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, Russia 2) CENBG, Gradignan, France 1

Outline  Introduction  120 Te experiment  74 Se experiment  Conclusion

I. Introduction 2  +,  + EC and ECEC processes:  0 -transitions: (A,Z)  (A,Z-2) + 2e + e b + (A,Z)  (A,Z-2) + e + + X 2e b + (A,Z)  (A,Z-2) +  (2 ,e + e -,e -,…) + 2X  2 -transitions: (A,Z)  (A,Z-2) + 2e e b + (A,Z)  (A,Z-2) + e X 2e b + (A,Z)  (A,Z-2) X

Q value  2  + : Q =  M – 4m e – 2  b (Q max  0.8 MeV) (6 nuclei)   + EC: Q =  M – 2m e –  b (Q max  1.8 MeV) (22 nuclei)  ECEC: Q =  M – 2  b (Q max  2.8 MeV) (34 nuclei)

ECEC(0 ) to the ground state  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)139.

ECEC(0 ); resonance conditions Transition to the ground state. For the best candidates ( = 1 eV):  +  + (0 ) ~ y  + EC(0 ) ~ y ECEC(0 ) ~ y (One can compare these values with ~ 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 112 Sn (transition to 0 + excited state). It was shown that enhancement factor can be on the level ~ 10 6 !

J. Bernabeu, A. De Rujula, C. Jarlskog, Nucl. Phys. B 223 (1983) Sn  112 Cd [0 + (1871)] M = ±4.8 keV Q’(KK;0 + ) = M – E*(0 + ) – 2E K = = (-4.9 ± 4.8) keV T 1/2 (0)  3·10 24 y (for = 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 keV)

Resonance conditions  In 2004 the same conclusion was done by Z. Sujkowski and S. Wycech (Phys. Rev. C 70 (2004) ).  Resonance condition (using single EC(,) argument): E brems = 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 74 Se Here M = ±2.3 keV Q’ = M - 2E b Q’(E*) = Q’ –  0

Isotope-candidates (transition to the excited state) NucleiA, %  M, keV E*, keVEKEK E L2 74 Se ± (2 + ) Kr ± (2 + ) Ru ± (?) Cd ± (1,2 + ) Sn ± (0 + ) Ba ± (?) Ce ± (1 +,2 + ) (1 +,2 + ) Er ± (1 + )

g.s.-g.s. transitions 152 Gd (0.2%), 164 Er (1.56%), 180 W(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. 120 Te [J. Phys.G 34 (2007) 1721] M = ± 10 keV  = 0.09%

SCHEME OF EXPERIMENT E = 2.0 keV (for 1332 keV) T = h Experiment is done in Modane Underground Laboratory, 4800 m w.e.

120 Te (spectra)

120 Te (results) Transition E  (  ) T 1/2, y This work T 1/2, y Other works (COBRA)  + EC(0 +2 ); g.s (7.38%)> 0.19 > 0.12 (0 ) ECEC(0 ) L 1 L 2 ; g.s (2.05%)> 0.29 > (0 ) ECEC(0 ) K 1 L 2 ; g.s (2.08%)> 0.39 > (0 ) ECEC(0 ) K 1 K 2 ; g.s (2.08%) (7.38%) > 0.6 > 0.19 > (0 ) - ECEC(2 ); g.s. -- > (2 ) ECEC(0 +2 ); (2.60%)> 0.75 > (2 ) > (0 ) Present limits are ~ times better then previous best results!!!

Future possibilities:  1 kg of 120 Te, 1 y  ~ 5·10 21 y  CUORICINO (40 kg of natural Te)  ~ y  CUORE (1000 kg of natural Te), COBRA (440 kg of CdZrTe)  ~ y [In the last case ECEC(2 ) transition could be detected]

III. 74 Se [Nucl. Phys. A 785 (2007) 371] M = ± 2.3 keV  = 0.89% 400 cm 3 HPGe detector E = 2.0 keV (for 1332 keV) Mass of Se powder is 563 g t = h

74 Se (spectra)

74 Se (results) TransitionE , keVT 1/2, y (90%CL)  + EC(0 +2 ); g.s > 0.55·10 19 ECEC(2 ); > 0.77·10 19 ECEC(2 ); , 608.4, > 0.55·10 19 ECEC(0 ) L 1 L 2 ; g.s > 0.41·10 19 ECEC(0 ) K 1 L 2 ; g.s > 0.64·10 19 ECEC(0 ) K 1 K 2 ; g.s > 0.19·10 19 > 0.62·10 19

74 Se (results-2) TransitionE , keVT 1/2, y (90%CL) ECEC(0 ) L 1 L 2 ; , 611.1> 1.3·10 19 ECEC(0 ) K 1 L 2 ; , 601.4> 1.12·10 19 ECEC(0 ) K 1 K 2 ; , 590.1> 1.57·10 19 ECEC(0 ) L 1 L 2 ; , 608,4, > 0.55·10 19

How to increase the sensitivity:  1 kg of 74 Se, 1 y  ~ 5·10 21 y  200 kg of 74 Se (using GERDA or MAJORANA), 10 y  ~ y ( ~ 0.1 eV).

CONCLUSION  New limits on the  + EC and ECEC processes for 120 Te have been obtained (limits are in ~ times better than previous results)  For the first time limits on  + EC and ECEC processes for 74 Se have been obtained  For the first time possible resonance ECEC(0) transition 74 Se- 74 Ge ( keV) has been investigated and limit 5.5·10 18 y was obtained

BACKUP SLIDES

Last best achievements for such processes  ECEC(2 ): - T 1/2 ( 130 Ba) = (2.2 ± 0.5)·10 21 y (geochemical) - > 1.5·10 21 y ( 78 Kr, Baksan) - > 2·10 20 y ( 106 Cd, TGV-II) - > 5.9·10 21 y ( 40 Ca, DAMA-Solotvino)  2  + (0 +2 ), EC  + (0 +2 ), ECEC(0 ): > y ( 78 Kr, 106 Cd, 40 Ca; Baksan-Spain, DAMA-Solotvino) > y ( 120 Te, 108 Cd, 136 Ce, 138 Ce, 64 Zn, 180 W; COBRA, DAMA, Solotvino)

Table 7. Best present limits on ECEC(0) to the excited state (for isotope-candidates with possible resonance conditions) NucleiE*(J  f )T 1/2, y 106 Cd2741 (1,2 + )> 3·10 19 [DAMA-Solotvino] > 5·10 19 *) [TGV-II] 74 Se1204.2(2 + )> 0.55·10 19 [This work] 130 Ba2608.4(?)> 1.5·10 21 (geochemical) 78 Kr2838.9(2 + )> 1.2·10 21 *) [Baksan] *) Extracted from result for 2( g.s. ) transition