F. Cappella INFN-Roma

1. New observation of 2b2n decay of 100Mo to the 0+1 level of 100Ru in the ARMONIA experiment SILAFAE Valparaiso, CHILE 6-12 December 2010 F. Cappella INFN-Roma

2. Roma2,Roma1,LNGS,IHEP/Beijing + by-products and small scale experiments.: INR-Kiev + neutron meas.: ENEA-Frascati + in some studies on bb decays (DST-MAE project): IIT Kharagpur, India DAMA: an observatory for rare processes @LNGS DAMA/R&D low bckg DAMA/Ge for sampling meas. DAMA/LXe measurement with 100Mo DAMA/NaI DAMA/LIBRA http://people.roma2.infn.it/dama

3. DAMA/LXe: results on rare processes • Dark Matter Investigation • Limits on recoils investigating the DMp-129Xe elastic scattering by means of PSD • Limits on DMp-129Xe inelastic scattering • Neutron calibration • 129Xe vs136Xe by using PSD  SD vs SI signals to increase the sensitivity on the SD component NIMA482(2002)728 PLB436(1998)379 PLB387(1996)222, NJP2(2000)15.1 PLB436(1998)379, EPJdirectC11(2001)1 foreseen/in progress • Other rare processes: • Electron decay into invisible channels • Nuclear level excitation of 129Xe during CNC processes • N, NN decay into invisible channels in 129Xe • Electron decay:e-neg • 2bdecay in 136Xe • 2bdecay in 134Xe • Improved results on2bin 134Xe,136Xe • CNC decay 136Xe  136Cs • N, NN, NNN decay into invisible channels in 136Xe Astrop.P.5(1996)217 PLB465(1999)315 PLB493(2000)12 PRD61(2000)117301 Xenon01 PLB527(2002)182 PLB546(2002)23 Beyond the Desert (2003) 365 EPJA27 s01 (2006) 35 DAMA/R&D set-up: results on rare processes DAMA/Ge & LNGS Ge facility • RDs on highly radiopure NaI(Tl) set-up; • several RDs on low background PMTs; • qualification of many materials • measurements with a Li6Eu(BO3)3 crystal (NIMA572(2007)734) • measurements with 100Mo sample investigating  decay in the 4π low-bckg HP Ge facility of LNGS (NPA846(2010)143 ) • search for 7Li solar axions (NPA806(2008)388) •  decay of 96Ru and 104Ru (EPJA42(2009)171) • measurements with a Li2MoO4 (NIMA607(2009) 573) •  decay of 136Ce and 138Ce (NPA824(2009)101) • +Many other meas. already scheduled for near future NPB563(1999)97, Astrop.Phys.7(1997)73 • Particle Dark Matter search with CaF2(Eu) Il N. Cim.A110(1997)189 Astrop. Phys. 7(1997)73 NPB563(1999)97 Astrop.Phys.10(1999)115 NPA705(2002)29 NIMA498(2003)352 NIMA525(2004)535 NIMA555(2005)270 UJP51(2006)1037 • 2 decay in 136Ce and in 142Ce • 2EC240Ca decay • 2 decay in 46Ca and in 40Ca • 2+ decay in 106Cd • 2 and  decay in 48Ca • 2EC2 in 136Ce, in 138Ce • and  decay in 142Ce • 2+ 0, EC + 0 decay in 130Ba • Cluster decay in LaCl3(Ce) • CNC decay 139La 139Ce •  decay of natural Eu •  decay of 113Cd •  decay of 64Zn, 70Zn, 180W, 186W •  decay of 108Cd and 114Cd NPA789(2007)15 PRC76(2007)064603 PLB658(2008)193, NPA826(2009)256 EPJA36(2008)167

4. DAMA results on bbdecay Experimental limits on T1/2 obtained by DAMA (red) and by previous experiments (blue) all the limits are at 90% C.L. (except for 2b+0n in 136Ce and 2b-0n in 142Ce - 68% C.L.) and in 2010: new observation of 2nbb decay of 100Mo to the first excited 0+ level of 100Ru

