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

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

3. DAMA/LXe: results on rare processes Dark Matter Investigation Limits on recoils investigating the DMp- 129 Xe elastic scattering by means of PSD Limits on DMp- 129 Xe inelastic scattering Neutron calibration 129 Xe vs 136 Xe by using PSD  SD vs SI signals to increase the sensitivity on the SD component 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 129 Xe during CNC processes N, NN decay into invisible channels in 129 Xe Electron decay: e -  e  2  decay in 136 Xe 2  decay in 134 Xe Improved results on  in 134 Xe, 136 Xe CNC decay 136 Xe  136 Cs N, NN, NNN decay into invisible channels in 136 Xe 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 NIMA482(2002)728 2 decay in 136 Ce and in 142 Ce 2EC2 40 Ca decay 2 decay in 46 Ca and in 40 Ca 2 + decay in 106 Cd 2 and  decay in 48 Ca 2EC2 in 136 Ce, in 138 Ce and  decay in 142 Ce 2 + 0, EC  + 0 decay in 130 Ba Cluster decay in LaCl 3 (Ce) CNC decay 139 La  139 Ce Particle Dark Matter search with CaF 2 (Eu) DAMA/R&D set-up: results on rare processes NPB563(1999)97, Astrop.Phys.7(1997)73 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 RDs on highly radiopure NaI(Tl) set-up; several RDs on low background PMTs; qualification of many materials measurements with a Li 6 Eu(BO 3 ) 3 crystal (NIMA572(2007)734) measurements with 100 Mo sample investigating  decay in the 4π low-bckg HP Ge facility of LNGS (NPA846(2010)143 ) search for 7 Li solar axions (NPA806(2008)388)  decay of 96 Ru and 104 Ru (EPJA42(2009)171) measurements with a Li 2 MoO 4 (NIMA607(2009) 573)  decay of 136 Ce and 138 Ce (NPA824(2009)101) +Many other meas. already scheduled for near future DAMA/Ge & LNGS Ge facility  decay of natural Eu  decay of 113 Cd  decay of 64 Zn, 70 Zn, 180 W, 186 W  decay of 108 Cd and 114 Cd NPA789(2007)15 PRC76(2007)064603 PLB658(2008)193, NPA826(2009)256 EPJA36(2008)167

4. DAMA results on  decay Experimental limits on T 1/2 obtained by DAMA (red) and by previous experiments (blue) all the limits are at 90% C.L. ( except for 2  + 0 in 136 Ce and 2  - 0 in 142 Ce - 68% C.L. ) and in 2010: new observation of 2  decay of 100 Mo to the first excited 0 + level of 100 Ru

5. Double beta decay of 100 Mo 100 Mo: one of the most interesting 2  candidates 1)Natural abundance:  = 9.824%; 2)Inexpensive enrichment feasible; 3)High Q 2  = 3034 keV 2  2 decay is allowed in the Standard Model, it is the most rare nuclear decay ever observed in nature, with T 1/2 in the range of 10 18 –10 24 yr 2  0  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 2  2 decays is also an important tool to test the theoretical models used for the calculations of the nuclear matrix elements for the 2  processes. Allowed 2  2 decay to the g.s. of 100 Ru observed in several direct experiments, with T 1/2 in the range (3.3–11.5) × 10 18 yr The most accurate value comes from NEMO-3 (7 kg of 100 Mo): T 1/2 (2ν; g.s. – g.s.) = (7.1± 0.5) × 10 18 yr

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

7. The experimental set-up Set-up with 4 low-background HPGe detectors (~225 cm 3 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 100 Mo powder with mass = 1009 g and (99.5  0.3)% enrichment in 100 Mo, 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 100 MoO 3 Effectively removed the pollution of 40 K (14 times lower), 137 Cs (6 times lower), and U/Th concentration (2 and 4 times lower) If the 0 + 1 excited level of 100 Ru (E=1130 keV) is populated, two  quanta with energies of 591 keV and 540 keV will be emitted in cascade in the following deexcitation process

8. Measurements The background of the set-up was collected before and after the measurements with the sample (total time 7711 h) with consistent results; Sample of 100 MoO 3 measured for 18120 h 1-dimensional sum spectrum of all 4 HP Ge detectors background 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, 40 K, 60 Co, 137 Cs) 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

9. Analysis of the 1-dimensional energy spectrum Background (normalized) 100 MoO 3 data Both peaks at 540 keV and 591 keV expected for 100 Mo → 100 Ru(0 1 + ) 2  2 decay are observed in the data collected with 100 MoO 3 In the background spectrum they are absent N = 4.85  10 24 nuclei of 100 Mo t = 18120 h  = peaks efficiencies (e 540 =3.0%;  591 =2.9%)  =  conversion coefficient (   =4.28  10 -3 ;  591 =3.32  10 -3 ) S = number of event in the peaks Peak @ 539.5 keV Fit in [480,560] keV with sum of exponential distribution and two Gaussians: Peak position = 539.4  0.2 keV S 540 = 319  56 events  2 /dof = 0.76

