two hitted pixels with X-rays of precise energy • Efficiency (factor 2x comparing with TGV II) • Particle identification (alpha, electrons) K1 K1 K2 K2 Observable:2× 21keV X-rays from 106Pd daughter originated in the enriched Cd foil Double-side event Single-side events

  13. Timepix detector 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) Portable tracking detector Room temperature & noiseless operation

  14. 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

  15. 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

  16. Activities performed with Si pixel detectors 1) Selection of materials, design of detector : to suppress intrinsic background 2) Background measurement with single Si pixel det.: surface + underground (LSM), 1 month; 1s + 0.1 s time window, Pb shield 3) Development of coincidence mode:stack of pixel detectors (face2face arrangement).

  17. 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]:

  18. Intrinsic background (PCB material screening results)

  19. Measurement of background Background measurements with Si pixel detectors in LSMand IEAP CTU (1s or 0.1s time window) were finished.

  20. 1 s frame Energy Spectrum(SSE = two X-rays registered in one frame by different pixels) Prague Modane

  21. 1s frame Energy Spectrum(SSE, distance between pixels 0.7mm - 4mm) Prague Modane

  22. E1 vs E2 (SSE, 0.7mm - 4mm) Prague Modane

  23. Data given for 487 hours

  24. Timepix stack and other developments First prototype ready and tested (face to face configuration) Chip support (CuFlon or Pure copper) Flexible PCB Detectors face to face Support system Detectors very near to each other Current Timepix stack Planned next version • Timepix Stack Prototype tested with D class Timepix • CuFlon Based PCB ready for wire bonding • Considering Flexible PCB for next generation of stack • Flexible PCB based design allows to keep the detector very close to each other First prototype of CuFlon based chip board

  25. 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 5-7 quad Timepix pairs in 1. prototype (for 8 gr. we need 25-30 quad pairs)

  26. Summaryandfutureplans • Study of 2nEC/EC of 106Cd, modes with gammas (HPGe detector) • TGV-2 setup (based on HPGe detector telescope TGV) has provided result comparable with theoretical predictions • 24 grams of 106Cd (98.4% enrichment) available – TGV, SPT, background level • Considering next generation setup SPT (Silicon Pixel Telescope) based on Si pixel detectors TimePix • Heading for a prototype based on the four-fold Si Timepix stack (face-to-face arrangement) The study of the posibility to measure 0nEC/EC decay (152Gd g.s., 112Snexc. state– resonance enhancement of the 0nEC/EC process if Q – Qr < 1 keV) Z.Sujkowski, S.Wycech, Phys. Rev. C70, 052501, 2004 J.Bernabeu, A. deRujula, C.Jarlskog, Nucl. Phys. B223, 15 (1983) signature – X-rays < 100 keV + g or e-e+ or Majoron advantage: good value of the rates between 0nEC/EC and 2nEC/EC processes

  27. Backup slides

  28. 0EC/ECDECAY 2eb- + (A,Z) → (A,Z-2) + 2X + (brem, 2, e+e-, e-int) E,.. = M - e1 -e2 Suppression factor is ~ 104 (in comparison with EC+(0)) – M. Doi and T. Kotani, Prog. Theor. Phys. 89 (1993)139. 0EC/ECResonance Conditions Q‘(E*) = M - E* -2Eb Q’res < 1 keV Enhancement factor can be on the level ~ 106! (for 112Sn) - J. Bernabeu et.al., Nucl. Phys. B 223 (1983) 15 0EC/ECResonant Decay of 106Cd M=2770±7.2 keV E*=2741.0 keV EK=24.3 keV EL=3.33 keV E*= 2717.6keV EK=24.3 keV EK=24.3 keV

  29. KXPd The calculated probability of detection of the peak of KX(Pd) Likelihood probability function of 21 keV events

  30. KKTGV signal patterns β+β+ KK-pair E1<511 keV E2 E1 E2 E2 g511-fired E1 E1 E1 gD-single E1=511 keV E2 E2 E1 E1 g g511-single E1=gD E1 E1 gD-paired E1+E2=511 keV bb-pair candidate (KK)-pair + gD-satellite (single or paired) E2 E2 E1 E1 g g E2 E2 E1 E1 g511-paired E1+E2 = gD g g 1. E1+E2 != 511 keV 2. E2 g E1 E1=E2 = KPd (KK+gD)-pair g E2 E1 g bb-pair + g-satellite (single, paired, or fired)

  31. Comparision of background in Phase I and Phase II

  32. 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 %

  33. E1.vs.E2 SSE Entries 15 Background signal measurement 20 days of experimental data from LSM, shielded 5cm of Pb, 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)

  34. 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)

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