DOUBLE BETA DECAY OF 106 Cd - EXPERIMENT TGV (Telescope Germanium Vertical) EXPERIMENT SPT (Silicon Pixel Telescope)

Transcription

1 DOUBLE BETA DECAY OF 106 Cd - EXPERIMENT TGV (Telescope Germanium Vertical) EXPERIMENT SPT (Silicon Pixel Telescope) I. Štekl (IEAP CTU in Prague) on behalf of TGV collaboration CSNSM Orsay, France CU Bratislava, Slovakia IEAP, CTU Prague, Czech Republic JINR Dubna, Russia RRC - Kurchatov Institute Moscow, Russia

2 DOUBLE BETA DECAY OF 106 Cd EC/EC 2e b- + (A,Z) (A,Z-2) + (2 e ) + ( ) Experimental signature 2KXPd (+ for exc.s.) β+/ec e b- + (A,Z) (A,Z-2) + e + + (2 e ) + ( ) Experimental signature KXPd (+ for exc.s.) (β+β+) (A,Z) (A,Z-2) + e + + e + + (2 e ) + ( ) Experimental signature (+ for exc.s.)

3 Ag /EC EC/EC 106 Cd 1.25% Q(EC/EC) = 2770 kev (+ for e.s.) +/EC KXPd (+ for e.s.) νEC/EC 2KX Pd (~21 kev) (+ for e.s.) Main background: Cd KX-rays (~23 kev) Pd 0νEC/EC KXPd + LXPd ( ) 0νEC/EC 2KXPd + ( )

4 Experiment TGV-2 Laboratoire Souterrain de Modane, France Phase I ~ 10g (12 samples) of 106 Cd (75%) and ~ 3.2 g (4 samples) of Cd-nat. T= 8687h (Feb.2005 Feb.2006) Phase II ~ 13.6 g (16 samples) of 106 Cd (75%) T ~ 12900h (Dec.2007 July 2009) Background I no samples (Aug.2009 March 2010) Background II 16 samples of Cd.-nat (April )

5 Telescope Germanium Vertical (TGV-2) 32 HPGe planar detectors 60 mm x 6 mm with sensitive volume: 20.4 cm 2 x 6 mm Total sensitive volume: ~400 cm 3 Total mass of detectors: ~3 kg Total area of samples : 330 cm 2 Total mass of sample(s) : g Total efficiency : % E-resolution : Co LE-threshold : kev (5 6 kev) Double beta emitters: 16 samples (~ 50 µm ) of 106 Cd (enrich.75%) 13.6 g ~ 5.79 x atoms of 106 Cd HPGe Cd HPGe

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

7 PASSIVE SHIELDING Copper > 20 cm Airtight box Lead > 10 cm Polyethylene filled with boron 16 cm

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9 acquisition with 10g of 106 Cd after 8687 hours: additional analysis (2D, different energy windows) Phase I final result 2 EC / EC T1 / 2 ( Cd) y (90%)

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

11 106 Cd, T=12900h Cd-nat. T=3500h KXPd KXCd KXPd KXCd ROI ROI

12 Phase I Phase II EC/EC T 1/2 (90%CL) T 1/2 (90%CL) ( ,g.s.) 3.0 x yr 4.2 x yr ( ,512) 4.2 x yr 1.2 x yr ( ,1334) 3.1 x yr 1.0 x yr 0 res.( ,2741) x yr 0 res.(0 +?,2716) x yr β + /EC ( ,g.s.) 5.9 x yr 1.1 x yr ( ,512) 5.9 x yr 1.1 x yr ( ,1334) x yr β + β + ( ,g.s.) 6.0 x yr 1.4 x yr ( ,512) 5.7 x yr 1.7 x yr 2 β + β + ( ,g.s.) x yr (N.I.Rukhadze et al., Nucl.Phys. A 852 (2011) )

13 PROBABILITY K(%) PROBABILITY/0.95 EVENTS 100 KXPd 3_18 DET _18 DET ENERGY,KEV The calculated probability of detection of the peak of KX(Pd) 2 EC / EC EVENTS Likelihood probability function of 21 kev events T ( Cd) y (77% C. L.) 1/ 2 2 EC / EC 106 T ( Cd) y (90% C. L.) 1/

14 23 g of 106 Cd with enrichment of 98.4 % Plans on near future Planned measurements with 106 Cd: 1. TGV-2 (Ge detectors) (~15 g) cm 3 HPGe detector (~8 g) (modes with ) 3. SPT (Pixel detectors) (~8 g)

15 Approaches to double beta studies GERDA Detector = source SuperNEMO Tracking + scintillator CUORE Low-temp. detector COBRA Semiconductor + segmentation TGV II Setup based on semiconductor detectors COBRA extension Segmented CdTe pixel detectors (enriched Cd) Signature = two tracks of electrons from one pixel, Bragg curve Particle identification / rejection (alpha, electrons, photons) Pixel R&D projects Observable: 2 21keV X-rays from 106 Pd daughter originated in the enriched Cd foil TGV III (EC/EC) 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) K 1 K 2 K 1 Double-side event Single-side events K 1 K 2 K 1 K 2

16 Medipix clones 1. Medipix1 (64x64, 170x170mm 2 ) 2. Medipix2 (256x256, 55x55mm 2 ) TimePix (spectroscopic capabilities) 3. Medipix3 (in production, new features) TimePix2 USB readout, up to now only small area, not tuned for low background measurements Medipix2 Pixels: 256 x 256 Pixel size: 55 x 55 mm 2 Area: 1.5 x 1.5 cm 2 Medipix2 Hexa Pixels: 512 x 768 Pixel size: 55 x 55 mm 2 Area: 3 x 4.5 cm 2

17 Response examples Particle type identification Clusters selected according to size, roundness, linearity,... Alphas Electrons Muons Muons + electrons a 214 Bi 214 Po 210 Pb May 5, 2010 Pavel Cermak

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

19 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 s time window, Pb shield 3) Development of coincidence mode: stack of pixel detectors (face2face arrangement).

