Download - Results of Phase I of the TGV II Experiment

Results of Phase I of the TGV II Experiment

• History (TGV I)History (TGV I)• TGV IITGV II• Data processingData processing• Phase I resultsPhase I results• Phase II preparationPhase II preparation

Pavel Cermak

Pavel Cermak 2June 13, 2006

History (TGV I)

yT 193.33.1

22/1 10)2.4(

)%90(105.1 2102/1 CLyT

afterafter 8700 ho 8700 hoursurs::

sshieldinghielding: 20cm : 20cm of of eleelecctrolytictrolytic copper copper, , airtightairtight box, BPE box, BPE

open cryostat

cryostat, PAs

(1994 – 2000)(1994 – 2000) designed to study double beta decay ofdesigned to study double beta decay of 48Ca tetelescope composed oflescope composed of 16 HPGe 16 HPGe planar planar detdetectorsectors samples: foils of enriched samples: foils of enriched 48Ca (80%),,

total mass 1.08gtotal mass 1.08g


History (TGV I)History (TGV I) TGV IITGV II Data processingData processing Phase I resultsPhase I results Phase II preparationPhase II preparation


TGV II

),(22 10646

10648 raysXPdCde e

(2000 – ...)(2000 – ...) to investigate to investigate processes in processes in 106106Cd (to Cd (to

focus on 2focus on 2EC/EC channel)EC/EC channel)

observables: observables: 2 characteristic X-rays 2 characteristic X-rays from de-excitation of from de-excitation of 106106PdPd shell shell

keVEkeVkeV XECEC 2319:ROI,2778Q /

2EC/EC:


TGV II (predictions, measurements)

T1/2 = 1.0·1020 y (Suhonen)

8.7·1020 y (Hirsch)

4.4·1021 y (Simkovic)

Theoretical predictions:

Experimental results: (mostly to excited states of 106Pd)

T1/2 (g.s → g.s. ) > 5.8·1017 y

T1/2 > 6.2·1018 y (Barabash, HPGe detector + Cd foil,

Modane)T1/2 > 7.3·1019 y (Belli, NaI(Tl), geometry similar to TGV, Gran Sasso)

(Georgadze, measurement with 116CdWO4 scintilators, Solotvina)


TGV IILocation: Modane Underground Laboratory (4800 m.w.e.)

SM

Signal w ires

PA

Cold finger

Pb

Cu

LN Dewar

LN2

N2

Borated Polyethylene

1 m

TG V -2

Copper> 20 cm

Airtight box

Lead >10cm

Boron filled polyethylene

16cm


TGV II (cryostat)

32 HPGe planar detectors ø60 mm x 6 mm (active area 2040mm2)

Total mass of samples: 10 - 25 g E-threshold: ≈ 10 keV Samples: 12x 106Cd foils (~10g)

HPGe

HPGe

Cd


Background suppression (1)

besides the passive shielding, additional techniques for background suppression are used:

• No selection (1540663 ev.)• Odd-even coinc. (287778 ev.)• E-window 19-22 keV (4740 ev.)

Data after 8491 hours:


microphonic effect suppression

Matrix + effect of microphonic noise cut

Backgroundsuppression (2)

double shaping technique → scatter plot called ‘matrix’

graphical cut application


Phase I result acquisition with 10g

of 106Cd after 8491 hours:

• data• linear background• Cd X-ray multiplet• excluded Pd X-ray events

%)90(100.2)( 20106/22/1 yCdT ECEC


Phase II preparation (1)238keV area distributionalong the cryostat:


Phase II preparation (2)

Step 1: internal shielding bricks swapped

→ negative

Background source localization and elimination:

Step 2: detectors with holders swapped

→ negative


weld

Phase II preparation (3)Step 3: endcap central part removal

→ positive


Phase II preparation (4)

test measurement with modified endcap – 1 month acquisition:

Spectrum before and after endcap modification

238keV area reduction:

whole cryostat: 5x

four central detector pairs: 13x


T1/2 = 4.4 · 1021 y (Simkovic)

Conclusions, near-term plans

T1/2 = 8.7 · 1020 y (Hirsch)

more enriched material available (15g)

to continue for at least 3 years

factor 10 of improvement is reasonable

Main source of background inside the cryostat localized and removedMain source of background inside the cryostat localized and removed

Phase II is starting:Phase II is starting:

T1/2 = 1.0 · 1020 y (Suhonen)

T1/2 > 2.0 · 1020 y (TGV II)

Main run (1 year duration) with enriched Main run (1 year duration) with enriched 106106CdCd completed in 2006 completed in 2006

Phase I terminated giving new estimation on Phase I terminated giving new estimation on TT1/21/2 (2 (2EC/EC, g.s.EC/EC, g.s.→g.s.→g.s.) ) of of 106106CdCd


1. PhysicsConceptual design study (MC, theoretical calculations, background study) – a) the possibility to measure 2EC/EC decay with other isotopes (162Er, 156Dy) V.Ceron, J.Hirsch, arXiv:nucl-th/9911021v1b) the study of the posibility to measure 0EC/EC decay (152Gd g.s., 112Sn exc. state– resonance enhancement of the 0EC/EC process if Q – Qr < 1 keV)J.Bernabeu, A. deRujula, C.Jarlskog, Nucl. Phys. B223, 15 (1983)Z.Sujkowski, S.Wycech, Phys. Rev. C70, 052501, 2004signature – X-rays < 100 keV + or e-e+ or Majoron advantage: good value of the rates between 0EC/EC and 2EC/EC processes

Future plans (1)


2. Instrumentation

Future plans (2)

How about to use a pixellated detector for EC/EC measurements?(coincidences, position, X-ray energy)

• Planar pixellated detector (Si, GaAs, CdTe, thickness: 300/700/1000m, Ge ~500m)

• Bump-bonded to Medipix readout chip containing amplifier, double discriminator, and counter in each pixel cell

Medipix2 andTimePixPixels: 256 x 256Pixel size: 55 x 55 m2

Area: 1.5 x 1.5 cm2

Medipix2 QuadPixels: 512 x 512Pixel size: 55 x 55 m2

Area: 3 x 3 cm2