Investigations on Dark Matter and ββ decays by DAMA at Gran Sasso

Transcription

1 Investigations on Dark Matter and ββ decays by DAMA at Gran Sasso NDB07 - NEUTRINOLESS DOUBLE BETA Ahmedabad (India) February 5, 2007 R. Bernabei Università di Roma Tor Vergata INFN-Roma Tor Vergata

2 Roma2,Roma1,LNGS,IHEP/Beijing (+ in some small scale expts and by-products results: INR-Kiev + in the framework of MAE activ. for studies on double positron decays: IIT - Kharagpur + neutron measurements: ENEA- Frascati) DAMA/NaI DAMA/LIBRA DAMA/LXe DAMA/R&D low bckg DAMA/Ge for sampling meas. meas. with 100 Mo

3 The annual modulation: a model independent signature for the investigation of Dark Matter particles component in the galactic halo With the present technology, the annual modulation is the main model independent signature for the DM signal. Although the modulation effect is expected to be relatively small a suitable large-mass, low-radioactive set-up with an efficient control of the running conditions would point out its presence. Drukier, Freese, Spergel PRD86 Freese et al. PRD88 30 km/s December v sun ~ 232 km/s (Sun velocity in the halo) v orb = 30 km/s (Earth velocity around the Sun) γ = π/3 ω = 2π/T T = 1 year t 0 = 2 nd June (when v is maximum) June 30 km/s ~ 232 km/s 60 Requirements of the annual modulation S k v (t) = v sun + v orb cosγcos[ω(t-t 0 )] dr [ η( t)] = der S0, k + Sm, k cos[ ω( t t0)] de E k R Expected rate in given energy bin changes because the annual motion of the Earth around the Sun moving in the Galaxy 1) Modulated rate according cosine 2) In a definite low energy range 3) With a proper period (1 year) 4) With proper phase (about 2 June) 5) For single hit events in a multi-detector set-up 6) With modulation amplitude in the region of maximal sensitivity must be <7% for usually adopted halo distributions, but it can be larger in case of some possible scenarios To mimic this signature, spurious effects and side reactions must not only - obviously - be able to account for the whole observed modulation amplitude, but also to satisfy contemporaneously all the requirements

4 Competitiveness of NaI(Tl Tl) ) set-up High duty cycle Well known technology Large mass possible Ecological clean set-up; no safety problems Cheaper than every other considered technique Small underground space needed High radiopurity by selections, chem./phys. purifications, protocols reachable Well controlled operational condition feasible Routine calibrations feasible down to kev range in the same conditions as the production runs Neither re-purification procedures nor cooling down/warming up (reproducibility, stability,...) Absence of microphonic noise + effective noise rejection at threshold (τ of NaI(Tl) pulses hundreds ns, while τ of noise pulses tens ns) High light response ( ph.e./kev) Sensitive to SI, SD, SI&SD couplings and to other existing scenarios, on the contrary of many other proposed target-nuclei Sensitive to both high (by Iodine target) and low mass (by Na target) candidates Effective investigation of the annual modulation signature feasible in all the needed aspects PSD feasible at reasonable level etc. A low background NaI(Tl) also allows the study of several other rare processes such as: possible processes violating the Pauli exclusion principle, CNC processes in 23 Na and 127 I, electron stability, nucleon and dinucleon decay into invisible channels, neutral SIMP and nuclearites search, solar axion search,... High benefits/cost

5 Highly radiopure DAMA/NaI NaI(Tl)~100 kg Performances: N.Cim.A112(1999) , EPJC18(2000)283, Riv.N.Cim.26 n. 1(2003)1-73, IJMPD13(2004)2127 Results on rare processes: Possible Pauli exclusion principle violation CNC processes Electron stability and non-paulian transitions in Iodine atoms (by L-shell) Search for solar axions Exotic Matter search Search for superdense nuclear matter Search for heavy clusters decays PLB408(1997)439 PRC60(1999) PLB460(1999)235 PLB515(2001)6 EPJdirect C14(2002)1 EPJA23(2005)7 EPJA24(2005)51 Results on DM particles: PSD PLB389(1996)757 Investigation on diurnal effect N.Cim.A112(1999)1541 Exotic Dark Matter search PRL83(1999)4918 Annual Modulation Signature PLB424(1998)195, PLB450(1999)448, PRD61(1999)023512, PLB480(2000)23,EPJ C18(2000)283, PLB509(2001)197, EPJ C23 (2002)61, PRD66(2002)043503, Riv.N.Cim.26 n.1 (2003)1-73, IJMPD13(2004)2127, IJMPA21(2006)1445), EPJC47(2006)263 + other works in progress... total exposure collected in 7 annual cycles data taking completed on July 2002 (still producing results) kg d

