Sensitivity, performance, stability and intrinsic background in scintillator detectors in Dark Matter searches

Transcription

1 Sensitivity, performance, stability and intrinsic background in scintillator detectors in Dark Matter searches *A.J.Lerner WONDER 2010, LNGS A.Incicchitti INFN Roma

2 What seest thou else In the dark backward and abysm of time? W. Shakespeare "The Tempest", Act 1 scene 2 A few of history...

3 Li Eu(BO ) LiI(Eu) Long-lasting innovation new developments NaI(Tl) 106 CdWO 4

4 The father of crystal fabrication technology is A.Verneuil with his flame-fusion growth method He can be regarded as the founder of crystal growth technology. For the growth of single crystals there must be a unique nucleus.the simplest method is a prepared seed. It is usually cut from the same crystal. Crystal Growth The principles of the Verneuil method with nucleation, growth rate and diameter control have been applied in most of the growth processes described in the following years. It is possible to grow single crystals: from melts, from solutions, from gas phase, by phase transformations in solid phase. Almost all crystal growth methods use the principle of oriented crystallization. Its basic feature is the balance of two different processes:heat transfer and crystal interface transfer. The implementation of a growing method is characterized by technological features, equipment design and phase diagram peculiarities.

5 Main methods Horizontal growth methods: Bridgeman, Stockbarger, Bagdasarov etc. The crucible is moved through the thermal gradient zone, where the temperature is lowered below the melting point. Here the crystallization takes place. The volume of the melt will therefore decrease continuously and the growing crystal starts substituting for the melt. Czochralski The crystal is pulled from the melt. The seed crystal and crucible are rotated in opposite directions while withdrawal occurs. Kyropoulos Direct crystalization of the melt by decreasing the boule s temperature while it is still in the crucible.

6 Advantages Drawbacks Bridgman Stockbarger Czochralski Technically the simplest method for alkali halide crystals No direct contact of the growing crystal with the crucible walls. Allows an increase in crystal growth rate of several times owing to a higher axial and radial temperature gradients and due to an intensive mixing of the melt by the rotating crystal. Seems to be the most efficient when crystals are required with high structural perfection. Direct contact of the crystal with the crucible walls. Additional stresses in the growing crystal. Difficult extraction of the grown crystal (cracks). Extremely difficult to attain the uniform activator distribution through the single-crystal ingot, i.e. only a fraction of the ingot can be generally used. Insufficient convectional melt mixing before the crystallization front (i.e. inclusions and striations). Spontaneous crystallization on the ampoule surface; as a result, the orientation of the crystal is difficult to control, a well-oriented seed is needed. More complicated technically; permanent control and correction of the main parameters needed. If non automated pulling the success of growth is defined mainly by the skill of the operator. Kyropoulos No direct contact of the growing crystal with the crucible walls. Highly controlled thermal gradient keeps a low-stress environment for the crystal. Again a deep control of all the parameters Implementations of Czochralski -- Kyropoulos techniques are operative and in evolution Commercially produced e.g. NaI(Tl), CsI(Na), CsI(Tl), CsI(pure) single crystal up to 600 mm in diameter and up to 750 mm in height. The total weight of such ingots reaches kg.

7 Chemical complexity (gaseous and liquid solutions, melts) + phase transformation (changes of chemical, structural and density aspects). Scaling problem with the need to control the solid-liquid interface shape on an nm-scale within a growth system of meter dimension, with the corresponding time and energy scales. A further complication is the number of growth parameters (geometrical, thermal, chemical, supersaturation, and hydrodynamic parameters) and their nonlinear interrelations. Also nonstoichiometry, i.e. deviation from congruent melting composition, and impurities often have a significant impact on the crystal-growth processes. Crystal growth technology, especially for scientific applications, will be of still greater importance as demands for crystal sizes, structural perfection, light yield, homogeneity of optical properties, purity of the initial materials, activator distribution uniformity, stoichiometric composition and minimum concentration of point and linear defects are required. Therefore not only the growth processes, but also the crystal machining, the surface preparation, the environment, the protocols have to be deeply studied and then optimized.