20 Counts / hour Intrinsic background Measured by low-background setup in Modane lab HPGe planar detector, 150cm 3, range 20keV 1.5MeV Chipboard with Si detector E, kev Contributions per unit (comparison of samples and Si module) [mbq/unit]: Bonding (In+Sn) Readout chip Empty PCB Si module 228 Th < 10-8 < ± ± Th < 10-6 < ± ± K < 10-7 < 6.2 < ± 28

21 Intrinsic background (PCB material screening results) material Mass (g) Time (s) Unit 226 Ra 210 Pb 228 Ra 228 Th 40 K FR4 (original PCB) mbq/kg 14259± ± ± ± 648 <2025 (Kapton + Ad+Cu) mbq/kg 207±76 <3200 < ±76 <1760 Cu foil mbq/kg <126 <4500 <293 < ± 315 Adhesive mbq/kg <556 <16000 <1400 <1400 <9000 Coverlay (mask) mbq/kg <1500 <40000 <3500 <3500 <28000 Cuflon mbq/kg <16 <134 <39 <16 <280

22 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) E1.vs.E2 SSE Entries 15 ROI Energy spectrum (up to 300keV)

23 Pixel detector stack and coincidence unit development First prototype of rotated stack ready Two Si chips available. Tuning and testing USB 2 readout already in use for 8 Si Pixel det. measurement (time window 1s) Stack inside Al Box Down carrier board Up carrier board Rotated stack PCBs Mother board

24 SPT setup proposal Estimation of limit for EC/EC decay of 106 Cd for 1 pair of Timepix quads: If background = 0 : T 1/2 > (e. t. N at. ln2) / ln (1-CL) = 1, years 90% CL ln (1-CL) = 2.3 e... full efficiency (for SPT = 8,54 %) t... time of measurement [years], expected 4 years N at... number of 106 Cd atoms in foil, 98% of enrichment N at = atoms To reach limit of years: We would need 5-7 quad Timepix pairs in 1. prototype (for 8 gr. we need quad pairs)

25 Summary and future plans Study of 2 EC/EC of 106 Cd, modes with gammas (HPGe detector) TGV-2 setup (based on HPGe detector telescope) has provided result comparable with theoretical predictions 23 grams of 106 Cd (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) 1) Background measurement with single Si pixel detector made of cuflon PCB: in LSM, 2-3 months; 1s time window, Pb shield 2) Background measurement with prototype of Si pixel stack (coincidence mode, double side events) 3) Si pixel stack made of cuflon PCB + background measurement 4) Construction of quad pixel detector stack one pair, (up to 5-7 pairs).

26 Backup slides

27 0 EC/EC DECAY 2e b- + (A,Z) (A,Z-2) + 2X + ( brem, 2, e + e -, e- int ) E,.. = M - e1 - e2 Suppression factor is ~ 10 4 (in comparison with EC +(0 )) M. Doi and T. Kotani, Prog. Theor. Phys. 89 (1993) EC/EC Resonance Conditions Q (E*) = M - E* - 2E b Q res < 1 kev Enhancement factor can be on the level ~ 10 6! (for 112 Sn) - J. Bernabeu et.al., Nucl. Phys. B 223 (1983) 15 0 EC/EC Resonant Decay of 106 Cd M= 2770±7.2 kev E*= kev E K =24.3 kev E L =3.33 kev E*= kev E K =24.3 kev E K =24.3 kev

28 J.Shitov Phase II data processing

29 KK-pair E 2 E 1 E 2 E 2 E 1 E 1 =E 2 = K Pd D -single E 1 E 1 = D D -paired KK TGV signal patterns β + β + E 1 (KK+ D )-pair E 1 E 2 E E 1 +E 2!= 511 kev E 1 <511 kev E fired E 1 =511 kev E single E 1 +E 2 =511 kev E 2 E 1 E 2 -pair candidate E 2 E 2 E 1 E 1 E 1 E 2 E 1 E 1 +E 2 = D (KK)-pair + D -satellite (single or paired) E 1 E 2 E paired -pair + -satellite (single, paired, or fired)

30 Comparision of background in Phase I and Phase II

31 241 Am new foils old foils

32 Energy spectra in the 1st channel Single Double Double + KX

33 Energy spectra in the 2nd channel Single Double Double + KX

34 Counts / hour Intrinsic background in Timepix Counts / hour Measured by low-background setup in Modane lab HPGe planar detector Mafalda, 150cm 3, range 20keV 1.5MeV E, kev E, kev Chipboard with Si detector Chipboard with CdTe detector ev. / hour ev. / hour Th-228: (165 ± 10) mbq K-40: (117 ± 28) mbq Th-228: (156 ± 10) mbq K-40: (122 ± 14) mbq Co-60: (60 ± 21) mbq Ta-182: (2065 ± 82) mbq Ag-110m: (483 ± 15) mbq

35 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)