Search for +EC and ECEC processes in 112Sn

A.S. Barabash1), Ph. Hubert2), A. Nachab2)

and V. Umatov1)

1) ITEP, Moscow, Russia2) CNBG, Gradignan, France

Outline

Introduction Experiment Results Conclusion

I. Introduction

2+, +EC and ECEC processes:

0-transitions: (A,Z) (A,Z-2) + 2e+

eb + (A,Z) (A,Z-2) + e+ + X

2eb + (A,Z) (A,Z-2) + (2,e+e-,e-,…) + 2X 2-transitions: (A,Z) (A,Z-2) + 2e+ + 2 eb + (A,Z) (A,Z-2) + e+ + 2 + X

2eb + (A,Z) (A,Z-2) + 2 + 2X

Q value

2+: Q' = M – 4me – 2b (Q'max 0.8 MeV) (6 nuclei) +EC: Q' = M – 2me – b (Q'max 1.8 MeV)

(22 nuclei) ECEC: Q' = M – 2b (Q'max 2.8 MeV) (34 nuclei)

[ Q(2-) 3 MeV ]

ECEC(0) to the ground state 2eb + (A,Z) (A,Z-2) + 2X + brem

+ 2 + e+e-

+ e-int

E,.. = M - e1 -e2

Suppression factor is ~ 104 (in comparisonwith EC+(0)) – M. Doi and T. Kotani, Prog. Theor. Phys. 89 (1993)139.

ECEC(0)

Transition to the ground state. For the best

candidates (<m> = 1 eV):

++ (0) ~ 1028-1030 y+EC(0) ~ 1026-1027 yECEC(0) ~ 1028-1031 y

(One can compare these values with ~ 1024-1025 y for 2--decay)

Resonance conditions In 1955 (R.Winter, Phys. Rev. 100 (1955) 142) it was mentioned

that if there is excited level with “right” energy then decay rate can be very high.

(Q’-E* has to be close to zero. Q’-energy of decay to g.s., E*-energy of excited state)

In 1982 the same idea for transition to excited and ground states was discussed (M. Voloshin, G. Mizelmacher, R. Eramzhan, JETP Lett. 35 (1982)).

In 1983 (J. Bernabeu, A. De Rujula, C. Jarlskog, Nucl. Phys. B 223 (1983) 15) this idea was discussed for 112Sn (transition to 0+ excited state). It was shown that enhancement factor can be on the level ~ 106!

J. Bernabeu, A. De Rujula, C. Jarlskog, Nucl. Phys. B 223 (1983) 15

112Sn 112Cd [0+(1871)] M = 1919.5±4.8 keV (old value)Q’(KK;0+) = M – E*(0+) – 2EK = = (-4.9 ± 4.8) keV

T1/2 (0) 3·1024 y (for <m> = 1 eV)(if Q’ ~ 10 eV) [ECEC(2) transition is strongly suppressed!!!]

Nice signature: in addition to two X-rays we have here two gamma-rays with strictly fixed energy (617.4 and 1253.6 keV)

J. Bernabeu, A. De Rujula, C. Jarlskog, Nucl. Phys. B 223 (1983) 15

112Sn112Cd(0+;1870 keV)

The ECEC(0) mode is shownas a function of the degeneracyparameter Q-E

Resonance conditions In 2004 the same conclusion was done by

Z. Sujkowski and S. Wycech (Phys. Rev. C 70 (2004) 052501).

Resonance condition (using single EC(,)argument):Ebrems = Q’res = E(1S,Z-2)-E(2P,Z-2)

(i.e. when the photon energy becomes comparable to the 2P-1S level difference in the final atom)

Q’-Q’res < 1 keV

Z. Sujkowski and S. Wycech

Decay-scheme of 112Sn

Here M = 1919.82±0.16 keV

(PRL 103 (2009) 042501)

Q’ = M - 2Eb = 1866.42 keV

Q’(E*) = Q’–1871.137(72)

- 4.71±0.23 keV

Isotope-candidates (transition to the excited state)

Nuclei A, % M, keV E*, keV , keV EK*) EL2

*)

74Se 0.89 1209.7±2.3

1209.240±0.007 (new!)

