New limits on + EC and ECEC processes in 74 Se and 120 Te A.S. Barabash 1), F. Hubert 2), Ph. Hubert 2), A. Nachab 2) and V. Umatov 1) 1) ITEP, Moscow,

New limits on +EC and ECEC processes in 74Se and 120Te

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

and V. Umatov1)

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

Outline

Introduction 120Te experiment 74Se experiment 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 (Qmax 0.8 MeV)

(6 nuclei) +EC: Q = M – 2me – b (Qmax 1.8 MeV)

(22 nuclei)

ECEC: Q = M – 2b (Qmax 2.8 MeV)

(34 nuclei)

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); resonance conditions

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 keVQ’(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)

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

Decay-scheme of 74Se

Here M = 1209.7±2.3 keV

Q’ = M - 2Eb

Q’(E*) = Q’ – 1204.2 0

Isotope-candidates (transition to the excited state)

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

74Se 0.89 1209.7±2.3 1204.2 (2+) 11.1 1.2378Kr 0.35 2846.4±2.0 2838.9 (2+) 12.6 1.4796Ru 5.52 2718.5±8.2 2700(?) 20 2.86106Cd 1.25 2770±7.2 2741.0 (1,2+) 24.3 3.33112Sn 0.97 1919.5±4.8 1871.0 (0+) 26.7 3.73130Ba 0.11 2617.1±2.0 2608.4 (?) 34.5 5.10136Ce 0.20 2418.9±13 2399.9 (1+,2+)

2392.1(1+,2+)

37.4 5.62

162Er 0.14 1843.8±5.6 1745.7(1+) 53.8 8.58

g.s.-g.s. transitions

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

(There are only X-rays in this case)

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

[It is possible to improve the accuracy

of M to ~ 200 eV]

II. 120Te [J. Phys.G 34 (2007) 1721]

M = 1700.1 ± 10 keV

= 0.09%

SCHEME OF EXPERIMENT

E = 2.0 keV

(for 1332 keV)

T = 475.4 h

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

120Te (spectra)

120Te (spectra)

120Te (results)

Transition E () T1/2, 1018 y

This work

T1/2, 1018 y

Other works (COBRA)

+EC(0+2); g.s. 511.0 (7.38%) > 0.19 > 0.12 (0)

ECEC(0) L1L2; g.s. 1691.2 (2.05%) > 0.29 > 0.0027 (0)

ECEC(0) K1L2; g.s. 1666.4 (2.08%) > 0.39 > 0.0027 (0)

ECEC(0) K1K2; g.s. 1641.7 (2.08%)

511.0 (7.38%)

> 0.6

> 0.19

> 0.0027 (0)

-

ECEC(2); g.s. - - > 0.0094 (2)

ECEC(0+2); 2+1 1171.26 (2.60%) > 0.75 > 0.0084 (2)

> 0.0097 (0)

Present limits are ~ 1.5-200 times better then previous best results!!!

Future possibilities: 1 kg of 120Te, 1 y ~ 5·1021 y CUORICINO (40 kg of natural Te)

~ 1021 y CUORE (1000 kg of natural Te), COBRA (440 kg

of CdZrTe)

~ 1023-1024 y

[In the last case ECEC(2) transition could be detected]

III. 74Se [Nucl. Phys. A 785 (2007) 371]

97 ` 2.31 2 8

1 2 5

7.2

5.9

1 2 22.2

8

5.8

.2.7

.7 1.7 k

22.4 1.6) ke

M = 1209.7 ± 2.3 keV = 0.89%

400 cm3 HPGe detectorE = 2.0 keV(for 1332 keV)

Mass of Se powder is 563 g

t = 436.56 h

74Se (spectra)

74Se (results)

Transition E, keV T1/2, y (90%CL)

+EC(0+2); g.s. 511.0 > 0.55·1019

ECEC(2); 2+1 595.8 > 0.77·1019

ECEC(2); 2+2 595.8, 608.4, 1204.2 > 0.55·1019

ECEC(0) L1L2; g.s. 1206.9 > 0.41·1019

ECEC(0) K1L2; g.s. 1197.2 > 0.64·1019

ECEC(0) K1K2; g.s. 511

1185.9

> 0.19·1019

> 0.62·1019

74Se (results-2)

Transition E, keV T1/2, y (90%CL)

ECEC(0) L1L2; 2+1 595.8, 611.1 > 1.3·1019

ECEC(0) K1L2; 2+1 595.8, 601.4 > 1.12·1019

ECEC(0) K1K2; 2+1 595.8, 590.1 > 1.57·1019

ECEC(0) L1L2; 2+2 595.8, 608,4,

1204.2> 0.55·1019

How to increase the sensitivity:

1 kg of 74Se, 1 y ~ 5·1021 y 200 kg of 74Se (using GERDA or

MAJORANA), 10 y ~ 1026 y (<m> ~ 0.1 eV).

CONCLUSION New limits on the +EC and ECEC processes

for 120Te have been obtained (limits are in ~ 1.5-200 times better than previous results)

For the first time limits on +EC and ECEC processes for 74Se have been obtained

For the first time possible resonance ECEC(0) transition 74Se-74Ge (1204.2 keV) has been investigated and limit 5.5·1018 y was obtained

BACKUP SLIDES

Last best achievements for such processes ECEC(2):

- T1/2(130Ba) = (2.2 ± 0.5)·1021 y (geochemical) - > 1.5·1021 y (78Kr, Baksan) - > 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)

Table 7. Best present limits on ECEC(0) to the excited state (for isotope-candidates with

possible resonance conditions)

Nuclei E*(Jf) T1/2, y

106Cd 2741 (1,2+) > 3·1019 [DAMA-Solotvino]> 5·1019 *) [TGV-II]

74Se 1204.2(2+) > 0.55·1019 [This work]

130Ba 2608.4(?) > 1.5·1021 (geochemical)

78Kr 2838.9(2+) > 1.2·1021 *) [Baksan]

*) Extracted from result for 2(0+-0+g.s.) transition