8 The times they are a-changin B. Dylan What can we learn from the present?

9 Crystal scintillators in DM and ββ investigation Experiment Target Type Status Site ANAIS NaI annual modulation construction Canfranc DAMA/NaI NaI PSD/annual modulation concluded LNGS DAMA/LIBRA NaI annual modulation running LNGS DAMA/1 ton NaI annual modulation R&D LNGS ELEGANT V NaI ββ concluded Kamioka LSM NaI PSD concluded LSM NAIAD NaI PSD concluded Boulby PICO-LON NaI segmentation test module Oto KIMS CsI PSD/annual modulation running Y2L(Korea) TEXONO CsI neutrino phys. running KS Lab CaF 2 -kamioka CaF 2 DM concluded Kamioka CANDLES CaF 2 ββ and DM running Kamioka DAMA-CaF 2 CaF 2 ββ and DM concluded LNGS ELEGANT VI CaF 2 ββ and DM concluded Oto Alkali halide scintillators are also widely used for nuclear medicine (NaI(Tl)), high-energy physics (CsI(Tl), CsI pure), geophysics (NaI(Tl), CsI(Na)), environment and security control (CsI(Tl), 6 LiI(Eu)) and others. In recent years new Li-based halide scintillators (for example, LiBaF 3 ) are under investigation. ββ decay modes Possible CNC processes Matter stability Dark Matter candidates of various nature Solar axions Etc Electron stability Rare nuclear decay modes Search for exotics in cosmic rays Leader role in investigation of rare processes

10 An example: scintillators by DAMA and by DAMA+INR-Kiev mainly to investigate ββ decay modes with source=detector approach CaF 2 (Eu) Bicron/Crismatec(Saint Gobain) NPA 705 (2002) 29 NPB 563 (1999) 97 CeF 3 Crystal Clear coll. or China NIMA 498 (2003) 352 NCIMA 110 (1997) 189 BaF 2 China or Bicron/Saint Gobain NIMA525 (2004) 535 to appear LiF(W) Ukraine NPA 806 (2008) 388 ZnWO 4 Ukraine NPA 826 (2009) 256 to appear on Acta Physica Polonica A (OMEE-09) PLB 658 (2008) 193 LaCl 3 (Ce) Saint Gobain Ukr. J. of Phys.51 (2006) 1037 NIMA555 (2005) 270 CeCl 3 Iltis/Saint Gobain NPA 824 (2009) 101 and to appear Li 2 MoO 4 Ukraine NIMA 607 (2009) 573 Li 6 Eu(BO 3 ) 3 Ukraine NIMA572 (2007) 734 CdWO 4 Ukraine dev.towards EPJA 36 (2008), 167 PRC 76 (2007) CdWO 4 Ukraine in measurement in DAMA/R&D, to appear 116 CdWO 4 Ukraine in construction and also polycrystalline powder. ZnS(Ag) Saint-Gobain to appear

11 High radiopurity reachable? Powder samples selection by: low background Ge deep underground Mass and atomic absorption spectrometry Neutron activation Selection of growing processes Additives selection Study of standard and non-standard contaminants Chemical/physical purification of selected materials Growing protocols Handling protocols Other materials selection: housing, optical grease, light guides Assembling, transport, storage protocols Prototypes tests OK NO This needs many years of long and difficult work, many specific experience and time. Similar developments and measurements are themselves difficult experiments, etc. Produce detectors for Physics and Astrophysics, but each one will have its own radio-purity

12 Radioactive contamination of crystal scintillators (mbq/kg) arxiv: [nucl-ex] Radiopurity of crystal scintillators DAMA+INR Kiev INR Kiev & DAMA+INR Kiev < DAMA/LIBRA KIMS DAMA ELEGANT VI The highest sensitivity to measure internal contamination of crystal scintillators can be achieved in low background measurements where a scintillator is operating as a detector Time-amplitude analysis Pulse-shape discrimination Energy spectra analysis

13 Why and which NaI(Tl)? Qualification of NaI(Tl) nat K (ppb) U (ppt) Th (ppt) Method of production Standard 2000 < 500 < 500 Bridgman standard growth Low Background < 500 < 500 < 500 Very Low Background Ultra Low Background (project Gran Sasso) < 100 < 50 < 50 << 40 < 5 < 5 K Selected batches Bridgman growth K, U+Th Selected batches (CL, BL) + Kyropoulos growth Purified raw materials NaI and TlI + Crafted Kyropoulos growth + Handling protocol There are two necessary conditions imposing the choice of such inorganic scintillator for ultra-low background: a) the matrix elements of composition do not contain long lived isotopes b) the level of impurities generating natural radioactivity incorporating the crystals have to be sufficiently low (better than ppt) Kyropoulos crystallization process (in platinum crucible when growing for final detectors) acts as an additional considerable purification step determination with the highest sensitivity by measurements with the detectors deep underground VLB and ULB: long and delicate work, far from standard commercial production