1204.2 (2+) 2.5±0.1 (LL) 11.1 1.23

78Kr 0.35 2846.4±2.0 2838.9 (2+?) 4.5±2.1 (LL) 12.6 1.47

96Ru 5.52 2718.5±8.2 2700.2 (2+) -4.5±8.2 (KL)

2712.68 (?) 0±8.2 (LL)

20 2.86

106Cd 1.25 2770±7.2 2741.0 (4+) 1.1±7.2 (KL)

2748.2 (2,3) -5.6±7.2 (KL)

24.3 3.33

112Sn 0.97 1919.5±4.8

1919.82±0.16 (new!)

1871.137 (0+) -4.7±0.23 (KK)

1870.74(4+) -4.3±0.21 (KK)

26.7 3.73

130Ba 0.11 2617.1±2.0 2608.42 (?) -1.2±2.0 (LL)

2544.43 (?) 3.7±2 (KK)

34.5 5.10

136Ce 0.20 2418.9±13 2399.87 (1+,2+?) 7.5±13 (LL)

2392.1 (1+,2+?) - ??? -16±13 (KL)

2390.79(3) -14.6±13 (KL)

37.4 5.62

162Er 0.14 1843.8±5.6 1745.7(1+) -9.5±5.6 (KK)

1782.68(2+) -1±5.6 (KL)

53.8 8.58

*)EK and EL2 are given for daughter nuclei 2+: suppression factor is ~ 104

g.s.-g.s. transitions

152Gd (0.2%), 164Er (1.56%),180W(0.13%)

(There are only X-rays in this case)

0+G.S.-0+

G.S.

152Gd-152Sm M = 54.6±3.5 keV =0±3.5 keV K – 46.8 keV (KL case) L1 = 7.73; L2 = 7.31; L3 = 6.71 keV

164Er-164Dy M = 23.3±5.5 keV =5.7±3.9 keV

K – 53.78 keV (LL case) L1 = 9.05; L2 = 8.58; L3 = 7.79 keV

180W-180Hf M = 144.4±6.1 keV =13.7±4.5 keV K – 65.34 keV KK -? L1 = 11.27; L2 = 10.74; L3 = 9.56 keV 180W-180Hf(2+;93.32 keV) M = 51.08±6.1 keV

Problems There is no good theoretical description of the ECEC

processes and “resonance” conditions Accuracy of M (and Q as a result) is not very good (~ 2-

10 keV) and has to be improved Quantum numbers are not known in some cases

[It is possible to improve the accuracy of M to ~ 10-100 eV: 112Sn: M = 1919.82±0.16 keV, PRL 103 (2009) 042501;74Se: M = 1209.240±0.007 keV, PRC 81 (2010) 032501R

M = 1209.169±0.049 keV, PLB 684 (2010) 17]

List of needed M measurements

Priority #1: 152Gd-152Sm, 130Ba-130Xe, 96Ru-96Mo,

Priority #2: 164Er-164Dy, 162Er-162Dy, 136Ce-136Ba,

106Cd-106Pd

II. EXPERIMENT

M = 1919.82 ± 0.16 keV

= 0.97%

SCHEME OF EXPERIMENT

E = 2.0 keV

(for 1332 keV)

T = 3175.23 h

Experiment is done in Modane Underground Laboratory, 4800 m w.e.

100 g of 112Sn;Enrichment is 94.3% 5.05·1023 nuclei

380 cm3 low-background HPGe detector

112Sn (spectra)

Efficiency: 4.61% (617.5 keV) and 2.83% (1253.4 keV)

112Sn (spectra)

112Sn (results) Transition

T1/2, 1020 y

This work Previous work [1] T1/2th(2), y [2]

+ЕС(0+2); g.s. > 0.97 > 0.56 3.81024

+ЕС(0+2); 2+1 > 7.02 > 2.79 2.31032

ECEC(0) L1L2; g.s. > 6.43 > 4.10

ECEC(0) K1L2;g.s. > 8.15 > 3.55

ECEC(0) K1K2;g.s. > 10.63 > 3.97

ECEC(0); 2+1 > 9.72 > 3.93

ECEC(0); 0+1 > 12.86 > 6.87

ECEC(0); 2+2 > 8.89 > 3.45

[1] A.S.B. et al., PRC 80 (2009) 035501; [2] P. Domin et al., NPA 753 (2005) 337.