5. Double beta decay of 100Mo 2b2n decay is allowed in the Standard Model, it is the most rare nuclear decay ever observed in nature, with T1/2 in the range of 1018–1024 yr 2b0n is forbidden in the SM; however, it is predicted by many SM extensions where neutrinos are naturally expected to be Majorana particles with small but non-zero mass Observation of 2b2n decays is also an important tool to test the theoretical models used for the calculations of the nuclear matrix elements for the 2b processes. • 100Mo: one of the most interesting 2b candidates • Natural abundance: d = 9.824%; • Inexpensive enrichment feasible; • High Q2b = 3034 keV Allowed 2b2n decay to the g.s. of 100Ru observed in several direct experiments, with T1/2 in the range (3.3–11.5) × 1018 yr The most accurate value comes from NEMO-3 (7 kg of 100Mo): T1/2 (2ν; g.s. – g.s.) = (7.1± 0.5) × 1018 yr

6. Double beta decay of 100Mo In addition to the transition to the g.s., the 2b2n decay of 100Mo was registered also for the transition to the first excited 0+1 level of 100Ru T1/2 measured in several experiments: 2b2n decay 100Mo100Ru(0+1) Armonia (meAsuReMent of twO-NeutrIno ββ decAy of 100Mo to the first excited 0+ level of 100Ru ) The aim of the experiment was a remeasurement of 1 kg of Mo enriched in 100Mo to 99.5% used before in the Frejus exp

7. The experimental set-up If the 0+1 excited level of 100Ru (E=1130 keV) is populated, two g quanta with energies of 591 keV and 540 keV will be emitted in cascade in the following deexcitation process Set-up with 4 low-background HPGe detectors (~225 cm3 each one) mounted in one cryostat with a well in the center Set-up enclosed in a lead and copper passive shielding and with a nitrogen ventilation system in order to avoid radon • First data taking (1927 h): sample of metallic 100Mo powder with mass = 1009 g and (99.50.3)% enrichment in 100Mo, but counting rate ~3 times higher than the background rate of the set-up without the sample • Further purification of the sample from radioactive pollutions with procedure based on chemical transformation of metal molybdenum to molybdenum oxide  1199 g of purified 100MoO3 • Effectively removed the pollution of 40K (14 times lower), 137Cs (6 times lower), and U/Th concentration (2 and 4 times lower)

8. Measurements 1-dimensional sum spectrum of all 4 HP Ge detectors Sample of 100MoO3 measured for 18120 h DAQ accumulates both the energy spectra of the individual HP Ge detectors and their coincidences Energy calibration performed before and after the measurements. Internal peaks of known origin (U/Th chains, 40K, 60Co, 137Cs) used to control the energy scale during data taking. The final energy resolution over 3 years of running time is 2.5 keV on the 583 keV line and 4.0 keV on the 1461 keV line background The background of the set-up was collected before and after the measurements with the sample (total time 7711 h) with consistent results;

9. Analysis of the 1-dimensional energy spectrum Both peaks at 540 keV and 591 keV expected for 100Mo→100Ru(01+) 2b2n decay are observed in the data collected with 100MoO3 In the background spectrum they are absent 100MoO3 data N = 4.85  1024 nuclei of 100Mo t = 18120 h e = peaks efficiencies (e540=3.0%; e591=2.9%) a = g conversion coefficient (a540=4.2810-3; a591=3.3210-3) S = number of event in the peaks Background (normalized) • Peak @ 539.5 keV • Fit in [480,560] keV with sum of exponential distribution and two Gaussians: • Peak position = 539.40.2 keV • S540 = 31956 events • c2/dof = 0.76

10. similar results within uncertainties obtained changing exponential to straight line or energy intervals in the fit Analysis of the 1-dimensional energy spectrum • Peak @ 590.8 keV • Fit in [560,625] keV with sum of exponential distribution and four Gaussians: • Peak position = 590.90.2 keV • S540 = 27853 events • c2/dof = 1.4 100MoO3 data Background (normalized) • Systematic uncertainties related with: • the mass of the 100MoO3 sample (0.01%); • the enrichment in 100Mo (0.3%); • the calculation of the live time (0.5%); • the calculation of the efficiencies (10%), estimated comparing calculated and measured efficiencies for a voluminous water source containing several radioactive isotopes in the centre of the 4 HP Ge set-up

11. Analysis of the 2-dimensional energy spectrum Spectrum of the events with multiplicity 2 accumulated in coincidence mode Fixing the energy of one of the detectors to (6095) keV (g line of 214Bi) Example Fixing the energy of one of the detectors to (26155) keV (g line of 208Tl)