14 Some on residual contaminants in new NaI(Tl) detectors e α α/e pulse shape discrimination has practically 100% effectiveness in the MeV range The measured α yield in the new DAMA/LIBRA detectors ranges from 7 to some tens α/kg/day Second generation R&D for new DAMA/LIBRA crystals: new selected powders, physical/chemical radiopurification, new selection of overall materials, new protocol for growing and handling live time = 570 h Th residual contamination From time-amplitude method. If 232 Th chain at equilibrium: it ranges from 0.5 ppt to 7.5 ppt 238 U residual contamination First estimate: considering the measured α and 232 Th activity, if 238 U chain at equilibrium 238 U contents in new detectors typically range from 0.7 to 10 ppt 238 U chain splitted into 5 subchains: 238 U 234 U 230 Th 226 Ra 210 Pb 206 Pb Thus, in this case: (2.1±0.1) ppt of 232 Th; (0.35 ±0.06) ppt for 238 U and: (15.8±1.6) µbq/kg for 234 U Th; (21.7±1.1) µbq/kg for 226 Ra; (24.2±1.6) µbq/kg for 210 Pb. nat K residual contamination The analysis has given for the nat K content in the crystals values not exceeding about 20 ppb double coincidences 129 I and 210 Pb 129 I/ nat I for all the new detectors For details and other information 210 Pb in the new detectors: (5 30) µbq/kg. see NIMA592(2008)297 No sizeable surface pollution by Radon daugthers, thanks to the new handling protocols

15 Shield from environmental radioactivity Heavy passive shield: Cu/Pb/Cd-foils/polyethylene/paraffin shield PMTs surrounded by shaped low-radioactive copper shields Materials selected for low radioactivity, underground since many years Pb and Cu etching and handling in clean room Multi-level system to exclude Radon (and flux with HP N 2 gas) Advantages Example: residual radioactivity in some components of the DAMA/LIBRA passive shield (95% C.L.) Compact, stable on long term, with fixed conditions on radiopurity and costs Fixed shielding efficiency Easily to manage in case of crystal scintillators for calibrations etc... A detector s array already works as an active shield Cosmic muons give negligible contribution in the very low energy region and can be identified in a system with many detectors. Similar arguments still hold also for environmental neutrons Active liquid shields in future experiments? Not competitive, suitable running conditions not assured for DM annual modulation, high costs etc...

16 PMTs Examples of residual radioactivity in PMTs and light guides DAMA/LIBRA (Suprasil B): <0.012 Bq/kg 238 U; <0.008 Bq/kg 232 Th; <0.041 Bq/kg 40 K DAMA/LIBRA PMTs (Il Nuov.Cim.A112(1999)545): 0.37 Bq/kg 238 U; 0.12 Bq/kg 232 Th; 1.9 Bq/kg 40 K New DAMA/LIBRA PMTs TEST on 16 new prototypes (Hamamatsu R6233MOD): 238 U: Range=[0.34,0.54] Bq/kg <0.40 accepted 232 Th: Range=[0.06,0.12] Bq/kg <0.08 accepted 40 K: Range=[0.29,0.91] Bq/kg < 0.35 accepted R&D for new concept PMTs low background PMTs without any glass & ceramics material selection and assembling techniques, 2 prototypes built and qualified: first prototype: second prototype: 40 K < Bq/kg 40 K < Bq/kg 238 U: (0.062 ±0.012) Bq/kg 238 U: (0.248 ±0.012) Bq/kg 232 Th: (3.6 ± 0.8) mbq/kg 232 Th: (8.9 ± 0.8) mbq/kg but electric performances need inprovements PMT+HV divider in future: optimization of the electric performances for low energy further radiopurity improvements (mainly U/Th) increasing the photocatode dimension

17 NaI(Tl) CsI(Tl) CsI(Na) CaF 2 (Eu) CdWO 4 Density [g/cm3] Melting point [K] Thermal expansion coefficient [C -1 ] x x x x x10-6 Cleavage plane <100> none none <111> <010> Hardness (Mho) Hygroscopic yes slightly yes no no Wavelength of emission max. [nm] Refractive emission max Primary decay time [ns] Photoelectron yield [%NaI γ] The light collection optimization is user dependent and has to be made on a case by case basis. A good light collection scheme should: maximize the number of photons extracted keep a good linearity and uniformity of the response. Light collection some impurities and imperfections present in a crystal at the level of a few ppm may influence the optical quality and increase the afterglow. important parameters: form and size of the crystal crystal surface treatment reflecting materials bond scintillator photoreceiver Even more for DM application