112Sn (results-2)ECEC(0); 0+

2 > 6.86·1020 > 2.68·1020

ECEC(0); 2+3 > 6.46 > 2.64

ECEC(0); 0+3 > 13.43 > 4.66

ECEC(2); 2+1 > 11.94 > 4.84 4.91028

ECEC(2); 0+1 > 16.25 > 8.67 7.41024

ECEC(2); 2+2 > 11.24 > 4.39 1.91032

ECEC(2); 0+2 > 8.64 > 3.43

ECEC(2); 2+3 > 8.19 > 3.40 6.21031

ECEC(2); 0+3 > 13.43 > 4.66 5.41034

How to increase the sensitivity:

1 kg of 112Sn, 1 y ~ 1022 y 200 kg of 112Sn (using GERDA or

MAJORANA), 10 y ~ 1026 y .

Comparison of existing experimental results for 112Sn-112Cd(1871 Kev) transition

> 1.61018 y (J. Dawson et al., 2008; 1.2 kg of natural Sn) > 0.921020 y (A.S.B. et al., 2008; 4 kg of natural Sn) > 0.81019 y (J. Dawson et al., 2008; 1.2 kg of natural Sn)

> 1.31019 y (M. Kidd et al., 2008; 3.9 g of 112Sn) > 4.71020 y (A.S.B. et al., 2009; 50 g of 112Sn) > 1.31021 y (A.S.B. et al., 2010; 100 g of 112Sn)

Table. Best present limits on ECEC(0) to the excited state (for isotope-candidates with possible resonance conditions)

Nuclear (natural abundance)

E*(Jf) T1/2, y Experiment, year

74Se (0.89%) 1204.20 (2+) > 5.5·1018 Modane (ITEP-Bordeaux), 2007

78Kr (0.35%) 2838.49 (2+) > 1.2·1021 *) Baksan (INR), 2010

96Ru (5.54%) 2700.21 (2+)2712.68 (?)

> 4.9·1018

> 1.3·1019

Gran Sasso(DAMA-Kiev), 2009

106Cd (1.25%) 2741.0 (4+)2748.2 (2,3-)

> 1.7·1020 TGV-II, 2010

112Sn (0.97%) 1871.13 (0+)1870.74 (4+)

> 1.3·1021

> 1.1·1021

Modane (ITEP-Bordeaux), 2010

130Ba (0.106%) 2608.4 (?)2544.43 (?)

> 1.5·1021 *) Geochemical, 2001

136Ce (0.185%) 2399.87 (1,2+)2392.1 (1,2+)

> 4.1·1015

> 2.4·1015

Gran Sasso(DAMA-Kiev), 2009

162Er (0.14%) 1745.7 (1+) - -

*) Estimation from existing experimental data

CONCLUSION New limits on the +EC and ECEC processes for 112Sn

on the level 1020-1021 y have been obtained (limits are in ~ 1.5-3 times better than previous results)

Possible resonance ECEC(0) transition 112Sn-112Cd (1801.13 keV) has been investigated and limit 1.3·1021 y was obtained

New M measurements are needed for other isotope-candidates

Quantum numbers have to be established for 2608.42 and 2544.43 keV levels in 130Xe and 2712.68 kev in 96Mo

BACKUP SLIDES

Last best achievements for such processes ECEC(2):

- T1/2(130Ba) = (2.2 ± 0.5)·1021 y (geochemical) - > 2.4·1021 y (78Kr, Baksan) - > 4.2·1020 y (106Cd, TGV-II) - > 5.9·1021 y (40Ca, DAMA-Solotvino)

2+(0+2), EC+ (0+2), ECEC(0): > 1020-1021 y (78Kr, 106Cd, 40Ca; Baksan-Spain, DAMA-Solotvino) > 1015-1019 y (120Te, 108Cd, 136Ce, 138Ce, 64Zn, 180W; COBRA, DAMA, Solotvino)