6 Reduced standard contaminants (e.g. U/Th of order of ppt) by material selection and growth/handling protocols. PMTs:Each crystal coupled - through 10cm long tetrasil-b light guides acting as optical windows - to 2 low background EMI9265B53/FL (special development) 3 diameter PMTs working in coincidence. Detectors inside a sealed Cu box maintained in HP Nitrogen atmosphere in slight overpressure Very low radioactive shields: 10 cm of highly radiopure Cu, 15 cm of highly radiopure Pb + shield from neutrons: Cd foils + polyethylene/paraffin+ ~ 1 m concrete moderator largely surrounding the set-up Installation sealed: A plexiglas box encloses the whole shield and is also maintained in HP Nitrogen atmosphere in slight overpressure. Walls, floor, etc. of inner installation sealed by Supronyl ( cm 2 /s permeability).three levels of sealing from environmental air. Installation in air conditioning + huge heat capacity of shield Calibration using the upper glove-box (equipped with compensation chamber) in HP Nitrogen atmosphere in slight overpressure calibration in the same running conditions as the production runs. Energy and threshold: Each PMT works at single photoelectron level. Energy threshold: 2 kev (from X-ray and Compton electron calibrations in the kev range and from the features of the noise rejection and efficiencies). Data collected from low energy up to MeV region, despite the hardware optimization was done for the low energy Pulse shape recorded over 3250 ns by Transient Digitizers. Monitoring and alarm system continuously operating by self-controlled computer processes. + electronics and DAQ fully renewed in summer 2000 Il Nuovo Cim. A112 (1999) , EPJC18(2000)283, Riv. N. Cim. 26 n.1 (2003)1-73, IJMPD13(2004)2127 Main procedures of the DAMA data taking for the DMp annual modulation signature data taking of each annual cycle starts from autumn/winter (when cosω(t-t 0 ) 0) toward summer (maximum expected). routine calibrations for energy scale determination, for acceptance windows efficiencies by means of radioactive sources each ~ 10 days collecting typically ~10 5 evts/kev/detector + intrinsic calibration from 210 Pb (~ 7 days periods) + periodical Compton calibrations, etc. continuous on-line monitoring of all the running parameters with automatic alarm to operator if any out of allowed range.

7 The model independent result Annual modulation of the rate: DAMA/NaI 7 annual cycles experimental single-hit residuals rate vs time and energy Riv. N. Cim. 26 n.1. (2003) 1-73, IJMPD13(2004) kg d Acos[ω(t-t 2-4 kev 0 )] ; continuous lines: t 0 = d, T = 1.00 y 2-5 kev fit: A=( ± ) cpd/kg/kev 2-6 kev Time (day) fit: A = ( ± ) cpd/kg/kev Time (day) Absence of modulation? No χ 2 /dof=71/37 P(A=0)= fit: A = ( ± ) cpd/kg/kev Time (day) fit (all parameters free): A = ( ± ) cpd/kg/kev; t 0 = (140 ± 22) d ; T = (1.00 ± 0.01) y The data favor the presence of of a modulated behavior with proper features at at 6.3σ C.L.

8 Low energy vs higher energy Single-hit residual rate as in a single annual cycle 10 5 kg day Power spectrum of single-hit residuals Treatment of the experimental errors and time binning included here 6.3 σ C.L. fixing t 0 = day and T = 1.00 y, the modulation amplitude: A=( ± ) cpd/kg/kev A= -( ± ) cpd/kg/kev 2-6 kev 6-14 kev Clear modulation present in the lowest energy region: from the energy threshold, 2 kev, to 6 kev. No modulation found: in the 6-14 kev energy regions in other energy regions closer to that where the effect is observed e.g.: mod. ampl. (6-10 kev): -( ±0.0065), (0.0012±0.0059) and (0.0035±0.0058) cpd/kg/kev for DAMA/NaI-5,DAMA/NaI-6 and DAMA/NaI-7; statistically consistent with zero Principal mode in the 2-6 kev region d -1 1 y -1 Not present in the 6-14 kev region (only aliasing peaks) in the integral rate above 90 kev, e.g.: mod. ampl.: (0.09±0.32), (0.06±0.33) and - (0.03±0.32) cpd/kg for DAMA/NaI-5, DAMA/NaI-6 and DAMA/NaI-7; statistically consistent with zero + if a modulation present in the whole energy spectrum at the level found in the lowest energy region R 90 tens cpd/kg 100 σ far away