18 Threshold threshold (kev) (cpd/kg/kev) σ/e p.e./kev ANAIS NAIAD %@ 60 kev DAMA/LIBRA %@ 60 kev LSM %@ 60 kev 9 KIMS %@ 60 kev 5 CaF 2 Kamioka %@ 5.9 kev 4 DAMA-CaF %@ 60 kev - KIMS 5 th patras workshop 2009 CaF 2 Kamioka PLB623(2006)195 Altri spettri

19 In DM investigation: high number of phe/kev is important to reach low threshold uniformity and linearity are foundamental to have the full control of the detector response Uniformity of the light collection An example: DAMA/LIBRA Absence of dead spaces in the light collection: no significant variations of the peak position and energy resolution when irradiating the whole detector with high-energy γ sources (e.g., 137 Cs) from different positions. α peaks at high energy and their energy resolutions are well compatible with those expected for γ calibration (ex: energy resolution σ = (75±3) kev for α 1, for γ s is 72 kev). All this supports the uniformity of the light collection within 0.5%. Photoelectrons/keV Typical experimental distribution of the area of the single photoelectron s pulses for a DAMA/LIBRA detector A clean sample of photoelectrons can be extracted from the end part of the Waveform Analyser time window (2048 ns) where afterglow single photoelectron signals can be present. The relative peak value can be compared with the peak position of the distribution of the areas of the pulses corresponding to a full energy deposition from the 59.5 kev of the 241 Am phe/kev from 5.5 to 7.5 depending on the detector

20 DAMA/LIBRA calibrations Low energy: various external γ sources ( 241 Am, 133 Ba) and internal X-rays or γ s ( 40 K, 125 I, 129 I), routine calibrations with 241 Am Linearity Energy resolution 3.2 kev Internal 40 K Tagged by an adjacent detector 59.5 kev Internal 125 I first months 40.4 kev 67.3 kev 81 kev 241 Am 133 Ba 30.4 kev σ LE E ( ± 0.035) 3 ( ) 10 = + ± E( kev ) High energy: external sources of γ rays (e.g. 137 Cs, 60 Co and 133 Ba) and γ rays of 1461 kev due to 40 K decays in an adjacent detector, tagged by the 3.2 kev X-rays Linearity Energy resolution 137 Cs 662 kev 1173 kev 1332 kev 60 Co 2505 kev 133 Ba 356 kev 1461 kev 81 kev σ HE E ( 1.12 ± 0.06) 4 ( 17 23) 10 = + ± E( kev ) The signals (unlike low energy events) for high energy events are taken only from one PMT 40 K

21 NDM2003 Example of scintillation energy spectra measured by various NaI(Tl) detectors Shapes/scintillation rates quite different All of them cannot be easily/uniquely simulated by a MC code Modane 1999 poor noise rejection although high n. of ph.e. Astrop.Phys.11(1999) kg NaI(Tl) 83d NAIAD kg NaI(Tl) 181d NAIAD kg NaI(Tl) 117d ELEGANT 2003 ANAIS Astrop.Phys.5(1996)249 PRD56(1997) x 10.7kg NaI(Tl) Astrop.Phys.19(2003)691 NPB114(Proc.Supp)(2003) kg NaI(Tl) old technology

22 Cumulative low-energy distribution of the single-hit scintillation events Single-hit events = each detector has all the others as anticoincidence ( Differences among detectors are present depending e.g. on each specific level and location of residual contaminants, on the detector s location in the 5x5 matrix, etc.) experimental energy threshold DAMA/LIBRA (6 years) total exposure: 0.87 ton yr Efficiencies already accounted for About the energy threshold: The DAMA/LIBRA detectors have been calibrated down to the kev region. This assures a clear knowledge of the physical energy threshold of the experiment. It profits of the relatively high number of available photoelectrons/kev (from 5.5 to 7.5). 3.2 kev, tagged by 1461 kev γ in an adjacent detector The two PMTs of each detector in DAMA/LIBRA work in coincidence with hardware threshold at single photoelectron level. Effective near-threshold-noise full rejection. The software energy threshold used by the experiment is 2 kev.

