A.IncicchittiINFN Roma

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

WONDER 2010, LNGS*A.J.Lerner

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

A few of history........

Long-lasting innovationLong-lasting innovation

106CdWO4

new developments

LiI(Eu)

NaI(Tl)

Li6Eu(BO3)3

The father of crystal fabrication technology is A.Verneuil with his flame-fusion growth method 1902. He can be regarded as the founder of crystal growth technology.

The father of crystal fabrication technology is A.Verneuil with his flame-fusion growth method 1902. He can be regarded as the founder of crystal growth technology.

The principles of the Verneuilmethod with nucleation, growth rate and diameter control have been applied in most of the growth processes described in the following years.

Crystal GrowthCrystal Growth

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.

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.

It is possible to grow single crystals: from melts, from solutions, from gas phase, by phase transformations in solid phase.

Main methodsMain methods

Horizontal growth methods: Bridgeman, Stockbarger, Bagdasarovetc.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.

CzochralskiThe crystal is pulled from the melt. The seed crystal and crucible are rotated in opposite directions while withdrawal occurs.

KyropoulosDirect crystalization of the melt by decreasing the boule’s temperature while it is still in the crucible.

Advantages DrawbacksAdvantages Drawbacks

Bridgman–StockbargerTechnically the simplestmethod for alkali halide crystals

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.Czochralski

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.

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

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 400–500 kg.

Implementations of Czochralski -- Kyropoulos techniques are operative and in evolution

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, stoichiometriccomposition 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.

The times they are a-changin’B. Dylan

What can we learn from the present?

ExperimentExperiment TargetTarget TypeType StatusStatus SiteSiteANAIS NaI annual modulation construction CanfrancDAMA/NaI NaI PSD/annual modulation concluded LNGSDAMA/LIBRA NaI annual modulation running LNGSDAMA/1 ton NaI annual modulation R&D LNGSELEGANT V NaI ββ concluded KamiokaLSM NaI PSD concluded LSMNAIAD NaI PSD concluded BoulbyPICO-LON NaI segmentation test module OtoKIMS CsI PSD/annual modulation running Y2L(Korea)TEXONO CsI neutrino phys. running KS LabCaF2-kamioka CaF2 DM concluded KamiokaCANDLES CaF2 ββ and DM running KamiokaDAMA-CaF2 CaF2 ββ and DM concluded LNGSELEGANT VI CaF2 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), 6LiI(Eu)) and others. In recent years new Li-based halide scintillators (for example, LiBaF3) are under investigation.

Rare nuclear decay modesRare nuclear decay modes

Matter stability Etc…

Solar axionsββ decay modes

Possible CNC processes

Search for exotics in cosmic rays

Dark Matter candidates of various nature

Electron stabilityLeader role in investigation

of rare processes

Crystal scintillators in DM and ββ investigationCrystal Crystal scintillatorsscintillators in DM and in DM and ββββ investigationinvestigation

An example: scintillators by DAMA and by DAMA+INR-Kievmainly to investigate ββ decay modes with source=detector approach

CaF2(Eu) Bicron/Crismatec(Saint Gobain) NPA 705 (2002) 29 NPB 563 (1999) 97

CeF3 Crystal Clear coll. or China NIMA 498 (2003) 352NCIMA 110 (1997) 189

BaF2 China or Bicron/Saint Gobain NIMA525 (2004) 535to appear

LiF(W) Ukraine NPA 806 (2008) 388 ZnWO4 Ukraine NPA 826 (2009) 256

to appear on Acta Physica Polonica A (OMEE-09)PLB 658 (2008) 193

LaCl3(Ce) Saint Gobain Ukr. J. of Phys.51 (2006) 1037NIMA555 (2005) 270

CeCl3 Iltis/Saint Gobain NPA 824 (2009) 101 and to appear

Li2MoO4 Ukraine NIMA 607 (2009) 573

Li6Eu(BO3)3 Ukraine NIMA572 (2007) 734CdWO4 Ukraine dev.towards EPJA 36 (2008), 167

PRC 76 (2007) 064603 106CdWO4 Ukraine in measurement in DAMA/R&D,

to appear116CdWO4 Ukraine in construction

and also polycrystalline powder. ZnS(Ag) Saint-Gobain to appear

Produce Produce detectors for Physics detectors for Physics and and AstrophysicsAstrophysics,,but each but each one one will have its own radiowill have its own radio--puritypurity

High radiopurity reachable?