9 Multiple-hits events in the region of the signal In DAMA/NaI-6 and 7 each detector has its own TD (multiplexer system removed) pulse profiles of multiple-hits events (multiplicity > 1) also acquired (total exposure: kg d). The same hardware and software procedures as the ones followed for single-hit events just one difference: events induced by Dark Matter particles do not belong to this class of events, that is: multiple-hits events = Dark Matter particles events switched off 2-6 kev residuals Residuals for multiple-hits events (DAMA/NaI-6 and 7) Mod ampl. = -(3.9±7.9) 10-4 cpd/kg/kev Residuals for single-hit events (DAMA/NaI 7 annual cycles) Mod ampl. = (0.0195±0.0031) cpd/kg/kev This result offers an additional strong support for the presence of Dark Matter particles in the galactic halo further excluding any side effect either from hardware or from software procedures or from background

10 Running conditions Temperature Nitrogen Flux an example: DAMA/NaI-6 hardware rate Distribution of some parameters Radon outside the shield Pressure Running conditions stable at level < 1% Modulation amplitudes obtained by fitting the time behaviours of main running parameters, acquired with the production data, when including a modulation term as in the Dark Matter particles case. outside the shield All the measured amplitudes well compatible with zero + none can account for the observed effect (to mimic such signature, spurious effects and side reactions must not only be able to account for the whole observed modulation amplitude, but also simultaneously satisfy all the 6 requirements) [for details and for the other annual cycles see for example: PLB424(1998)195, PLB450(1999)448, PLB480(2000)23, RNC26(2003)1-73, EPJC18(2000)283, IJMPD13(2004)2127]

11 Summary of the results obtained in the investigations of possible systematics or side reactions (see Riv. N. Cim. 26 n. 1 (2003) 1-73, IJMPD13(2004)2127 and references therein) Source Main comment Cautious upper limit (90%C.L.) RADON Sealed Cu box in HP Nitrogen atmosphere,etc <0.2% S obs m TEMPERATURE Installation is air conditioned+ <0.5% S obs m detectors in Cu housings directly in contact with multi-ton shield huge heat capacity + T continuously recorded NOISE Effective noise rejection <1% S obs m ENERGY SCALE Periodical calibrations + continuous monitoring <1% S obs m of 210 Pb peak EFFICIENCIES Regularly measured by dedicated calibrations <1% S obs m BACKGROUND No modulation observed above 6 kev + this limit <0.5% S obs m includes possible effect of thermal and fast neutrons + no modulation observed in the multiple-hits events in 2-6 kev region SIDE REACTIONS Muon flux variation measured by MACRO <0.3% S obs m + even if larger they cannot satisfy all the requirements of annual modulation signature Thus, they can not mimic the observed annual modulation effect

12 Summary of the DAMA/NaI Model Independent result Presence of modulation over 7 annual cycles at ~6.3σ C.L. with the proper distinctive features of the signature; all the features satisfied by the data over 7 independent experiments of 1 year each one Absence of known sources of possible systematics and side processes able to quantitatively account for the observed effect and to contemporaneously satisfy the many peculiarities of the signature No other experiment whose result can be directly compared in model independent way is available so far To investigate the nature and coupling with ordinary matter of the possible DM candidate(s), effective energy and time correlation analysis of the events has to be performed within given model frameworks Corollary quests for candidate(s) astrophysical models: ρ DM, velocity distribution and its parameters nuclear and particle Physics models + experimental parameters e.g. for WIMP class particles: SI, SD, mixed SI&SD, preferred inelastic, scaling laws on cross sections, form factors and related parameters, spin factors, halo models, etc. + other candidates + different scenarios + multicomponent? THUS uncertainties on models and comparisons