10. Peak @ 590.8 keV Fit in [560,625] keV with sum of exponential distribution and four Gaussians: Peak position = 590.9  0.2 keV S 540 = 278  53 events  2 /dof = 1.4 Background (normalized) 100 MoO 3 data Analysis of the 1-dimensional energy spectrum similar results within uncertainties obtained changing exponential to straight line or energy intervals in the fit Systematic uncertainties related with: -the mass of the 100 MoO 3 sample (0.01%); -the enrichment in 100 Mo (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 (  line of 214 Bi) Fixing the energy of one of the detectors to (2615  5) keV (  line of 208 Tl) Example

12. Analysis of the 2-dimensional energy spectrum Taking into account the efficiency calculated for the coincidence (8.0 × 10 −4 ) we obtain: 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) Fixing the energy of one of the detectors to the  quanta (591 or 540 keV) emitted in the 2  2 decay 100 Mo  100 Ru(0 1 + ), we observe the coincidence peak at the corresponding supplemental energy Eight events detected (red) in agreement with the half life derived in 1-d analysis

13. Possible processes mimicking the 100 Mo  100 Ru(0 1 + ) decay A. 100 Mo + n  101 Mo (  =0.199 b;  thermal n @ LNGS = 5.4-11 × 10 −7 n cm −2 s −1 ) 101 Mo ( T 1/2 =14.61 m )  decay  101 Tc   ’s from 101 Mo  decay: 540.1 keV (0.094%) 590.1 keV (5.6%) 590.9 keV (16.4%) + many other  ’s Excluded: (a)The ratio of the 540 and 591 keV peaks (1:234) is fully different from observed (1:1) (b)The other  lines from 101 Mo decay are absent (c)Expected only 35–70 captures during 18120 h  10 −3 counts in the 540 keV peak B. 100 Mo + p → 100 Tc + n (protons produced by fast neutrons or cosmic rays muons) 100 Tc ( T 1/2 =15.46 s )  decay  100 Ru  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 −2 s −1 ) and cosmic muons (3  10 −8  cm −2 s −1 ) at LNGS and because of the absence of H containing materials close to the 100 MoO 3 sample

14. Possible processes mimicking the 100 Mo  100 Ru(0 1 + ) decay C. 100 Mo + e → 100 Tc + e - (capture rate of solar e by 100 Mo: 939  10 −36 atom −1 s −1 ) 100 Tc ( T 1/2 =15.46 s )  decay  100 Ru  as before, levels @ 539.5 keV and 1130.3 keV are populated Excluded: Capture of solar neutrinos would give only 0.3 ν e captures in our 100 MoO 3 sample during 18120 h. D. 100 Mo 2  0 decay to 100 Ru(0 1 + ) (2  0  g.s.: T 1/2 > 1.1 × 10 24 yr at 90% C.L.) This decay cannot be distinguished observing only emitted deexcitation  Excluded: Supposing equal the nuclear matrix elements for g.s. and 0 1 + transition and accounting for the different Q 2  values (T 1/2  Q 2   ) we can expect a number of events 4 orders of magnitude lower than that observed in our measurements.

15. 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  decay: (A,Z) → (A,Z + 1) +e - + e e - is replaced by some massless particle (e.g. a e or a  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  decay. by product Limit on charge non-conserving  decay of 100 Mo

16. In the used experimental configuration it is impossible to distinguish the CNC  decay of 100 Mo from the 2  process 100 Mo → 100 Ru(0 1 + ) - tracks of electrons are not registered. If we consider the observed  quanta as a result of the 2  decay of the 100 Mo, we can calculate for S lim :  : yield of  quantum in 100 Tc  decay (  540 = 6.60%;  591 = 5.39%) Taking into account only the more conservative value as the final result, we obtain: From the obtained τ CNC limit we can derive constraints on the CNC admixture in the weak interactions: by product

17. Conclusions Data collected at the LNGS with 4 low-background HP Ge detectors for 18120 h with a 1199 g sample of 100 MoO 3, enriched in 100 Mo to 99.5%, allow to observe the 2  2 decay 100 Mo → 100 Ru(0 1 + ). 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 T 1/2 > 12× 10 20 yr (90% C.L.) was set. Moreover, the measured half life is in reasonable agreement with recent theoretical calculations: 1.8 × 10 20 yr (inside the MAVA approach), (2.6–4.4) × 10 20 yr (SSDH), 4.2 × 10 20 yr (SSDH), 1.9 × 10 20 yr (MCM), 4.5 × 10 20 yr (SSDH). The result has been published on Nucl. Phys. A 846 (2010) 143