DAMA/R&DDAMA/LXe

DAMA/Ge

DAMA/NaI DAMA/LIBRA

R. Cerulli INFN-LNGS

Nuclear Physics in Astrophysics-II Debrecen, Hungary, May 2005

XELIDON(1989-92)5th Nat.Sci.Com.INFN

1990 DAMA/LXe, pure liquid scintillator (direct collection of UV light, no other material apart from xenon present in the sensitive volume, assuring high radiopurity level, high

light response and PSD capability, no liquid-gas interface between liquid and PMTs)

low background developments and applications to dark matter

investigation (since N.Cim.A103(1990)767)

Many scintillator prototypesand R&D using natural Xe realised

• Dark Matter investigation• investigation on ββ decay

processes in 136Xe and 134Xe• charge-non-conserving processes• nucleon, di-nucleon and tri-

nucleon decay into invisible channels

• Significant upgrade of the set-up atthe end of 1995;

• deeply modified in 2000;• last upgrade in 2003 on DAQ and refrigeration water system (chiller installed)

Kr-free enriched in129Xe at 99.5%

Kr-free enriched in136Xe at 68.8%

A brief history…

DAMA/LXeDAMA/LXe setset--up at Gran Sassoup at Gran SassoNIM A482(2002)728Main parts of the set-up:

• the inner vessel (internal volume ≈ 2 liters) where the xenon undergoes the transition between gaseous and liquid phase;

• the external vessel where the insulation vacuum is made and where three photomultipliers are located and shielded

• the passive shield;• the cryogenic system constituted of a v/f/p/r system for the

xenon. Used gases:• Kr-free enriched in 129Xe at 99.5%• Kr-free enriched in 136Xe at 68.8%

The inner vessel

Some view of the set-up during installation

The innerThe inner--vesselvessel• OFHC low-radioactivity copper; to

optimize light collection inner sensitive volume excavated smoothly in a quasi-spherical shape. Volume ≈ 2 l, 6.5 kg of LXe

• No wave-shifter, no diffuser/reflector, direct light collection by three PMTs with MgF2windows. No liquid-gas interface between liquid and PMTs.

• Three CONFLAT flanges assure the connection with the optical windows 10 cm in diameter made of culturedcrystal quartz (transm. ≥ 80% to UV of LXe pure scintillator).

• Initial vacuum before filling not worse than 10-6 mbar

The external vesselThe external vessel• 316 stainless steel cylinder (~ 100 l)

with various feedthroughs and flanges in order to work on PMTs, cold head, sensors, etc.

• Insulation vacuum: ∼10-3 mbar.

• Three 3.5” in diameter flying leads PMTs with MgF2 windows and q.e.ranging between 18% and 32% @ 175 nm with a flat behaviour depending on the PMT.

• Flying leads directly connected to voltage dividers + low background materials used.

• Filled with low bckg Cu brick as much as possible.

Simplified lateral view of the external vessel and the shield

Purification:• A cold trap at 190 K purifies Xe from possible Rn, H2O and other impurities that condense at this temperature.

• Home-made and mono-Torr getters (previously activated at 400 oC):

R. Bernabei et al., NIM A482 (2002) 728

Stability on T~0.1 oC (example over 1 month) Visualization of Visualization of

monitoring system on PCmonitoring system on PC

MonitoringMonitoring systemsystem

σ ~220 keV @ 2614 keVσ ~70 keV @ 662 keV

Example of CalibrationsExample of Calibrations137Cs external source

Response to a γ(2.614 MeV) of

208Tl

Placed outside the external vessel near the flange, which closes the entrance for the removable tomback.

NIM A482 (2002) 728PLB 546 (2002) 23

109Cd internal source (γ’s of 22keV and 88 keV)

109Cd source is sealed in a small stainless steel capsule with a thin window (190 µm) suitable to work in the operative conditions of our set-up (UHV, low temperature and high pressure of Xe).

... also study on internal alphas(see NIM A482 (2002) 728)

DAMA/LXe DAMA/LXe results on rare processesresults on rare processes

• Electron decay into invible channelsτ > 1.6×1023 y at 68% C.L Astrop.Phys5(1996)217

• Nuclear level excitation of 129Xe during CNC processesτ > 1.1×1024 y at 90% C.L PLB465(1999)315

• Nucleon and di-nucleon decay into invisible channels in 129Xe PLB493(2000)12τ>1.9×1024 y 90% C.L. (p→invisible channel), τ>5.5×1023 y 90% C.L. (pp→invisible channel), τ>1.2×1025 y 90% C.L. (nn→invisible channel)

• Electron decay e- → νeγ PRD61(2000)117301τ > 2.0×1026y at 90% C.L.

• 2β decay in 136Xe T1/2 > 7.0×1023y (90% CL) Xenon01• 2β decay in 134Xe PLB527(2002)182• Improved results on 2β in 134Xe,136Xe PLB546(2002)23• CNC decay 136Xe → 136Cs τ > 1.3×1023y at 90% C.L.