12. Analysis of the 2-dimensional energy spectrum Fixing the energy of one of the detectors to the g quanta (591 or 540 keV) emitted in the 2b2n decay 100Mo100Ru(01+), we observe the coincidence peak at the corresponding supplemental energy T = 17807 h Energy of one detector fixed at (5402) keV Energy of one detector fixed at (5912) keV Energy of one detector fixed at (5452) keV (background) Eight events detected (red) Taking into account the efficiency calculated for the coincidence (8.0 × 10−4) we obtain: in agreement with the half life derived in 1-d analysis

13. Possible processes mimicking the 100Mo100Ru(01+) decay • 100Mo + n  101Mo (s=0.199 b; fthermal n @ LNGS= 5.4-11 × 10−7 n cm−2 s−1) • 101Mo (T1/2=14.61 m) b decay 101Tc • g’s from 101Mo b decay:540.1 keV (0.094%) • 590.1 keV (5.6%) • 590.9 keV (16.4%) • + many other g’s • Excluded: • The ratio of the 540 and 591 keV peaks (1:234) is fully different from observed (1:1) • The other g lines from 101Mo decay are absent • Expected only 35–70 captures during 18120 h 10−3 counts in the 540 keV peak 100Mo + p → 100Tc + n (protons produced by fast neutrons or cosmic rays muons) 100Tc (T1/2=15.46 s) b decay 100Ru  the same levels @ 539.5 keV (0.75%) and 1130.3 keV (5.36%) are populated • Excluded: • The contribution from the (p,n) reaction can be ruled out because of low fluxes of fast neutrons (510−8 n cm−2s−1) and cosmic muons (310−8m cm−2s−1) at LNGS and because of the absence of H containing materials close to the 100MoO3 sample

14. Possible processes mimicking the 100Mo100Ru(01+) decay • 100Mo + ne → 100Tc + e-(capture rate of solar ne by 100Mo: 93910−36 atom−1s−1) • 100Tc (T1/2=15.46 s) b decay 100Ru •  as before, levels @ 539.5 keV and 1130.3 keV are populated Excluded: Capture of solar neutrinos would give only 0.3 νe captures in our 100MoO3 sample during 18120 h. 100Mo 2b0n decay to 100Ru(01+)(2b0n g.s.: T1/2 > 1.1 × 1024yr at 90% C.L.) This decay cannot be distinguished observing only emitted deexcitationg Excluded: Supposing equal the nuclear matrix elements for g.s. and 01+ transition and accounting for the different Q2b values (T1/2 Q2b-5) we can expect a number of events 4 orders of magnitude lower than that observed in our measurements.

15. Limit on charge non-conserving b decay of 100Mo by product Search first proposed in [Proc. Nat. Ac. Sci. 45 (1959) 1301] to test the law of conservation of the electric charge. If we suppose that in the b decay: (A,Z)→(A,Z + 1) +e-+ne e- is replaced by some massless particle (e.g. a ne or a g quantum) the energy available in the (A,Z) decay would be increased by 511 keV (the e- rest mass). This would allow transitions to the daughter (A,Z+1) nucleus which are energetically forbidden for the normal b decay.

16. Limit on charge non-conserving b decay of 100Mo by product In the used experimental configuration it is impossible to distinguish the CNC b decay of 100Mo from the 2b process 100Mo→100Ru(01+ ) - tracks of electrons are not registered. h: yield of g quantum in 100Tc b decay (h540= 6.60%; h591= 5.39%) If we consider the observed g quanta as a result of the 2b decay of the 100Mo, we can calculate for Slim: Taking into account only the more conservative value as the final result, we obtain: From the obtained τCNC limit we can derive constraints on the CNC admixture in the weak interactions:

17. Conclusions Data collected at the LNGS with 4 low-background HP Ge detectors for 18120 h with a 1199 g sample of 100MoO3, enriched in 100Mo to 99.5%, allow to observe the 2b2n decay 100Mo→100Ru(01+). The derived half life value is: This value measured is in agreement with the results of previous experiments and does not confirm a previous negative result where a limit of T1/2 > 12× 1020 yr (90% C.L.) was set. Moreover, the measured half life is in reasonable agreement with recent theoretical calculations: 1.8 × 1020 yr (inside the MAVA approach) , (2.6–4.4) × 1020 yr (SSDH), 4.2 × 1020 yr (SSDH), 1.9 × 1020 yr (MCM), 4.5 × 1020 yr (SSDH). The result has been published on Nucl. Phys. A 846 (2010) 143