Powder samples selection by:low background Ge deep underground Mass and atomic absorption spectrometryNeutron 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

This needs many years of long and difficult work, many specific experience and time.Similar developments and measurements are themselves difficult experiments, etc.

OKNO

< DAMA/LIBRA

DAMA

DAMA+INR Kiev

KIMS

INR Kiev &DAMA+INR Kiev

Radiopurity of crystal scintillators

Radiopurity of Radiopurity of crystal scintillatorscrystal scintillators

The highest sensitivity to measure internal contamination of crystal scintillators can be achieved in low backgroundmeasurements where a scintillator is operating as a detector

• Time-amplitude analysis• Pulse-shape discrimination• Energy spectra analysis

ELEGANT VI

arXiv:0903.1539[nucl-ex]

Radioactive contamination of crystal scintillators (mBq/kg)

“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 isotopesb) the level of impurities generating natural radioactivity incorporating the crystals have to be

sufficiently low (better than ppt)”

Qualification of NaI(Tl)

natK (ppb) U (ppt) Th

(ppt) Method of production

Standard 2000 < 500 < 500 Bridgman standard growth

Low Background < 500 < 500 < 500 K Selected batches Bridgman growth

Very Low Background < 100 < 50 < 50

K, U+Th Selected batches (CL, BL)

+ Kyropoulos growth

Ultra Low Background (project Gran Sasso)

<< 40 < 5 < 5

Purified raw materials NaI and TlI +

Crafted Kyropoulos growth + Handling protocol

Why and which NaI(Tl)?Why and which NaI(Tl)?

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

α

e

2

3

4

51

live time = 570 h

Some on residual contaminants in new NaI(Tl) detectorsα/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

232Th residual contamination From time-amplitude method. If 232Th chain at equilibrium: it ranges from 0.5 ppt to 7.5 ppt

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

238U residual contamination First estimate: considering the measured α and 232Th activity, if 238U chain at equilibrium ⇒ 238U contents in new detectors typically range from 0.7 to 10 ppt

238U chain splitted into 5 subchains: 238U → 234U → 230Th → 226Ra → 210Pb → 206Pb

double coincidencesnatK residual contaminationThe analysis has given for the natK content in the crystals values not exceeding about 20 ppb

Thus, in this case: (2.1±0.1) ppt of 232Th; (0.35 ±0.06) ppt for 238Uand: (15.8±1.6) µBq/kg for 234U + 230Th; (21.7±1.1) µBq/kg for 226Ra; (24.2±1.6) µBq/kg for 210Pb.

129I/natI ≈1.7×10-13 for all the new detectors210Pb in the new detectors: (5 − 30) µBq/kg.

129I and 210Pb

No sizeable surface pollution by Radon daugthers, thanks to the new handling protocols

For details and other informationsee NIMA592(2008)297

Shield from environmental radioactivityHeavy 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 N2 gas)

Example: residual radioactivity in some components of the DAMA/LIBRA passive shield (95% C.L.)

Advantages• 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 neutronsActive liquid shields in future experiments? Not competitive, suitable running conditions not assured for DM annual modulation, high costs etc...

PMTs

DAMA/LIBRA (Suprasil B): <0.012 Bq/kg 238U; <0.008 Bq/kg 232Th; <0.041 Bq/kg 40KExamples of residual radioactivity in PMTs and light guides

DAMA/LIBRA PMTs (Il Nuov.Cim.A112(1999)545):≈0.37 Bq/kg 238U; ≈0.12 Bq/kg 232Th; ≈1.9 Bq/kg 40K

New DAMA/LIBRA PMTs TEST on 16 new prototypes (Hamamatsu R6233MOD):

238U: Range=[0.34,0.54] Bq/kg <0.40 accepted232Th: Range=[0.06,0.12] Bq/kg <0.08 accepted

