Search for double beta decay of

Search for double beta decay of 106 Cd with TGV-2 spectrometer

N.I.Rukhadze (JINR, Dubna) on behalf of TGV collaboration

JINR Dubna, Russia

IEAP, CTU Prague, Czech Republic CU Bratislava, Slovakia

LSM Modane, France

TAUP 2021, Valencia, Spain,

26 August - 3 September 2021

SEARCH FOR DOUBLE BETA DECAY

 At present 2 ν 2 β ¯ decay was detected in 11 nuclei:

48

Ca,

Ge,

Se,

Zr,

Mo,

Cd,

Te,

Te,

Xe,

Nd,

U

“Positive” results in search for 2νEC/EC decay

• 2 ν EC/EC in

Ba was detected in geochemical experiment (A.P.Meshik et al..

Phys. Rev. C 64 , 2001, 035205).

• The indication on 2 ν EC/EC in

Kr (Yu.M.Gavrilyuk et al., Phys. Rev. C 87 , 2013, 035501),

• 2 ν EC/EC in

Xe (XENON1T collaboration, 2019)

DOUBLE BETA DECAY OF 106 Cd

EC/EC 2e

- +

Cd →

Pd + (2 ν

) + ( γ )

Experimental signature (TGV-2): 2KXPd (+ γ for e.s.) β+/EC e

- +

Cd →

Pd + e+ + (2 ν

) + ( γ )

Experimental signature (TGV-2) : KXPd + 2 γ 511 (+ γ for e.s.) β+β+

Cd →

Pd + e

+ e

+ (2 ν

) + ( γ )

Experimental signature (TGV-2) : 4 γ 511 (+ γ for e.s.)

Experiment TGV-2

Telescope Germanium Vertical Laboratoire Souterrain de Modane, France

Phase I ~ 10g (12 samples) of 106 Cd (75%), ~ 3.2 g (4 samples) of Cd-nat. (~ 4.25 x 10 22 atoms of 106 Cd) T= 8687h

(Feb.2005 – Feb.2006)

Phase II ~ 13.6 g (16 samples) of 106 Cd (75%) (~ 5.8 x 10 22 atoms of 106 Cd) T = 12900h

(Dec.2007 – July 2009)

Background I no samples (Aug.2009 – Mar.2010)

Background II 16 samples of Cd.-nat (April 2010 -Nov.2013) Phase III ~ 23.2 g (16 samples) of 106 Cd (99.57%) (~ 1.3 x 10 23 atoms of 106 Cd) T >42500 h

(Feb.2014 – Sep.2015, Apr.2016 – …..) in progress

106 Cd

106 Ag

106 Pd

0

0

0

2

1133.8

511.9

γ 51 1. 9 γ 622 Q(EC/EC) = 2775.39 ± 0.10 keV 1.25%

1

2νEC/EC (0 + g.s. –0 + g.s. ) 2KX Pd (~21 keV)

2741.0 4

γ 2229 γ 2741

1557.7 2717.6 3

γ 1046 γ 1160 β + β +

β +/EC EC/EC

0 ν EC/EC Resonant Decay of

Cd

Q= 2775.39±0.10 keV, E

=24.3 keV, E

=3.33 keV

E*

= 2741.0 keV KL observables γ – 2741 (2229+512) keV E*

= 2717.6 keV KK observables γ – ( 1160 + 1046 + 512) keV E*

= 2737 keV (?) KL observables γ – ?

Phase III - Search for 0 ν EC/EC decay of

Cd → Obelix det.

Telescope Germanium Vertical (TGV-2)

32 HPGe planar detectors ∅ 60 mm x 6 mm with sensitive volume: 20.4 cm

x 6 mm

Total sensitive volume: ~400 cm

Total mass of detectors: ~3 kg Total area of samples : 330 cm

Total mass of sample(s) : 10 ÷ 25 g Total efficiency : 50 ÷ 70 %

E-resolution : 3 ÷ 4 keV @

Co LE-threshold : 5 ÷ 6 keV

Double beta emitters:

16 samples (~70µm) of

Cd (enrich.99.57%)

~23.2 g (~ 1.3 x 10

atoms) of

Cd

Distance from foils to detectors is ≤1.5 mm

HPGe HPGe

Cd

106 Cd

Detectors and foils of TGV-2

16 circle foils:

thickness = 70±10 mg/cm

diameter = 52 mm

mass = 23.166 g

enrichment= 99.57%.