13 Few examples of corollary quests for the WIMP class in given scenarios (Riv. N.Cim. vol.26 n.1. (2003) 1-73, IJMPD13(2004)2127) DM particle with elastic SI&SD interactions (Na and I are fully sensitive to SD interaction, on the contrary of e.g. Ge and Si) Examples of slices of the allowed volume in the space (ξσ SI, ξσ SD, m W, θ) for some of the possible θ (tgθ =a n /a p with 0 θ<π) and m W not exhaustive + different scenarios? DM particle with dominant SI coupling Region of interest for a neutralino in supersymmetric schemes where assumption on gaugino-mass unification at GUT is released and for generic DM particle Already most of these allowed volumes/regions are unexplorable e.g. by Ge, Si,TeO 2, Ar, Xe, CaWO 4 targets Model dependent lower bound on neutralino mass as derived from LEP data in supersymmetric schemes based on GUT assumptions (DPP2003) higher mass region allowed for low v 0, every set of parameters values and the halo models: Evans logarithmic C1 and C2 co-rotating, triaxial D2 and D4 non-rotating, Evans power-law B3 in seta DM particle with dominant SD coupling volume allowed in the space (m W, ξσ SD,θ); here example of a slice for θ=π/4 (0 θ<π) DM particle with preferred inelastic interaction: W + N W* + N (S m /S 0 enhanced): examples of slices of the allowed volume in the space (ξσ p, m W,δ) [e.g. Ge disfavoured] Regions above 200 GeV allowed for low v 0, for every set of parameters values and for Evans logarithmic C2 corotating halo models

14 Supersymmetric expectations in MSSM Assuming for the neutralino a dominant purely SI coupling when releasing the gaugino mass unification at GUT scale: M 1 /M (<); (where M 1 and M 2 U(1) and SU(2) gaugino masses) low mass configurations are obtained figure taken from PRD69(2004) scatter plot of theoretical configurations vs DAMA/NaI allowed region in the given model frameworks for the total DAMA/NaI exposure (area inside the green line); (for previous DAMA/NaI partial exposure see PRD68(2003)043506)

15 ... investigating halo substructures by underground expt through annual modulation Possible contributions due to the tidal stream of Sagittarius Dwarf satellite (SagDEG) galaxy of Milky Way EPJC47(2006)263 spherical oblate simulations from Ap.J.619(2005)807 stream sun Examples of the effect of SagDEG tail on the phase of the signal annual modulation V 8* V sph V obl V 8* from 8 local stars: PRD71(2005)043516

16 Investigating the effect of SagDEG contribution for WIMPs in given scenarios DAMA/NaI: seven annual cycles kg d for different SagDEG velocity dispersions ( km/s) ρ SagDEG < 0.1 GeV cm -3 (bound by M/L ratio considerations) mixed SI&SD case green area: no SagDEG pure SI case EPJC47(2006)263 pure SD case

17 other astrophysical scenarios? Possible other (beyond SagDEG) non-thermalized component in the galactic halo? In the galactic halo, fluxes of Dark Matter particles with dispersion velocity relatively low are expected : Possible presence of caustic rings streams of Dark Matter particles P. Sikivie, Fu-Sin Ling et al. astro-ph/ Interesting scenarios for DAMA Effect on S m /S o respect to usually adopted halo models? Effect on the phase of annual modulation signature? Canis Major simulation: astro-ph/ Other dark matter stream from satellite galaxy of Milky Way close to the Sun? Position of the Sun:...very likely... (-8,0,0) kpc Can be guess that spiral galaxy like Milky Way have been formed capturing close satellite galaxy as Sgr, Canis Major, ecc

18 Another class of DM candidates: light bosonic particles The detection is based on the total conversion of the absorbed mass into electromagnetic radiation. IJMPA21(2006)1445 In these processes the target nuclear recoil is negligible and not involved in the detection process (i.e. signals from these candidates are lost in experiments applying rejection procedures of the electromagnetic contribution, as CDMS, Edelweiss,CRESST, WARP, Xenon, ) Axion-like particles: similar phenomenology with ordinary matter as the axion, but significantly different values for mass and coupling constants allowed. A wide literature is available and various candidate particles have been and can be considered. A complete data analysis of the total kgxday exposure from DAMA/NaI has been performed for pseudoscalar (a) and scalar (h) candidates in some of the possible scenarios. They can account for the DAMA/NaI observed effect as well as candidates belonging to the WIMPs class Main processes involved in the detection:,h,h h a S 0 S 0,S m S 0,S m h S 0,S m S 0 S 0,S m