40K: Range=[0.29,0.91] Bq/kg < 0.35 accepted

PMT+HV divider

R&D for new concept PMTslow background PMTs without any glass & ceramicsmaterial selection and assembling techniques, 2 prototypes built and qualified:

first prototype: second prototype:40K < 0.032 Bq/kg 40K < 0.003 Bq/kg

238U: (0.062 ±0.012) Bq/kg 238U: (0.248 ±0.012) Bq/kg232Th: (3.6 ± 0.8) mBq/kg 232Th: (8.9 ± 0.8) mBq/kg

but electric performances need inprovements

in future:optimization of the electric performancesfor low energyfurther radiopurity improvements (mainly U/Th)increasing the photocatode dimension

NaI(Tl) CsI(Tl) CsI(Na) CaF2(Eu) CdWO4

Density [g/cm3] 3.67 4.51 4.51 3.18 7.9

Melting point [K]

924 894 894 1691 1598

Thermal expansion coefficient [C-1]

47.4 x10-6 54 x10-6 54 x10-6 19.5 x10-6 10.2 x10-6

Cleavage plane <100> none none <111> <010>

Hardness (Mho)

2 2 2 4 4-4.5

Hygroscopic yes slightly yes no no

Wavelength of emission max. [nm]

415 550 420 435 475

Refractive index @ emission max

1.85 1.79 1.84 1.47 2.2-2.3

Primary decay

time [ns]

250 1000 630 940 14000

Photoelectron yield [%NaI γ]

100 45 85 50 30-50

some impurities and imperfections present in a crystal at the level of a few ppm may influence the optical quality and increase the afterglow.

Light collectionLight collectionLight collection

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.

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.

Even more for DM application

important parameters:• form and size of the crystal• crystal surface treatment• reflecting materials• bond “scintillator–photoreceiver”

Threshold(keV)

Rate @ threshold

(cpd/kg/keV)σ/E p.e./keV

ANAIS 4 1.2 - -NAIAD 2 10 8.5%@ 60 keV 4.6÷9

DAMA/LIBRA 2 1 6.7%@ 60 keV 5.5÷7.5LSM 2 10 5%@ 60 keV 9KIMS 3 3 8.2%@ 60 keV 5

CaF2 Kamioka 2 10 34%@ 5.9 keV 4DAMA-CaF2 4 8 11%@ 60 keV -

Altri spettri

KIMS 5th patras workshop 2009

CaF2 KamiokaPLB623(2006)195

In DM investigation: high number of phe/keV is important to reach low thresholduniformity and linearity are foundamental to have the full control of the detector response

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., 137Cs) 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 α1, for γ’s is 72 keV).

All this supports the uniformity of the light collection within 0.5%.

Uniformity of the light collection

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.

Typical experimental distribution of the area of the single photoelectron’s pulses for a DAMA/LIBRA detector

phe/keV from 5.5 to 7.5 depending on the detector

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 241Am

Photoelectrons/keV

( ) ( ) 30.448 0.0359.1 5.1 10

( )LE

E E keVσ −±

= + ± ⋅

DAMA/LIBRA calibrationsLow energy: various external γ sources (241Am, 133Ba) and internal X-rays or γ ’s (40K, 125I, 129I), routine calibrations with 241Am

High energy: external sources of γ rays (e.g. 137Cs, 60Co and 133Ba) and γ rays of 1461 keV due to 40K decays in an adjacent detector, tagged by the 3.2 keV X-rays

( ) ( ) 41.12 0.0617 23 10

( )HE

E E keVσ −±

= + ± ⋅

Linearity Energy resolutionLinearity Energy resolution

The signals (unlike low energy events) for high energy events are taken only from one PMT

81 keV

133Ba

Internal 40KTagged by an adjacent detector

Internal 125Ifirst months

241Am

3.2 keV

59.5 keV

67.3 keV

40.4 keV

30.4 keV

Linearity Energy resolution

137Cs 60Co

133Ba

40K

81 keV

662 keV 1173 keV1332 keV

2505 keV

356 keV1461 keV

9.7kg NaI(Tl) 83d

ANAISANAIS PRD56(1997)1856

3 x 10.7kg NaI(Tl)

ELEGANT 2003ELEGANT 2003

NDM2003

Modane 1999Modane 1999

NPB114(Proc.Supp)(2003)111

10.7kg NaI(Tl)

poor noise rejection although high n. of ph.e.

