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DOUBLE BETA DECAY TO THE EXCITED STATES (EXPERIMENTAL REVIEW). A.S. BARABASH ITEP, MOSCOW. OUTLINE. Introduction 2 - (2) -decay to the excited ststates - 100 Mo - 150 Nd 2 - (0) –decay to the excite states ECEC to the excited states Conclusion. I. Introduction.
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DOUBLE BETA DECAY TO THE EXCITED STATES (EXPERIMENTAL REVIEW) A.S. BARABASH ITEP, MOSCOW
OUTLINE • Introduction • 2-(2)-decay to the excited ststates - 100Mo - 150Nd • 2-(0)–decay to the excite states • ECEC to the excited states • Conclusion
1.1. Historical introduction E. Fiorini (1977, NEUTRINO’77) – first time obtained limit on 0+-2+ decay in Ge-76 (as by-product for 0+-0+ transition)*): T1/2(0)> 3·1021 y (68% C.L.) *) Of course, from geochemical experiments one can extract limits too.
1982 – first special experimental work to investigate 2-decay to the excited states was done: E. Bellotti et al., Lett. Nuov. Cim. 33 (1982) 273. (58Ni, 76Ge, 92Mo, 100Mo, 148Nd, 150Nd; Transitions to 2+1, O+1, 2+2, … excited states) Limits on the level (1.2-3.2)·1021 y for 76Ge and ~ 1018-1019 y for other nuclei were obtained.
1983-1988 • Many new results for 76Ge (0+-2+). And even “evidence” of the decay on 2.5 level (T1/2 1022 y) have been obtained. • 3 experiments were done by E. Norman (50Cr, 58Ni, 64Zn, 92Mo, 94Zr, 96Zr, 96Ru, 106Cd, 116Cd, 124Sn; natural samples). Limits on the level ~ 1017-1019 y were obtained.
1989-1990 • It was demonstrated that 2(2;0+-0+1)-decay can be detected in 100Mo, 96Zr and 150Nd by existing low-background HPGe detectors and new experiments were proposed (A.S.B. preprint ITEP, 188-89, 1989; JETP Lett. 51 (1990) 207). • ITEP-USC-PNL-UM experiment with 1 kgof 100Mo was started on 30 May 1990 (in Soudan mine).
Measurement was stopped in September’91 • First “positive” result was reported at a few International Conferences (Moriond’91, TAUP’91, WEIN’92,…) • Final result was published in 1995 [PL B 345 (1995) 408]: T1/2 = 6.1+1.8-1.1·1020 y
1999 – 2-nd positive result for100Mo; 2001 – 3-d positive result for 100Mo (in ITEP-TUNL experiment); 2004 – 1-st positive result for 150Nd; 2007 – 4-th positive result for 100Mo (in NEMO-3 experiment).
1.2. Present motivation • Nuclear spectroscopy • NME problem • Checking of some “creasy” ideas ( “bosonic” neutrino, …) • 0-decay: - very nice signature (2-); - high sensitivity (ECEC; resonance conditions).
II. 2-(2)-decay to the excited states Table 1. 2 transition to 2+1 excited state.
References [1] A.A. Raduta and C.M. Raduta, Phys. Lett. B 647 (2007) 265. [2] M. Aunola and J. Suhonen, Nucl. Phys. A 602 (1996) 133. [3] J. Toivanen and J. Suhonen, Phys. Rev. C 55 (1997) 2314. [4] S. Stoica and I. Mihut, Nucl. Phys. A 602 (1996) 197. [5] J.G. Hirsch et al., Phys. Rev. C 51 (1995) 2252.
Table 3.Present “positive” results on 2(2) decay of 100Mo to the first 0+ excited state of 100Ru Average value: 6.2+0.9-0.7·1020 y
References [6] A.S. Barabash et al., Phys. Lett.B 345 (1995) 408. [7] A. S. Barabash et al., Phys. At. Nucl. 62 (1999) 2039. [8] L. De Braeckeleer et al., Phys. Rev. Lett. 86 (2001) 3510. [9] M.J. Hornish et al., Phys. Rev. C 74 (2006) 044314. [10] R. Arnold et al., Nucl. Phys. A 781 (2007) 209.
0+ 100Mo 3034 keV 41+ (1227 keV) g2 01+ (1130 keV) 21+ (540 keV) 22+ (1362 keV) g1 0+ (g.s.) 100Ru NEMO-3100Mo: bb decay to exc. states NEMO-3; 334.3 days of data (Phase I) 2nbb decay to the 01+ state: S/B = 3.0 T1/2 =[ 5.7+1.3-0.9(stat) ± 0.8(syst)]1020 y 0nbb decay to the 01+ state: T1/2 > 8.9 1022 y@ 90 % C.L. 2nbb decay to the 21+ state: T1/2 > 1.1 1021 y @ 90 % C.L. 0nbb decay to the 21+ state: T1/2 > 1.6 1023 y@ 90 % C.L. Nucl. Phys. A 781 (2007) 209 Clear topology: 01+: 2e- + 2g in time & energy and TOF cuts 21+: 2e- + 1g in time & energy and TOF cuts
TOP VIEW SIDE VIEW e1 2 e1 e2 1 2 1 e2 100Mo (NEMO-3) Reconstructed event-candidate
100Mo (NEMO-3) The main characteristics of selected events
0+ 150Nd 3367 keV 41+ (773.3 keV) g2 01+ (740.4 keV) 21+ (333.9keV) 22+ (1046.1 keV) g1 0+ (g.s.) 150Sm 150Nd Decay scheme E1 = 333.9 keV E2 = 406.5 keV
SCHEME OF EXPERIMENT E = 1.9 keV (for 1332 keV) T = 11320.5 h Experiment is done in Modane Underground Laboratory, 4800 m w.e.