19 Pseudoscalar case: Analysis of kg day exposure from DAMA/NaI. DAMA/NaI allowed region in the considered framework. All these configurations are allowed by DAMA/NaI depending on the relative contributions of charged fermion couplings IJMPA21(2006)1445 Considered dark halo models as in refs.: Riv.N.Cim. 26 n.1. (2003) 1-73 IJMPD 13 (2004) 2127 Maximum allowed photon coupling coupling model g auu and g add region almost indipendent on other fermion coupling values. Only electron coupling τ a =15Gy Also this can account for the DAMA/NaI observed effect g aγγ coupling to photons vanish at first order: α g π m aee e g m add d g m auu u 0 majoron as in PLB 99 (1981) 411 g m aee e g add gauu = = τ 3 md mu UHECR [3] PRD64(2001) h

20 Analysis of kg day exposure from DAMA/NaI. DAMA/NaI allowed region in the considered framework. Scalar case: Considered dark halo models as in ref: Riv.N.Cim. 26 n.1. (2003) 1-73 IJMPD 13 (2004) 2127 Just an example: all the couplings to quarks of the same order lifetime dominated by u & d loops: g hγγ 2 2 α Qq g 3 π m q q hqq 2 α π 4 9 g m huu u g m hdd d g hnn Z ( g + g ) + ( g g ) = 2 huu hdd huu hdd Annual modulation signature present for a scalar particle with pure coupling to hadronic matter (possible gluon coupling at tree level?). Compton-like to nucleus conversion is the dominant process for particle with cosmological lifetime. A Also this can account for the DAMA/NaI observed effect Many other configurations of cosmological interest are possible depending on the values of the couplings to other quarks and to gluons. Allowed by DAMA/NaI (for m h > 0.3 kev ) τ h > 15 Gy (lifetime of cosmological interest) m u = 3.0 ± 1.5 MeV m d = 6.0 ± 2.0 MeV h

21 FAQ:... DAMA/NaI excluded by others? OBVIOUSLY NO They give a single model dependent result using other target DAMA/NaI gives a model independent result using 23 Na and 127 I targets No direct model independent comparison possible Even assuming their expt. results as they give them Case of DM particle scatterings on target-nuclei In general? OBVIOUSLY NO The results are fully decoupled either because of the different sensitivities to the various kinds of candidates, interactions and particle mass, or simply taking into account the large uncertainties in the astrophysical (realistic and consistent halo models, presence of nonthermalized components, particle velocity distribution, particle density in the halo,...), nuclear (scaling laws, FFs, SF) and particle physics assumptions and in all the instrumental quantities (quenching factors, energy resolution, efficiency,...) and theor. parameters. At least in the purely SI coupling they only consider? OBVIOUSLY NO still room for compatibility either at low DM particle mass or simply accounting for the large uncertainties in the astrophysical, nuclear and particle physics assumptions and in all the expt. and theor. parameters. Case of bosonic candidate (full conversion into electromagnetic radiation) These candidates are lost by these expts. OBVIOUSLY NO.and more (they usually quote in an uncorrect, partial and unupdated way the implications of the DAMA/NaI model independent result; they release orders of magnitude lower exposures,

22 What about the indirect searches of DM particles in the space? EGRET data shows an excess of gamma ray fluxes for energies above 1 GeV in the galactic disk and for all sky directions. The EGRET Excess of Diffuse Galactic Gamma Rays astro-ph/ PLB536(2002)263 EGRET data, W.de Boer, hep-ph/ interpretation, evidence itself, derived m W and cross sections depend e.g. on bckg modeling, on DM spatial velocity distribution in the galactic halo, etc. Hints from indirect searches are not in conflict with DAMA/NaI for the WIMP class candidate In next years new data from DAMA/LIBRA (direct detection) and from Agile, Glast, Ams2, Pamela,... (indirect detections)

23 A platform where to sleep What is an iceberg? A fishing preserve A dangerous place

24 The The new newdama/libra set-up ~250 ~250 kg kg NaI(Tl) (Large sodium Iodide Bulk Bulk for forrare RAreprocesses) As a result of a second generation R&D for more radiopure NaI(Tl) by exploiting new chemical/physical radiopurification techniques (all operations involving crystals and PMTs - including photos - in HP Nitrogen atmosphere) PMT +HV divider Cu etching with super- and ultrapure HCl solutions, dried and sealed in etching staff at work in clean room HP N 2 storing new crystals improving installation and environment