PASSIVE SHIELDING

Copper

> 20 cm

Airtight box

> 10 cm Lead

Polyethylene filled with boron 16 cm

Modane Underground Laboratory, France

(4800 m w.e.)

4 muons /day / m

Copper shielding

Airtight box

shielding Lead

Neutron shielding shielding Lead

Tube for calibration

source

TGV-2 Passive

shielding

Background suppression

• Construction

– Radiopure materials

– Minimization of amount of construction materials

• Electronics

– telescopic construction (double coincidences from neighboring detectors)

– double-shaping selection of low energy events

• Passive shielding

– Modane Underground Laboratory

– Pb + Cu

– airtight box against radon

– anti-neutron shielding (borated polyethylene)

Suppression of microphonic noise

2µs

8µs

Laboratoire Souterrain de Modane

Fréjus Tunnel at the French-Italian border

Depth - 1800 m of rock (4800 mwe) Muons flux - 4 muons / m

x day

(2x10

reduction factor) Neutrons flux - 3000 fast neutrons (>1MeV) per m

and per day

(1000 reduction factor)

KXPd

KXPd

KXCd

KXCd

ROI ROI

ROI ROI

Phase II, 13.6g of 106 Cd, T=12900h

KXCd

Pb X-rays

Cs-137 661 keV Bi-214

609 keV Tl-208

583 keV 511 keV

Pb-214 352 keV Pb-214

295 keV Pb-212

238 keV Ra-226

186 keV

Single Double

Double+KXPd

Single, Double and Double+KXPd energy spectra of TGV-2

KK TGV signal patterns β + β +

ΚΚ -pair

E

E

E

E

E

E

E

E

E

+E

= γ

γ

γ

γ D -paired

E E

= γ

γ D -single

E

=E

= K

(ΚΚ+γ

)-pair

E

E

γ

1.

(ΚΚ) -pair +

γ

-satellite (single or paired)

E

E

γ

2.

γ

E

E

E

E

E

+E

=511 keV

γ

γ γ 511 -paired

E

=511 keV E

γ 511 -single

E

<511 keV E

γ 511 -fired ββ -pair

candidate

E

E

E

E

ββ -pair + γ -satellite (single, paired, or fired)

E

E

γ

E

+E

!= 511 keV

Two types of TGV-2 analysis to find possible KXPd-KXPd events*

* N.I. Rukhadze et al. / Nuclear Physics A 852 (2011) 197–206

1D method 2D method

A signal in the 19–22 keV energy window in one detector, while a signal from another face-to-face neighbor detector was collected in another. A final accumulated spectrum was fitted with a 1D-model which included the KXPd multiplet as signal, and the Cadmium KX-ray (KXCd) multiplet with linear underlay as background.

The double coincidence events from neighboring face-to-face detectors, both in the 16–30 keV energy range, were collected in a 2Dhistogram.

The final 2D-spectrum was fitted by a 2D-model consisting of the 2D-Gaussian KXPd multiplet as signal, and the KXCd 2D-Gaussian multiplet together with the 2D-background slope as background

КК-spectra in the ROI (19-22 keV)

1D method 2D method

2 mks

8 mks

KXPd

KXPd

KXCd

KXCd

Decay

mode Final level

of

Pd T

, y (90%CL)

Phase II* T

, y (90%CL) Phase III 2νEC/EC 0

g.s. 4.2 × 10

7.2 × 10

2

, 511.9 keV 1.2 × 10

8.9 × 10

0

, 1134 keV 1.0 × 10

7.2 × 10

0νEC/EC 2717.6 keV 1.6 × 10

1.4 × 10

0νEC/EC 4

, 2741 keV 1.8 × 10

0.9 × 10

2νβ

/EC 0

g.s. 1.1 × 10

6.6 × 10

2

, 511.9 keV 1.1 × 10

7.6 × 10

0

, 1134 keV 1.6 × 10

9.0 × 10

2νβ

β

0

g.s. 1.4 × 10

3.9 × 10

2

, 511.9 keV 1.7 × 10

4.7 × 10

TGV-2 limits on double beta decay of 106 Cd

*N.I.Rukhadze et al., Journal of Physics: Conference Series 375 (2012) 042020

T

theor. ( 2νEC/EC) ~ 10

– 10

Obelix

Obelix

Thank you for attention