• Nucleon, di-nucleon and tri-nucleon decay into invisible

channels in 136Xe

... other rare processes

Cold DARK MATTER particle (CDMp) investigation ...• Limits on recoils investigating the CDMp-129Xe elastic scattering by means of Pulse Shape

Discrimination PLB436(1998)379• Limits on CDMp-129Xe inelastic scattering PLB387(1996)222, NJP2(2000)15.1• Neutron calibration PLB436(1998)379, EPJdirectC11(2001)1• 129Xe vs 136Xe by using PSD → comparing SD vs SI signal to increase the sensitivity on the SD

component foreseen/in progress

NIMA482(2002)728

INFN/EXP-08/03 + proceed.+ in progress

INFN/EXP-08/03 + proceed.+ in progress

A) Limits on recoils investigating the CDMp-129Xe elastic scattering by means of Pulse Shape Discrimination

measured upper limits on recoils

total rate

LXeLXe: Dark Matter search: Dark Matter searchB) Limits on CDMp-129Xe inelastic scattering

Search for characteristic peak (39.58 keV) in the measured energy spectrum as a result of emission of successive de-excitation γ from the excited nuclear states.PLB436 (1998)379

C) Neutron calibration

DAMA 2000NJP2 (2000) 15.1

DAMA ‘ 96PLB387 (1996) 222for a given model framework

σ I (v) =µ 2

πMNN * | M | N

21 −

vthr2

v2= σ I

as 1−vthr2

v2

Ratio between the response of a recoil nucleus and of an electron with the same kinetic energy; measurements:97/98 - Am-B source and the 14 MeV neutron

generator at ENEA-Frascati.2001 - Further measurements by using the 2.5 MeV

neutron generator at ENEA-Frascati

14 MeV neutron generator PLB436(1998)379

Am-B neutron sourcePLB436 (1998)379

2.5 MeV neutron generator EPJdirect C11 (2001) 1

Overall averaged value: 0.46 ± 0.10

Some DAMA/LXe resultsSome DAMA/LXe results on rare processes with on rare processes with 129129XeXe1) Electron instabilities

PRD61(2000)117301Astrop.Phys5(1996)217 PLB465(1999)315

Electron decay into a neutrino and a γ quantum

Electron disappearance with excitation of low energy nuclear levels of 129Xe

Search for electron decay in the channel:-e → νeγ

Search for γ with ≈ 255 keV which could follow the possible decay of any electron in the LXe scintillator and in its surroundings

τe > 2.0 1026 y

-Search for electron decay in the channel:

eSearch for the nuclear level excitationof 129Xe during CNC processes:

129Xe + e- → 129Xe* + νeτe > 3.7 1024 y

Search for the nuclear level excitation→ νeγ

Search for γ with ≈ 255 keV which could follow the possible decay of any electron in the LXe scintillator and in its surroundings

τe > 2.0 1026 y

of 129Xe during CNC processes:129Xe + e- → 129Xe* + νe

τe > 3.7 1024 y

2) Nucleon, di-nucleon instabilitiesDisappearance or decay into invisible channels PLB493(2000)12

• Search for the radioactive daughter nuclei created after the nucleon or di-nucleon decay or disappearance in the parent nuclei

• If T1/2 of daughter nucleus is ~1s, its decay can be separated in time from the prompt products if any of them are observable in the detector

24τp → invisible channel > 1.9 × 10 y 90% C.L.23τpp → invisible channel > 5.5 × 10 y 90% C.L.25τnn → invisible channel > 1.2 × 10 y 90% C.L.

• Search for the radioactive daughter nuclei created after the nucleon or di-nucleon decay or disappearance in the parent nuclei

• If T1/2 of daughter nucleus is ~1s, its decay can be separated in time from the prompt products if any of them are observable in the detector

τp → invisible channel > 1.9 × 1024y 90% C.L.τpp → invisible channel > 5.5 × 1023y 90% C.L.τnn → invisible channel > 1.2 × 1025y 90% C.L.

In the following I will focus my attention on ββ decay in 136Xe and on the new results obtained on some rare processes

Investigation onInvestigation on ββββ decaydecay inin 136136XeXe and inand in 134134XeXeTotal Statistics: 8823.54 h → 68.8% in 136Xe (4.5 kg×y 136Xe), 17.1% in 134Xe (1.1 kg×y 134Xe)

PLB546(2002)23

136Xe134Xe

Qββ = 830 keV

Qββ = 2467 keV

residuals

134Xe 136Xe

Joint analysis of the 0νββ decay mode in 134Xeand 136Xe carried out as suggested by F.Simkovic et al., hep-ph/0204278:1) backgr estimated excluding the energy regions of 0νββ(0+→0+) decays in 134Xe and 136Xe.2) residuals

Analysing the single processes:134Xe 0νββ(0+→0+): T1/2 > 5.8 × 1022 y (90%CL)136Xe 0νββ(0+→0+): T1/2 > 1.2 × 1024 y (90%CL)

Exclusion plot in the positive sector of plane versus ηN obtained from the model of F. Simkovic et al.,

68% CL

90% CL68% CL

90% CL

Fit on residuals with linear combination of the expected signal from 0νββ(0+→0+) processes in 134Xe and 136Xe.