25 (all operations involving crystals and PMTs -including photos- in HP N 2 atmosphere) closing the Cu box housing the detectors view at end of detectors installation in the Cu box detectors during installation; in DAMA/LIBRA in data taking since March 2003, the central and right up detectors the new shaped Cu e.g. up to March 2006: installing DAMA/LIBRA detectors shield surrounding light guides Collected exposure: of order of 10 (acting 5 kg also x d as optical windows) assembling a DAMA/ LIBRA sources detector data: of order of 4 x 10 7 events and PMTs was not yet applied filling the inner Cu box Regularly with continuing the data taking further shield 1st data release not later than end 2008

26 Summary on Dark Matter investigation DAMA/NaI data show a 6.3σ C.L. model independent evidence for the presence of a Dark Matter particle component in the galactic halo Corollary model dependent quest for the candidate particle: WIMP particles with m w ~ (few GeV to TeV) with coupling pure SI or pure SD or mixed SI/SD as well as particles with preferred inelastic scattering (Riv.N.Cim. 26 n.1. (2003) 1-73, IJMPD 13 (2004) 2127) several other particles suggested in literature by various authors (see literature) bosonic particles with m a ~ kev having pseudoscalar, scalar coupling (IJMPA21(2006)1445) halo substructures (SagDEG) effects (EPJC47(2006)263) and more in progress on halo models, candidates, type of interactions... The presently running DAMA/LIBRA will allow to further increase the C.L. of the model independent result, and will allow to restrict the nature of the candidate and to investigate the phase space structure of the dark halo + a new R&D towards a possible ton set-up we proposed in 1996 in progress... wait for more in the near future + many other measurements in progress with the other set-ups

27 DAMA investigations on ββ decays at Gran Sasso

28 DAMA/LXe 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 NIMA482(2002)728 DAMA/R&D 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: 2β decay in 136 Xe 2β decay in 134 Xe e - ν e γ Improved results on 2β in 134 Xe, 136 Xe CNC decay 136 Xe 136 Cs N, NN, NNN decay into invisible channels in 136 Xe R&D set-up: results on rare processes Particle Dark Matter search with CaF 2 (Eu) Astrop.Phys5(1996)217 PLB465(1999)315 PLB493(2000)12 PRD61(2000) Xenon01 PLB527(2002)182 PLB546(2002)23 Beyond the Desert (2003) 365 EPJA27 s01 (2006) 35 NPB563(1999)97, Astrop.Phys.7(1997)73 2β decay in 136 Ce and in 142 Ce 2EC2ν 40 Ca decay 2β decay in 46 Ca and in 40 Ca 2β + decay in 106 Cd 2β and β decay in 48 Ca 2EC2ν in 136 Ce, in 138 Ce and α decay in 142 Ce 2β + 0ν and EC β + 0ν decay in 130 Ba Cluster decay in LaCl 3 (Ce) CNC decay 139 La 139 Ce Il Nuov.Cim.A110(1997)189 Astrop. Phys. 7(1999)73 NPB563(1999)97 Astrop.Phys.10(1999)115 NPA705(2002)29 NIMA498(2003)352 NIMA525(2004)535 NIMA555(2005)270 UJP51(2006)1037

29 Advantages of scintillators for ββ decay Mainly active source technique (but also passive source technique is possible with relatively high efficiency) Low cost Large masses possible Well known technology Suitable energy resolution in most cases Several isotope candidates Experienced: Several low background experiments already carried out Developments to improve the low background features possible Exploiting coincidences and anticoincidences techniques Fragmented set-ups PSD often feasible High duty cycle Schematic view of the set-up for Cd experiment PMT Light guide NaI(Tl) C d NaI(Tl) Light guide PMT DAMA & ββ decays searches for ββ (β β, β + β +, ECβ +, 2EC) decay modes by active source technique (exploiting - in some cases - coincidence/anticoincidence technique) in: 40 Ca; 46 Ca; 48 Ca; 130 Ba; 136 Ce; 138 Ce; 142 Ce; 134 Xe; 136 Xe; and by the passive source technique using low backg NaI(Tl) ) : 106 Cd Schematic view of the set-up for Ba experiment γ γ e + e + γ γ

30 DAMA results on ββ 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 2β + 0ν in 136 Ce and 2β - 0ν in 142 Ce - 68% C.L.) Now in progress measurement on 2β2ν decay in 100 Mo to the first excited level of 100 Ru by using ~1 kg of Molybdenum enriched in 100 Mo at 99.5% inserted in a 4 HP Ge detector array