150Nd. Transition to the 0+ excited state T1/2 = [1.4+0.4-0.2(stat) ± 0.3(syst)]·1020 y [JETP. Lett. 79 (2004) 10]
Comparison of NME for transition to the 0+ ground and 0+1excited states (for 100Mo and 150Nd) • Conclusion is NME(g.s.) NME(0+1) • But, in fact, it looks like: NME(g.s.) (1.2-1.3)xNME(0+1)
III. 2(0)-decay to excited states Very nice signature: 2e- and two (one) gamma with fixed energy Possibility to have “zero” background Possibility to have high sensitivity (if registration efficiency and energy resolution are high enough)
3.1. 2(0)-decay to 2+1 excited state Many years people thought that this decay is sensitive only to right-handed currents. T. Tomoda demonstrated that this is not through: “…relative sensitivity of 0+-2+ decays to the neutrino mass and the right-handed currents are comparable to those of 0+-0+ decays.” [T. Tomoda, Phys. Lett. B 474 (2000) 245] The decay is suppressed in ~ two order of magnitude in comparison to transition to 0+g.s.
Table 4. Best present limits on 2(0)-decay to 2+1 excited state
Table 5. Best present limits on 2(0)-decay to the 0+1excited state
Table 5. (Continue) *) For <m> = 1 eV [11] J. Suhonen, Phys. Lett. B 477 (2000) 99. [12] J. Suhonen, Phys. Rev. C 62 (2001) 042501. [13] J. Suhonen, Nucl. Phys. A 700 (2002) 649. [14] J. Suhonen and M. Aunola, Nucl. Phys. A 723 (2003) 271. [15] F. Simkovic et al., Phys. Rev. C 64 (2001) 035501.
2(0)-decay to 0+1excited state • Future possibilities: - MAJORANA and GERDA with 76Ge ~ 1027 y; - CUORE with 130Te ~ 1026 y; - SuperNEMO with 82Se (or 150Nd) ~ 1024-1025 y;
IV. ECEC to the excited states • 1994 (A.S.B. JETP Lett. 59 (1994) 677). Main assumption: NME(2; 0+g.s. ) NME(2; 0+1): then T1/2(0+1) ~ 1021-1022 y for 96Ru, 106Cd, 124Xe, 136Ce; ~ 1023 y for 78Kr and 130Ba Very nice signature: in addition to two X-rays we have here two gamma with strictly fixed energy (E ~ 300-1300 keV) New experiments were proposed
Table 6. Best present limits on ECEC(2) to the 0+1 excited state *) Extracted from geochemical experiment **) Extracted from result for 0+-0+g.s. transition
IV.2. ECEC(0); resonance conditions Transition to the ground state. For the best candidates (<m> = 1 eV): ++ (0) ~ 1028-1030 y +EC(0) ~ 1026-1027 y ECEC(0) ~ 1028-1031 y (One can compare these values with ~ 1024-1025 y for 2--decay)
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 comparison with EC+(0)) – M. Doi and T. Kotani, Prog. Theor. Phys. 89 (1993)139.
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, E-energy of excited state) • In 1982 the same idea for transition to ground and excited 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 Q’(KK;0+) = M – E*(0+) – 2EK = = (-4.9 ± 4.8) keV T1/2 3·1024 y (for m = 1 eV) (if Q’ ~ 10 eV)
Resonance conditions • In 2004 the same conclusion was done by Z. Sujkowski and S. Wycech (Phys. Rev. C 70 (2004) 052501). Resonance condition (using EC(2) arguments): 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 Q = M = 1209.7 keV Q’ = M - 2Eb Q’(E*) = Q’ – 1204.2
74Se.(Nucl. Phys. A 785 (2007) 371) • 400 cm3 HPGe detector (Modane Underground Laboratory; 4800 m w.e.) • 563 g of natural Se (4.69 g of 74Se) • Measurement time is 436.56 h
74Se.(Nucl. Phys. A 785 (2007) 371) Transition to 2+2(1204.2 keV) state (595.8 keV and 608.4 keV lines were investigated): T1/2(0;L1L2) > 0.55·1019 y
74Se. Possible improvements • 1 kg of 74Se ~ 3·1021 y • 200 kg of 74Se (using an installation such as GERDA or MAJORANA) ~ 1026 y
Table 7. Best present limits on ECEC(0) to the excited state (for isotope-candidates with possible resonance conditions) *) Extracted from result for 2(0+-0+g.s.) transition