23 QUENCHING FACTOR examples of q measurement in some detectors with neutrons Ex. of different q determinations for Ge Astrop.Phys.3(1995)361 differences are often present in different experimental determinations of q for the same nuclei in the same kind of detector e.g. in doped scintillators q depends on dopant and on the impurities/trace contaminants; in LXe e.g. on trace impurities, on initial UHV, on presence of degassing/releasing materials in the Xe, on thermodynamical conditions, on possibly applied electric field, etc. Some time increases at low energy in scintillators (dl/dx) and more +PRC(2010) &refs (80-130) 0.87±0.10 (20-100) 0.91±0.03±0.04 Quenching factor is a relevant experimental parameter for DM candidates inducing nuclear recoils. It has to be considered in all kinds of detectors. In additional the channelling effect has to be included when dealing with q in crystals (Eur. Phys. J. C 53(2008)205,J. Phys.: Conf. Ser. 203(2010)012042)). Interesting arguments in arxiv: [nucl-ex].

24 STABILITY Crystal scintillators allow: 1) well controlled operational conditions and monitoring; 2) high reproducibility, high stability, etc. (they do not require re-purification or cooling down/warming up procedures); 3) high duty cycle. However, the stability of the running conditions has to be continuously monitored along all the data taking in order to point out the small effects induced by DM particles such as diurnal or annual modulation, directionality, etc. (i.e. needed stability < 1% or even more). An example: DAMA/LIBRA-6 Operating Temperature HP Nitrogen flux R Hj = hardware rate of j-th detector above single p.e. DAMA/LIBRA-5-6 σ=0.5% 2-8 kev σ = 0.4 % Radon external to the shield HP N 2 Pressure in the inner Cu box and more: the energy scale, the efficiencies Running conditions stable at level < 1%

25 Pulse Shape Discrimination (PSD) DAMA/NaI PLB389(1996)757 data vs Compton electrons Recoil/electron different pulse decay times in scintillators experimental energy spectrum for one crystal a) residual rate after PSD above 4 kev b) residual rate after combined PSD from all the crystals NAIAD Astrop. Phys.19(2003)111 KIMS PRL99(2007) but, these use the combination of upper limits from data subsets which always gives a better limit, since it is not considered either the possible presence of a signal and/or the correct handling of systematics

26 Any e.m. rejection technique is not a DM signature and it is blind to some candidates. Only a statistical discrimination is possible because, e.g., of tail effects from the two populations and of known concurrent processes (e.g., end-range alphas and neutrons induce signals indistinguishable from recoils) whose contribution cannot be estimated and subtracted in any reliable manner at the needed level of precision. PSD cannot safely be applied in the investigation of the DM annual modulation signature; in fact, the effect searched for (at level of few %) would be largely affected by the uncertainties associated to rejection procedure. On the other hand the annual modulation signature acts itself as an effective background rejection. PSD sensitivity vs collected statistics σ syst limits the sensitivity of PSD when going towards large statistics; it depends on several factors: temperature variation during data taking, instrumental effects, stability of the selecting windows,... PSD Observed annual modulation effect in terms of S 0 for a particular model framework sensitivity, 90% CL (cpd/kg) 2-4 kev bin σsyst =0.5 ns σ syst =0.4 ns σ syst =0.3 ns Whatever e.m. rejection technique has similar drawbacks Stat (x1000 kg day)

27 A model independent signature is needed Crystal scintillators: a reliable technology to investigate model independent signatures High duty cycle Well controlled operational conditions Reproducibility (no re-purification procedures or cooling down/warming up) Long term stability Effective routine calibrations down to kev in the same conditions as production runs Sensitive to many candidates, interaction types and astrophysical, nuclear and particle physics scenarios June 30 km/s ~ 232 km/s km/s December Annual modulation Annual variation of the interaction rate due to Earth motion around the Sun. Directionality Correlation of Dark Matter impinging direction with Earth's galactic motion due to the distribution of Dark Matter particles velocities (anisotropic scintillator) Diurnal modulation Daily variation of the interaction rate due to: i) different Earth depth crossed by the Dark Matter particles; ii) Earth rotational velocity (channeling, anisotropy, ecc.)