31 2β +, β + /EC and EC/EC processes in 106 Cd - I Astrop.Phys.10(1999)115 The β + EC and 2β + decay of 106 Cd can be identified by searching for simultaneous emission of 2 or 4 γ of 511 kev The γ s will be detected in coincidence by two low background NaI(Tl) scintillators placed around the Cd sample Cadmium NaI-1 γ γ e + e + γ NaI-2 γ Cadmium sample (a mm 2 plate), 109 g double purification + 45 g single purification: 154 g enriched in 106 Cd at 68% Detectors: two low background NaI(Tl) (4 4 4 ) Running time: 4321 h. Events recorded in case of coincidence between the NaI(Tl) 106 Cd 106 Pd (δ=1.25%; M A =2771 kev); Resolution of the two NaI(Tl) measured by using γ sources: FWHM(E) = ( E) 1/2 FWHM(E) = ( E) 1/2 (E in kev) In DAMA/R&D Two-dimensional coincidence spectra of NaI(Tl) detectors (a) experimental spectrum measured with enriched 106 Cd during 1489 h; (b) 22 Na calibration spectrum; (c) model spectrum of the 232 Th decay chain in the 106 Cd sample; (d) model spectrum of the 2β + decay of 106 Cd.

32 Radioactive contaminations of Cd samples and PMTs - II Background spectrum of NaI-2 when E NaI-1 > 400keV (T=2851 h) Cadmium Astrop.Phys.10(1999)115 NaI-1 NaI Ra Simulated spectra considering Th 232 Th and Ra radioactive contamination of the 106 Cd samples E NaI-2 (kev) Considering the achieved radiopurity in the developments of highly radiopure NaI(Tl) crystals, to estimate the locations and quantities of the main radioactive residual pollution in the setup, we put our attention on the contamination of the cadmium samples and PMTs: Cadmium: 232 Th = (0.13±0.01) mbq/g 226 Ra = (0.12±0.04) mbq/g 40 K < 2mBq/g PMTs: 232 Th = (1.8±0.6) mbq/g 226 Ra < 1.3 mbq/g 40 K < 6mBq/g

33 4321 h 2β +, β + /EC and EC/EC processes in E NaI-1 =511±30 kev E NaI-2 (kev) 226 Ra Simulated spectra considering 232 Th Th and Ra radioactive contamination of the 106 Cd samples residual spectrum New improved limits on T 1/2 for 2β +, β + /EC and EC/EC decay channels Limits are in the range (0.3-4) y at 90% C.L. in 106 Decay mode (transition) β + /EC (2ν) g.s. g.s. β + /EC(0ν+0νM) g.s. g.s. β + (0ν+2ν+0νM) g.s (1134 kev) β + (0ν+2ν+0νM) g.s (512 kev) β + (0ν+2ν+0νM) g.s (1128 kev) 2β + (0ν+2ν+0νM) g.s. g.s. 2β + (0ν+2ν+0νM) g.s (512 kev) EC/EC (0ν) g.s. 1,2 + (2741 kev) EC/EC (2ν+0νM ) g.s (1134 kev) EC/EC (2ν+0νM ) g.s (1128 kev) Limits significantly higher (factor 6 to 60) than those previously published Cd Cd Peak efficiency (E 1 - E 2 ) kev 9.3% ( ) 8.4% ( ) 2.8% ( ) 5.7% ( ) 3.2% ( ) 5.5% ( ) 3.6% ( ) 0.71% ( ) 1.6% ( ) 1.03% ( ) III Astrop.Phys.10(1999)115 Obtained experimental limits T 1/2 limits (90% C.L.) y y y y y y y y y y Further efforts in progress

34 Performances of a CeF 3 crystal scintillator and its application to the search for rare processes - I NIMA498(2003)352 Detector: CeF 3 scintillator (2x2x2 cm 3, mass 49.3 g) directly coupled to 2 low background PMTs working in coincidence in DAMA/R&D Investigations: 1) α/β light ratio α/β = E α (kev) 2) PSD Population of α slightly shifted respect to γ(β) 3) BiPo events 4) Radioactive contaminations Background spectrum: 2142 h 5) 2ν2EC decay of 136 Ce and 138 Ce and α decay of 142 Ce 136 Ce 136 Ba 138 Ce 138 Ba 142 Ce 138 Ba (δ=0.19%; M A =2400 kev); (δ=0.25%; M A =693 kev); (δ=11.1%; E α =1263 kev);