Astrop.Phys.11(1999)287

old technology

6.2kg NaI(Tl) 181d

Astrop.Phys.5(1996)249

8.5kg NaI(Tl) 117d

NAIAD 2003NAIAD 2003NAIAD 1996NAIAD 1996

Astrop.Phys.19(2003)691

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

Cumulative low-energy distribution of the single-hit scintillation events

DAMA/LIBRA (6 years)total exposure: 0.87 ton×yr

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.

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.)

Efficiencies already accounted for

experimental energy threshold

0.87±0.10

examples of q measurement in some detectors with neutrons

(20-100) 0.91±0.03±0.04

(80-130)

+PRC(2010)025808 &refs

QUENCHING FACTORQUENCHING FACTOR

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 detectore.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

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:0911.3041[nucl-ex].

STABILITYSTABILITYCrystal 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).

RHj = hardware rate of j-thdetector above single p.e.

…and more:the energy scale, the efficiencies

An example: DAMA/LIBRA-6σ = 0.4 %2-8 keVDAMA/LIBRA-5-6

σ=0.5%

HP N2 Pressurein the inner Cu box

Operating Temperature

Radon external to the shield

HP Nitrogen flux

Running conditions stable at level < 1%

Pulse Shape Discrimination (PSD) Recoil/electron different pulse decay times in scintillators

data vs Compton electrons

DAMA/NaI PLB389(1996)757

KIMSPRL99(2007)091301

NAIADAstrop. Phys.19(2003)111

...but, these use the combination of upper limits from data subsets whichalways gives a “better” limit, since it is not considered either the possiblepresence of a signal and/or the correct handling of systematics

experimental energy spectrum for one crystal

b) residual rate after combined PSD from all the crystals

a) residual rate after PSD above 4 keV

PSD sensitivity vs collected statistics

2-4 keV bin σsyst=0.5 ns

σsyst=0.4 ns

σsyst=0.3 ns

sens

itiv

ity,

90%

CL

(cpd

/kg)

Stat (x1000 kg day)

PSD sensitivity vs collected statistics

2-4 keV bin σsyst=0.5 ns

σsyst=0.4 ns

σsyst=0.3 ns

sens

itiv

ity,

90%

CL

(cpd

/kg)

Stat (x1000 kg day)

• 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 torejection procedure. On the other hand the annual modulation signature acts itself as an effectivebackground rejection.

• σsyst 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, ...

Observed annual modulation effect in terms of S0 for a particular model framework

PSDPSD

Whatever e.m. rejection technique has similar drawbacks

A model independent signature is neededA model independent signature is needed

Annual modulation Annual variation of the interaction rate due to Earth motion around the Sun.

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.)

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

December30 km/s

~ 232 km/s60°

June30 km/s

Directionality Correlation of Dark Matter impinging direction with Earth's galactic motion due to the distribution of Dark Matter particles velocities (anisotropic scintillator)

Investigating the presence of a DM particle component in the galactic halo by the model independent annual modulation signature

Requirements:

v⊕(t) = vsun + vorb cosγcos[ω(t-t0)]v⊕(t) = vsun + vorb cosγcos[ω(t-t0)]Sk[η(t)] =

dRdER

dER ≅ S0,k +∆Ek

∫ Sm ,k cos[ω (t − t0 )]

Expected rate in given energy bin changes because of the Earth’s motion around the Sun moving in the Galaxy

• vsun ~ 232 km/s (Sun velocity in the halo)• vorb = 30 km/s (Earth velocity around the Sun)• γ = π/3• ω = 2π/T T = 1 year• t0 = 2nd June (when v⊕ is maximum)

• vsun ~ 232 km/s (Sun velocity in the halo)• vorb = 30 km/s (Earth velocity around the Sun)• γ = π/3• ω = 2π/T T = 1 year• t0 = 2nd June (when v⊕ is maximum)

December30 km/s

~ 232 km/s60°

June30 km/s

Drukier, Freese, Spergel PRD86Freese et al. PRD88

1) Modulated rate according cosine2) In a definite low energy range3) With a proper period (1 year)4) With proper phase (about 2 June)5) Just for single hit events in a multi-detector set-up6) 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 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