PLB546(2002)23

The limit value on is comparable with those obtained - depending on the model [1-4] -from the result on the 0νββ(0+→0+) decay mode of 136Xe alone, in fact they range from 1.1and 2.9 eV (90%C.L.).

[1] J.Suhonen et al., Nucl. Phys. A535 (1991) 91; [2] J.Engel et al., Phys. Rev. C37 (1988) 731[3] T. Tomoda, Rep. Prog. Phys. 54 (1991) 53 [4] K. Muto et al., Z. Phys. A334 (1989b) 187

modelization and

Other limits (90%CL) :136Xe 0νΜββ(0+→0+): T1/2 >5.0 × 1023 y 136Xe 2νββ(0+→0+): T1/2 > 1.0 × 1022 y Without any backgr136Xe 2ν ββ(0+→2+): T1/2 > 9.4 × 1021 ysubtraction

NewNew results on possible results on possible CNC CNC decay of decay of 136136Xe into Xe into 136136CsCs

τCNC > 1.3·1023 y (90%C.L.)

136Xe → 136Cs + massless uncharged particle + νe136Xe → 136Cs + massless uncharged particle + νe

Total Statistics 8823.54 h

Energy spectrum

LNGS-EXP 08/03+ various proceedings+ in progress

Response function simulation for 136Cs decay in DAMA/LXe detector

First experimental limit for this CNC decay cahnnel

β- decay without electron emission

Limit obtained fitting the experimental spectrum considering a bckg model + response finction for the process:

NewNew results on possibleresults on possible nucleon, dinucleon, di--nucleon and nucleon and tritri--nucleon decay into invisible channels in nucleon decay into invisible channels in 136136XeXe

•Search for the radioactive daughter nuclei created after N, NN, NNN decay or disappearance in the parent nuclei

•If T1/2 of daughter nucleus is ~1s, its decay can be separated in time from the prompt products if any of them are observable in the detector

•Search for the radioactive daughter nuclei created after N, NN, NNN decay or disappearance in the parent nuclei

•If T1/2 of daughter nucleus is ~1s, its decay can be separated in time from the prompt products if any of them are observable in the detector

decay dau. nucl. decay modes

* 135Cs is unstable with T1/2 = 2.3 106 yr** reported here only the main part of the chain

Processes of N, NN, NNN decays in 136Xe

Branching ratio ~ 1Efficiency ~ 1Real Time experiment

LNGS-EXP 08/03 + various proceedings + in progress

T1/2 of decays in the table range from 2.5 m (133Sb) to5.2 days (133Xe):

⇒ decay chains in equilibrium;

⇒ subsequent decays time resolved

Data analysis: an exampleThe processes: pp → can. inv.: 136Xe → 134Te → 134I → 134Xepp β

- β-

Calculated response function of the 2 decays

τ=1.9 1024 y

τ=2.1 1023 y

residuals

Data analysis: an example

pp decay produces 2 events in the detector ⇒ higher detection efficiency

136Xe: 4.5 kg×yr

Limit obtained fitting the experimental spectrum considering a bckg model + response finction for the process:

τ pp> 1.9 ·1024 yr (90% C.L.)

Note: in case of no peak expected, the used analysis procedure requires that the signal may not exceed the experimental spectrum

τn > 3.3 ·1023 yr τp > 4.5 ·1023 yr

τppp > 3.6 ·1022 yrτnnp > 1.4 ·1022 yr τnpp > 2.7 ·1022 yr

τnp > 3.2 ·1023 yrResults on other nucleon, diResults on other nucleon, di--nucleon and trinucleon and tri--nucleon nucleon decay into invisible channels (decay into invisible channels (90%C.L.)90%C.L.)

Energy (keV) Energy (keV) Energy (keV)

Energy (keV) Energy (keV) Energy (keV)

Cou

nts/

50ke

V

Cou

nts/

50ke

V

Cou

nts/

50ke

V

Cou

nts/

50ke

V

Cou

nts/

50ke

V

Cou

nts/

50ke

V

neutron decay in 136Xe proton decay in 136Xe

neut.-prot. decay in 136Xe

dineut-prot. decay in 136Xe diprot.-neut. decay in 136Xe triproton decay in 136Xe

• This method has allowed to obtain competitive limits with a small detector respect to other high mass apparata whose studyied similar processes

• This limits are valid for all invisible decay channels• The limits for NNN decays has been obtained for the first time

ConclusionsConclusions

•• DAMA/LXe operative since time in various DAMA/LXe operative since time in various configurations;configurations;

•• Results obtained on several topics both with Results obtained on several topics both with 129129Xe Xe and and 136136Xe;Xe;

•• Further data taking foreseenFurther data taking foreseen