28 Investigating the presence of a DM particle component in the galactic halo by the model independent annual modulation signature Drukier, Freese, Spergel PRD86 Freese et al. PRD88 June 30 km/s Requirements: ~ 232 km/s 60 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) 30 km/s December 5) Just 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 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) v (t) = v sun + v orb cosγcos[ω(t-t 0 )] dr S k [η(t)] = de R S 0,k + S m,k cos[ω (t t 0 )] de R E k Expected rate in given energy bin changes because of the Earth s motion around the Sun moving in the Galaxy To mimic this signature, spurious effects and side reactions must not only be able to account for the whole observed modulation amplitude, but also to satisfy contemporaneously all the requirements The DM annual modulation effect has different origins and, thus, different peculiarities (e.g. the phase) with respect to those effects connected with the seasons instead

29 Dark Matter investigation by model-independent annual modulation signature DAMA/NaI (7 years) + DAMA/LIBRA (6 years). Total exposure: 1.17 ton yr (the largest exposure ever collected in this field) Experimental single-hit residuals rate vs time in 2-6 kev EPJC 56(2008)333, arxiv: Power spectrum Principal mode d -1 1 y kev 6-14 kev Acos[ω(t-t 0 )] continuous lines: t 0 = d, T = 1.00 y A=(0.0114±0.0013) cpd/kg/kev χ 2 /dof = 64.7/ σ C.L. Absence of modulation? No χ 2 /dof=140/80 P(A=0) = fit with all the parameters free: A = ( ± ) cpd/kg/kev t 0 = (146±9) d T = (0.999±0.002) y Comparison between single hit residual rate (red points) and multiple hit residual rate (green points) for (DAMA/LIBRA 1-6); Clear modulaion in the single hit events A=(0.0091±0.0014) cpd/kg/kev; No modulation in the residual rate of the multiple hit events A=-(0.0006±0.0004) cpd/kg/kev 2-6 kev No systematics or side reaction able to account for the measured modulation amplitude and to satisfy all the peculiarities of the signature Multiple hits events = Dark Matter particle switched off The data favor the presence of a modulated behaviour with all the proper features for DM particles in the galactic halo at about 9σ9 C.L. This result offers an additional strong support for the presence of DM particles in the galactic halo further excluding any side effect either from hardware or from software procedures or from background

30 Example of sensitivity under some assumptions ASSUMPTIONS CsI scintillator (100 kg) 3 years of data taking (60% duty cycle) Mandatory hypothesis: stability of the set-up <<1% mean eff. = 0.4 Iodine quenching factor and channelling as in DAMA IF DAMA signal were due just to Sodium recoils insensitive E.g. assuming some model: expected modulation amplitudes and cpd/kg/kev, in the [4,6] and [3,6] kev respectively IF DAMA signal were due just to Iodine recoils: Fitted modulation amplitudes: -(0.004±0.014) cpd/kg/kev in [4,6] kev (expected ) (0.0029±0.0082) cpd/kg/kev in [3,6] kev (expected ) rate: 2. cpd/kg/kev 3. cpd/kg/kev 5. cpd/kg/kev Residuals (cpd/kg/kev) KIMS 5 th patras workshop [4,6] kev [3,6] kev 0.45 Examples by MC simulation in CsI E th =4 kev; counting rate = 5 cpd/kg/kev E th =3 kev; counting rate = 2.5 cpd/kg/kev Critical dependence on energy threshold, counting rate, stability etc. The sensitivity of such an experiment is not enough to see the DAMA signal Time(d)

31 Example of sensitivity under some assumptions ASSUMPTIONS NaI scintillator (100 kg) (ANAIS) 3 years of data taking (60% duty cycle) same response to recoils and to e.m. DM as for DAMA Mandatory hypothesis: stability of the set-up <<1% mean eff. = 0.7 E th = 4 kev, 3 kev Fitted modulation amplitudes: -(0.005±0.011) cpd/kg/kev in [4,6] kev (expected ) (0.0001±0.0056) cpd/kg/kev in [3,6] kev (expected ) measured rate: 2. cpd/kg/kev 3. cpd/kg/kev 5. cpd/kg/kev Residuals (cpd/kg/kev) [4,6] kev [3,6] kev Examples by MC simulation in NaI E th =4 kev; counting rate = 5 cpd/kg/kev E th =3 kev; counting rate = 2 cpd/kg/kev Time(d) Critical dependence on energy threshold, counting rate, stability etc. The sensitivity of such an experiment is not enough to see the DAMA signal

32 If to do were as easy as to know what were good to do, W. Shakespeare "The Merchant of Venice", Act 1 scene 2 Forward to the future