6-14 keV

2-6 keV

6-14 keV

2-6 keV

Dark Matter investigation by modelDark Matter investigation by model--independent annual modulation signatureindependent annual modulation signature

No No systematicssystematics or side reaction able or side reaction able to account for the measured to account for the measured modulation amplitude and to satisfy modulation amplitude and to satisfy all the peculiarities of the signatureall the peculiarities of the signature

Power spectrum

Multiple hits events = Dark Matter particle “switched off” 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

2-6 keV

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

EPJC 56(2008)333, arXiv:1002.1028

continuous lines: t0 = 152.5 d, T = 1.00 yAcos[ω(t-t0)]

The data favor the presence of a modulated The data favor the presence of a modulated behaviourbehaviour with all the proper with all the proper features for DM particles in the galactic halo at about 9features for DM particles in the galactic halo at about 9σσ C.L.C.L.

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

A=(0.0114±0.0013) cpd/kg/keVχ2/dof = 64.7/79 8.8 σ C.L.

Absence of modulation? Noχ2/dof=140/80 P(A=0) = 4.3×10-5

fit with all the parameters free:A = (0.0098 ± 0.0015) cpd/kg/keVt0 = (146±9) d T = (0.999±0.002) y

Principal mode 2.735 · 10-3 d-1 ≈ 1 y-1

ASSUMPTIONS

•CsI scintillator (100 kg)

•3 years of data taking (60% duty cycle)

•Iodine quenching factor and channelling as in DAMA

• mean eff. = 0.4

[4,6] keV

Res

idua

ls(c

pd/k

g/ke

V)

[3,6] keV

Time(d)

Examples by MC simulation in CsI

Eth=4 keV; counting rate = 5 cpd/kg/keV

Eth=3 keV; counting rate = 2.5 cpd/kg/keV

Fitted modulation amplitudes:-(0.004±0.014) cpd/kg/keV in [4,6] keV (expected ≈ 0.0083)(0.0029±0.0082) cpd/kg/keV in [3,6] keV (expected ≈0.0104)

IF DAMA signal were due just to Iodine recoils:

IF DAMA signal were due just to Sodium recoils →insensitiveE.g. assuming some model: expected modulation amplitudes ≈ 5×10-11 and 3×10-7 cpd/kg/keV, in the [4,6] and [3,6] keV respectively

KIMS 5th patras workshop 2009

0.28 0.450.40

rate:2. cpd/kg/keV3. cpd/kg/keV5. cpd/kg/keV

Mandatory hypothesis: stability of the set-up <<1%

Critical dependence on energy threshold, counting rate, stability etc.

Example of sensitivity under some assumptionsExample of sensitivity under some assumptions

The sensitivity of such an experiment is not enough to see the DAMA signal

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

• mean eff. = 0.7• Eth = 4 keV, 3 keV

Fitted modulation amplitudes:-(0.005±0.011) cpd/kg/keV in [4,6] keV(expected ≈ 0.0070)(0.0001±0.0056) cpd/kg/keV in [3,6] keV(expected ≈ 0.0088)

measured rate:2. cpd/kg/keV3. cpd/kg/keV5. cpd/kg/keV

Examples by MC simulation in NaI

[4,6] keV

Eth=4 keV; counting rate = 5 cpd/kg/keV

[3,6] keV

Res

idua

ls (c

pd/k

g/ke

V)Eth=3 keV; counting rate = 2 cpd/kg/keV

Time(d)

Mandatory hypothesis: stability of the set-up <<1%

Example of sensitivity under some assumptionsExample of sensitivity under some assumptions

Critical dependence on energy threshold, counting rate, stability etc.