35 Performances of the CeF 3 crystal scintillator - II 1) α/β light ratio NIMA498(2003)352 Measured with a collimated 241 Am α source using different thin absorbers of known thickness to vary the energy of α beam + α peaks of 220 Rn, 216 Po and 212 Po from thorium contamination; α energy range MeV; α/β = E α (kev) 2) PSD γ MeV (with 137 Cs and 60 Co sources) α MeV (using α active impurities inside the crystal) Population of α events slightly shifted respect to the γ(β) population

36 In the inset: the energy spectra selected by PSD as γ(β) events (solid line) and α events (points) are shown. 3) BiPo events Performances of the CeF 3 crystal scintillator - III 4) Radioactive contaminations Background spectrum measured during 2142 h The result of fit (solid line) and the most important background components (internal contamination by 232 Th daughter nuclides and external γ radiation from the 2 PMTs) are presented. NIMA498(2003)352 The energy (a,b) and time (c) distributions of the fast sequence of β ( 212 Bi; Q β = 2254 kev) and α ( 212 Po; E α = 8784 kev; T 1/2 = 0.299(2) µs decays selected by PSD from the background data recorded over 2142 h. (d) Time profile of a BiPo event The fit on the time distribution (c) gives T 1/2 = 0.289(8) µs in good agreement with the value reported in literature (From time-amplitude analysis also first and second α s from 220 Rn -> 216 Po -> 212 Pb identified)

37 RESULTS - IV NIMA498(2003)352 Limits at 90% C.L. (68% C.L.): 136 Ce 2ν2K: T 1/2 > 2.7(4.5) y 138 Ce 2ν2K: T 1/2 > 3.7(6.1) y 142 Ce α: T 1/2 > 2.9(7.3) y Difficulties: In the purification and growth; relatively small crystal size. Ce samples. Tested detectors along the time from Preciosa-Crytur, from Chinese companies and from Crystal Clear Coll. Perspectives: Developping material selection, purification procedures and growing/handling protocol to achieve the main reduction of U/Th ( 14ppb 232 Th and 238 U 6 ppb, nat K 10 ppm in commercial detectors)

38 Example of perspectives R&D s to identify the best experimental set-up - for radiopurity, technical complexity and cost - to exploit the distinctive signatures arising from β + β + /ECβ + /2EC decay modes γ γ e + e + γ γ Main isotopes which are planned to be investigated (further) in next future with new measurements/r&d s: active source technique: R&D s on further radiopure scintillators containing: 136 Ce(β + β + /ECβ + /2EC), 130 Ba(β + β + /ECβ + /2EC), 40 Ca(2EC), 106 Cd (β + β + /ECβ + /2EC) Liquid/gaseous detectors (as DAMA/LXe set-up) filled with liquid/gas containing: 124 Xe (β + β + /ECβ + /2EC), 78 Kr (β + β + /ECβ + /2EC), 36 Ar(2EC) Trigger: almost zero background expected in highly radiopure set-ups T 1/2 MT instead of (but sometimes larger expected half-life) MT tests by the passive source technique using highly radiopure NaI(Tl) with: 58 Ni(EC β + /2EC), 96 Ru (β + β + /ECβ + /2EC) ( M A = 1.9 MeV, 2.7 MeV, respectively) Choice of large mass set-ups connected with the possibilities arising from R&D/tests

39 Summary of the results on ββ and perspectives DAMA has investigated aand is investigating several ββ (β - β -, β + β +, ECβ +, 2EC) decay modes for differents isotopes by exploiting the passive and the active source technique developing and using low background scintillators and achieving several interesting/competing results β β versus β + β + /ECβ + /2EC decays modes The β + β + /ECβ + decay modes investigations can offer a better possibility to separate the signal from the background, because of the associated positron annihilation gamma s s and give complementary information For some isotopes and decay mode expected half-life life comparable or even lower than in some β - β - cases DAMA will continue efforts toward higher radiopure detectors for both cases and continue the lines on Xe,, Cd, Ce,Ba + at present in 1kg of enriched 100Mo and a ZnWO detector... Joint efforts towards more deep (experimental and theoretical) investigations of the β + β + /ECβ + /2EC decay modes are quite remarkable

40 Conclusions DAMA has realized many searches for rare processes by developing and using low radioactive scintillators Several competing results have been achieved Many other works are in progress, in particular on Dark Matter (DAMA/LIBRA and RD towards a possible DAMA/1ton) and ββ processes (new scintillators under either in measurement or in development or in considerations)