33 ... towards a 100 ton highly radiopure NaI(Tl) set-up for high-resolution full-spectroscopy solar neutrinos (Astrop.Phys.4(1995)45) see ApPEC document: R. Bernabei spokesperson Goals of high-mass and high-sensitivity NaI detector: Extremely high C.L. for the model independent signal Model independent investigation on other peculiarities of the signal High exposure: investigation & test of different astrophysical, nuclear, particle physics models Increasing the competitiveness in DM investigation with respect to DAMA/LIBRA Further investigation on Dark Matter candidates (further on neutralino, bosonic DM, mirror DM, inelastic DM, neutrino of 4 th family, etc.): high exposure can better disentangle among the different astrophysical, nuclear and particle physics models (nature of the candidate, couplings, inelastic interaction, particle conversion processes,, form factors, spin-factors and more on new scenarios) scaling laws and cross sections multi-component DM particles halo? + Further investigation on astrophysical models: velocity and position distribution of DM particles in the galactic halo effects due to: i) satellite galaxies (as Sagittarius and Canis Major Dwarves) tidal streams ; ii) caustics in the halo; iii) gravitational focusing effect of the Sun enhancing the DM flow ( spike and skirt ); iv) possible structures as small scale size clumpiness; Also high sensitivities investigation on other rare processes: possible PEP violating processes, various possible CNC processes in 23 Na and 127 I, nucleon and di-nucleon decay into invisible channels with new approach in 23 Na and 127 I, exotic particles (e.g. SIMPs, neutral nuclearities, Q-balls), solar axions by Primakoff effect in NaI(Tl), rare nuclear processes in 23 Na, 127 I, hypothesized neutral particles (new QED phase) in 241 Am decays, etc.

34 An example of possible signature for the presence of streams in the Galactic halo The effect of the streams on the phase depends on the galactic halo model Phase (day of maximum) 2σ band Example, NaI: 10 tons yr E (kev) DAMA/NaI&DAMA/LIBRA results: (2-6) kev t 0 = (146±7) d Expected phase in the absence of streams t 0 = d (2 nd June) Evans log axisymmetric non-rotating, v 0 =220km/s, R c = 5kpc, ρ 0 max + 4% Sgr NFW spherical isotropic non-rotating, v 0 =220km/s, ρ 0 max + 4% Sgr The higher sensitivity of DAMA/1ton will allow the further investigation of possible contribution of streams in the galactic halo in shorter time Eur. Phys. J. C 47(2006) 263

35 Effect of Solar gravity for DM streams The Sun gravity can focus the DM flux producing two type of enhancements in the density: spike collinear to the direction of incidence between DM flux and Sun, skirt divergence on a cone of angle θmax PRD66(2002) PRD70(2004) The presence of SKIRT can be investigated by observing an increase in the counting rate in a time interval of 1 day With large exposure and low energy threshold you can be sensitive to small fraction ( ) of flow density with respect to the halo density

36 INVESTIGATION OF POSSIBLE DIURNAL EFFECTS daily effect on the sidereal time expected in case of DM candidates inducing nuclear recoils in anisotropic scintillator daily effect on the sidereal time expected in case of high cross section DM candidates (shadow of the Earth) daily modulation on the sidereal time due to the Earth rotation velocity contribution (it holds for a wide range of DM candidates) daily effect on the sidereal time due to the channeling in case of DM candidates inducing nuclear recoils.

37 DIURNAL EFFECTS daily effect on the sidereal time: DM candidates inducing nuclear recoils in anisotropic scintillator Correlation of the track of the nuclear recoil with Earth s motion in the Galactic halo Crystals as anthracene, C 14 H 10 and stilbene C 14 H 12 Investigation with organic anisotropic scintillator? (N.Cim.15C(1992)475, EPJC28 (2003)203 +Int. Workshop on Identification of Dark Matter, World Scientific (1997) 481, PLB571 (2003)132,NIMA496(2003)347) q q q q c' b c' a light anisotropy for recoil nuclei and no anisotropy for electrons; anisotropy greater at low energy. Example: Light response of anthracene relative to heavy ionizing particles depends on their impinging direction with respect to the crystal axes. The diurnal Earth rotation changes the impinging direction of the DMp flux (and the mean direction of the recoil nuclei induced by DMp) with the respect to the crystal axes. Larger anisotropic scintillators?