The sensitivity of such an experiment is not enough to see the DAMA signal

If to do were as easy as to know what weregood to do, …

W. Shakespeare "The Merchant of Venice", Act 1 scene 2

Forward to the future

Goals of highGoals of high--mass and highmass and high--sensitivity sensitivity NaINaI detector:detector:

•• Extremely Extremely high C.L. high C.L. for for the model the model independent signalindependent signal

•• Model Model independent investigation independent investigation on on other peculiarities other peculiarities of the of the signal signal

•• High High exposureexposure: : investigation investigation & test of & test of different astrophysicaldifferent astrophysical, , nuclearnuclear, , particle physics models particle physics models

see ApPEC document: R. Bernabei spokesperson

Increasing the competitiveness in DM Increasing the competitiveness in DM investigationinvestigation withwith respectrespect toto DAMA/LIBRADAMA/LIBRA

•• Further investigation on astrophysical models:Further investigation on astrophysical models:velocity and position distribution of DM particles in the galactic haloeffects 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;

•• Further investigation on Dark Matter candidates (further Further investigation on Dark Matter candidates (further on on neutralinoneutralino, , bosonicbosonic DM, mirror DM, inelastic DM, DM, mirror DM, inelastic DM, neutrino of 4neutrino of 4thth family, etc.):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 sectionsmulti-component DM particles halo?

+

Also high sensitivities investigation on other rare processes: possible PEP violating processes, various possible CNC processes in 23Na and 127I, nucleon and di-nucleon decay into invisible channels with new approach in 23Na and 127I, exotic particles (e.g. SIMPs, neutral nuclearities, Q-balls), solar axions by Primakoff effect in NaI(Tl), rare nuclear processes in 23Na, 127I, hypothesized neutral particles (new QED phase) in 241Am decays, etc.

... towards a 100 ton highly radiopure NaI(Tl) set-up for high-resolution full-spectroscopy solar neutrinos (Astrop.Phys.4(1995)45)

An example of possible signature for the An example of possible signature for the presence of streams in the Galactic halopresence of streams in the Galactic halo

The effect of the streams on the phase depends on the galactic halo model

Phas

e Ph

ase (

day

of

(day

of m

axim

umm

axim

um))

E (keV)E (keV)

Expected phase in the absence of streams t0 = 152.5 d (2nd June)

NFW spherical isotropic non-rotating, v0=220km/s, ρ0 max + 4% Sgr

Evans’log axisymmetric non-rotating,v0=220km/s, Rc= 5kpc, ρ0 max + 4% Sgr

The higherThe higher sensitivity sensitivity of of DAMA/1tonDAMA/1ton will will allow the further investigation of possible allow the further investigation of possible contribution of contribution of streams in the galactic halostreams in the galactic haloin shorter timein shorter time

DAMA/NaI&DAMA/LIBRA results:(2-6) keV t0 = (146±7) d

Example, NaI: 10 tons×yr

2σ band

Eur. Phys. J. C 47(2006) 263

Effect of Solar gravity for DM streams 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)023504PRD70(2004) 123503

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 (10-3-10-5) of flow density with respect to the halo density

INVESTIGATIONINVESTIGATION

OF POSSIBLEOF POSSIBLE

DIURNAL EFFECTSDIURNAL 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.

daily effect on the sidereal time: DM candidates inducing nuclear recoils in anisotropic scintillator

DIURNAL EFFECTSDIURNAL EFFECTS

• Correlation of the track of the nuclear recoil with Earth’s motion in the Galactic halo

5.1'

≈b

c

qq

2.1'

≈a

c

qq

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)

The diurnal Earth rotation changes the impinging direction of the DMpflux (and the mean direction of the recoil nuclei induced by DMp) with the respect to the crystal axes.

Crystals as anthracene, C14H10 and stilbene C14H12

• 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.

Larger anisotropic scintillators?

DIURNAL EFFECTSDIURNAL 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

Only for large cross sectionsInvestigation in DAMA/NaI-2 data (N.Cim. A112(1999)1541): 14962 kg d

Limits on halo fraction (ξ) vs σpfor SI case in the given model

Study on diurnal variation in the rate with suitable exposure and stability can allow to investigate:

high σp DMp component (with small ξ) in the dark halo and decouple ξ from σp

θ vs Sidereal timePLB275(1992)181

DIURNAL EFFECTSDIURNAL EFFECTS daily modulation on the sidereal time: due to the Earth rotation velocity contribution (wide range of DM candidates) Phys. Atom. Nucl. 72 (2009)2076

•This signature can allow a powerful decoupling from the models.