38 DIURNAL EFFECTS daily effect on the sidereal time: high cross section DM candidates (shadow of the Earth) Daily variation of the interaction rate due to different Earth depth crossed by the DMp PLB275(1992)181 θ vs Sidereal time Only for large cross sections Investigation in DAMA/NaI-2 data (N.Cim. A112(1999)1541): kg d Study on diurnal variation in the rate with suitable exposure and stability can allow to investigate: Limits on halo fraction (ξ) vs σ p for SI case in the given model high σ p DMp component (with small ξ) in the dark halo and decouple ξ from σ p

39 DIURNAL EFFECTS Velocity of the detector in the galactic frame: daily modulation on the sidereal time: due to the Earth rotation velocity contribution (wide range of DM candidates) Phys. Atom. Nucl. 72 (2009)2076 annual modulation term diurnal modulation term Expected signal counting rate in a given k-th energy bin: angle beetwen the Earth axis and the DM flux d s = 1 sideral day t d = phase depending on detector longitude LNGS latitude This signature can allow a powerful decoupling from the models. The ratio of the diurnal modulation amplitude over the annual modulation amplitude is a fully model-independent constant However, considering the annual modulation amplitude observed in DAMA (in the (2-6) kev roughly cpd/kg/kev) the expected diurnal modulation amplitude is cpd/kg/kev This amplitude can be investigated either when a much larger exposure will be available (e.g. many years of running of DAMA/1ton) or with 10 tons set-up in few years. Much better sensitivities can be reached if the energy threshold is decreased to 1 kev.

40 DIURNAL EFFECTS Eur. Phys. J. C 53(2008)205 daily effect on the sidereal time: due to the channeling in case of DM candidates inducing nuclear recoils. x y ˆ v earth xˆ z Due to the Earth daily rotation with respect to the Galactic Frame, the orientations of the crystallographic axes (c.a.) changes during sideral day The DM signal varies during the day depending on the orientation of the c.a. If DM induces recoils, from DAMA results we expect roughly cpd/kg/kev. Mass = 8 GeV R max /R = 0.18 % Maximum amplitude range within the sidereal day in (2-6 kev) Percentage variation of the Rate in the sideral day (2-6 kev) Mirror DM This amplitude can be investigated either when a much larger exposure will be available (e.g. many years of running of DAMA/1ton) or with 10 tons set-up in few years. Much better sensitivities can be reached if the energy threshold is decreased to 1 kev and/or in case of Mirror DM candidates.

41 Maximum amplitude range within the sidereal day in (2-6 kev) blu:cold Stream: a caustic halo model Caustic Halo model: ρ 0 = 0.84 GeV/cm 3 velocity distribution: stream with v x = 120 km/s, v y = 505 km/s, v z = 0 km/s assumed here: v earth = 232 km/s red:nfw model NFW model Isothermal model ρ 0 = 0.3 GeV/cm 3 quasi-isotropic velocity distribution v 0 = 220 km/s, v esc = 650 km/s Cyan: A0 halo model ρ 0 = 0.3 GeV/cm 3 maxwellian velocity distribution v 0 = 220 km/s, v esc = 650 km/s green: halo model by Aquarius Project Aquarius model (Aq-A-2) velocity distribution: see picture v km/s

42 NEUTRINO PHYSICS with MultiTon NaI(Tl) set-up Very low background Multi-ton ton NaI(Tl) ) set-up can also give interesting results on neutrinos (Astrop.. Phys.4(1995)45,Astrop.Phys.8(1997)67, Nucl.Phys.B546(1999)19, New Journal of Physics 3(2001)5.1) Solar neutrinos spectroscopy from ν e -Na and ν e -I real time interactions Investigation on ν oscillation from low energy, large activity artificial ν source ( 147 Pm) Investigation on ν magnetic moment (artificial ν source) Search for new physics in neutrino interaction

43 ...Last... Solid, well-known and evergreen detectors widespread in many fields and application Crystal scintillators & scintillation technique Continuous improvements in performance and radiopurity achieved with time passing technology constantly in development Competitive and profitable choice for future experiments on rare processes

44 Conclusions ULB ULB inorganic inorganic crystal crystal scintillators scintillators are are powerful powerful tools tools to to investigate investigate rare rare processes processes ULB ULB NaI(Tl) NaI(Tl) has has been been succesfully succesfully used used by by DAMA/NaI DAMA/NaI and and DAMA/LIBRA to to investigate investigate a a particle particle Dark Dark Matter Matter component component in in the the galactic galactic halo halo exploiting exploiting the the annual annual modulation modulation signature signature Ultimate Ultimate developments of of low low background background techniques techniques in in crystal crystal scintillators scintillators and and related related set-ups set-ups will will further further enlarge enlarge the the frontier frontier of of investigation in in rare rare processes processes If you can look into the seeds of time, And say which grain will grow and which will not, Speak then to me, who neither beg nor fear Your favours nor your hate. W. Shakespeare "Machbeth" Act 1, scene 3