•However, considering the annual modulation amplitude observed in DAMA (in the (2-6) keVroughly 0.012 cpd/kg/keV) the expected diurnal modulation amplitude is 2×10-4 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.

Velocity of the detector in the galactic frame:

annual modulation term

diurnal modulation termangle beetwen the Earth axis and the DM flux

ds = 1 sideral day

td = phase depending on detector longitude

LNGS latitude

The ratio of the diurnal modulation amplitude over the annual modulation amplitude is a fully model-independent constant

Expected signal counting rate in a given k-th energy bin:

daily effect on the sidereal time: due to the channeling in case of DM candidates inducing nuclear recoils.

y

z

xy

z

x

xvearth ˆˆ ⋅

∆Rmax/R = 0.18 %Mass = 8 GeV

Percentage variation of the Rate in the sideral day (2-6 keV)

Maximum amplitude range withinthe sidereal day in (2-6 keV)If DM induces recoils, from DAMA results we expect roughly

1-5×10-4 cpd/kg/keV.

Mirror DM

• 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.

• 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 keVand/or in case of Mirror DM candidates.

Eur. Phys. J. C 53(2008)205

DIURNAL EFFECTSDIURNAL EFFECTS

Maximum amplitude range within the sidereal day in (2-6 keV)

blu:Cold Stream: a caustic halo model

• ρ0 = 0.84 GeV/cm3

• velocity distribution: stream with vx = 120 km/s, vy = 505 km/s, vz = 0 km/s

Caustic Halo model:

assumed here: vearth = 232 km/s

red:NFW model

• ρ0 = 0.3 GeV/cm3

• quasi-isotropic velocity distribution• v0 = 220 km/s, vesc = 650 km/s

Cyan: A0 halo model

• ρ0 = 0.3 GeV/cm3

• maxwellian velocity distribution• v0 = 220 km/s, vesc = 650 km/s

Isothermal model

green: halo model by Aquarius Project

NFW model

• velocity distribution: see picture • v0 ≈ 220 km/s

Aquarius model(Aq-A-2)

NEUTRINO PHYSICS with MultiTon NaI(Tl) set-upNEUTRINO PHYSICS with MultiTon NaI(Tl) set-up

• Solar neutrinos spectroscopy from νe-Na and νe-I real time interactions

• Investigation on ν oscillation from low energy, large activity artificial ν source (147Pm)

• Investigation on ν magnetic moment (artificial ν source)

• Search for new physics in neutrino interaction

Very low background MultiVery low background Multi--ton ton NaI(TlNaI(Tl) set) set--up can also up can also give interesting results on neutrinosgive interesting results on neutrinos

((AstropAstrop. Phys.4(1995)45,Astrop.Phys.8(1997)67,. Phys.4(1995)45,Astrop.Phys.8(1997)67,Nucl.Phys.B546(1999)19, Nucl.Phys.B546(1999)19, New Journal of Physics 3(2001)5.1)

...Last...

Crystal Crystal scintillators scintillators

& scintillation & scintillation techniquetechnique

Competitive and profitable choice for future experiments on rareCompetitive and profitable choice for future experiments on rare processesprocesses

Solid, well-known and evergreen detectors

widespread in many fields and

application

Continuous improvements in performance and radiopurity achieved with time passing

technology constantly in development

ConclusionsConclusions• ULB inorganic crystal scintillators are

powerful tools to investigate rare processes

• ULB NaI(Tl) has been succesfully used by DAMA/NaI and DAMA/LIBRA to investigate a particle Dark Matter component in the galactic halo exploiting the annual modulation signature

• Ultimate developments of low background techniques in crystal scintillators and related set-ups will further enlarge the frontier of investigation in rare processes

• ULB inorganic crystal scintillators are powerful tools to investigate rare processes

• ULB NaI(Tl) has been succesfully used by DAMA/NaI and DAMA/LIBRA to investigate a particle Dark Matter component in the galactic halo exploiting the annual modulation signature

• Ultimate developments of low background techniques in crystal scintillators and related set-ups will further enlarge the frontier of investigation in rare 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 fearYour favours nor your hate.W. Shakespeare "Machbeth" Act 1, scene 3