Physics at Extreme Energies, Hanoi, July 2000 Dark Matter Search in the EDELWEISS expt G. Chardin DAPNIA/SPP, CEA-Saclay.

Physics at Extreme Energies, Hanoi, July 2000Physics at Extreme Energies, Hanoi, July 2000

Dark Matter SearchDark Matter Searchin the EDELWEISS exptin the EDELWEISS expt

G. ChardinG. Chardin

DAPNIA/SPP, CEA-SaclayDAPNIA/SPP, CEA-Saclay


EDELWEISS CollaborationEDELWEISS Collaboration

CEA-Saclay DAPNIACEA-Saclay DAPNIA: G. Chardin, M. Gros,: G. Chardin, M. Gros,A. Juillard, A. de Lesquen, M. Loidl, J. Mallet, A. Juillard, A. de Lesquen, M. Loidl, J. Mallet, L. Miramonti, L. Mosca, X-F. NavickL. Miramonti, L. Mosca, X-F. Navick

CEA-Saclay DRECAMCEA-Saclay DRECAM: M. Chapellier, P. Pari: M. Chapellier, P. Pari

CRTBT GrenobleCRTBT Grenoble: A. Benoit, M. Caussignac: A. Benoit, M. Caussignac

CSNSM OrsayCSNSM Orsay: L. Bergé, A. Broniatowski, : L. Bergé, A. Broniatowski, L. Dumoulin, A. Juilliard, S. Marnieros,L. Dumoulin, A. Juilliard, S. Marnieros,N. MirabolfathiN. Mirabolfathi

IAP ParisIAP Paris: C. Goldbach, G. Nollez: C. Goldbach, G. Nollez

IPN LyonIPN Lyon: B. Chambon, M. De Jesus, D. Drain, : B. Chambon, M. De Jesus, D. Drain, J. Gascon, J-P. Hadjout, O. Martineau,J. Gascon, J-P. Hadjout, O. Martineau,C. Pastor, E. Simon, M. SternC. Pastor, E. Simon, M. Stern

Fréjus Underground LabFréjus Underground Lab: Ph. Charvin: Ph. Charvin


EDELWEISSEDELWEISSDark Matter SearchDark Matter Search

IntroductionIntroduction Limitations of present experimentsLimitations of present experiments Cryogenic double detection detectorsCryogenic double detection detectors First 70 g germanium detectors: First 70 g germanium detectors:

discrimination performancesdiscrimination performances Anomalous NaI eventsAnomalous NaI events Second generation 70 g detectorsSecond generation 70 g detectors Present stage: 3 x 320 g Ge detectorsPresent stage: 3 x 320 g Ge detectors First results and expected sensitivityFirst results and expected sensitivity The EDELWEISS-II experimentThe EDELWEISS-II experiment Perspectives and conclusionsPerspectives and conclusions


WIMPs direct detection:WIMPs direct detection:(some) conventional and cryogenic (some) conventional and cryogenic experimentsexperiments

ELEGANT,ELEGANT, LiF LiF

CDMSCDMSEDELWEISSEDELWEISS

CRESST, HDMS,CRESST, HDMS,DAMADAMAGran SassoGran Sasso

AMANDAAMANDA (indirect)(indirect)

ANTARESANTARES(indirect)(indirect)

UKDMCUKDMC

EDELWEISS: Fréjus underground labEDELWEISS: Fréjus underground lab

• • CRESST AlCRESST Al22OO33(Münich/Oxford) @ Gran Sasso(Münich/Oxford) @ Gran Sasso

• • EDELWEISSEDELWEISS (Ge @ (Ge @ FréjusFréjus))• • ROSEBUD ROSEBUD @@ Canfranc Canfranc• Milano/Genova/Napoli/ (Te0• Milano/Genova/Napoli/ (Te022) @ Gran Sasso) @ Gran Sasso

• • CDMS (Ge and Si, Berkeley/Stanford)CDMS (Ge and Si, Berkeley/Stanford)• • DAMA (NaI, Xe @ Gran Sasso)DAMA (NaI, Xe @ Gran Sasso)• UKDMC (NaI @ Boulby Mine)• UKDMC (NaI @ Boulby Mine)• • ELEGANT, LiF @JapanELEGANT, LiF @Japan

ROSEBUDROSEBUD


The Fréjus Underground The Fréjus Underground LaboratoryLaboratory

• • Muon flux ≈ 4 muons/mMuon flux ≈ 4 muons/m22/day/day• • Neutron flux (mainly from rock)Neutron flux (mainly from rock)

≈ 4 10≈ 4 10-6-6 s s-1-1 cm cm-2-2


EDELWEISSEDELWEISSWIMP searchWIMP search

Measure charge and heat signal Measure charge and heat signal to separate :to separate :• electron recoils electron recoils

((background)background)• nuclear recoils (neutrons, nuclear recoils (neutrons,

WIMPs…)WIMPs…)

0

20

40

60

80

100

0 20 40 60 80 100

Phonon amplitude (keV e.e.)

Charge amplitude (keV e.e.)

EDELWEISS Collaboration

0

20

40

60

80

100

0 20 40 60 80 100

Phonon amplitude (keV e.e.)


EDELWEISS Collaboration


EDELWEISSEDELWEISSWIMP searchWIMP search

Physics data takings:Physics data takings:NotNot two, two, butbut four four populations observed populations observed(nuclear and electron recoils, volume (nuclear and electron recoils, volume and and surfacesurface events) events)

0

20

40

60

80

100

0 10 20 30 40 50

Recoil energy (keV)


Nuclearsurfaceevents

Nuclearvolumeevents Electron

surfaceevents

Electronvolumeevents

EDELWEISSCOLLABORATION0

20

40

60

80

100

0 10 20 30 40 50

Recoil energy (keV)


Nuclearsurfaceevents

Nuclearvolumeevents Electron

surfaceevents

Electronvolumeevents

EDELWEISSCOLLABORATION


Unexpected events…Unexpected events…

Anomalous events in UKDMC and Anomalous events in UKDMC and Saclay NaI experiments (not Saclay NaI experiments (not reported by DAMA): events almost reported by DAMA): events almost like nuclear recoils but faster…like nuclear recoils but faster…

EDELWEISS example: not EDELWEISS example: not twotwo, but , but fourfour categories of events categories of events

Surface nuclear recoils: A. Benoit et Surface nuclear recoils: A. Benoit et al., Phys. Lett. B 479 (2000) 8al., Phys. Lett. B 479 (2000) 8

Surface events probably represent Surface events probably represent the main limitation of NaI, classical the main limitation of NaI, classical germanium (e.g. HDMS, GENINO) germanium (e.g. HDMS, GENINO) and cryogenic germanium and cryogenic germanium experimentsexperiments


Anomalous events in NaI Anomalous events in NaI experimentsexperiments

Tails on the Tails on the time distribution time distribution of NaI events: of NaI events: Events faster Events faster than nuclear than nuclear recoilsrecoils

Rate:Rate:few 10few 10-1-1 - 10 - 10-2-2 evts/kg/keV/dayevts/kg/keV/day

Total number < Total number < Nb of alpha Nb of alpha eventsevents

Smith and Spooner,Smith and Spooner,Phys. World Jan. 2000Phys. World Jan. 2000


Low energyLow energysurface nuclear recoilssurface nuclear recoils

Consider for example the Consider for example the -decay -decay of of 210210Po Po 206206Pb + Pb + due to a due to a pollution at the detector surface:pollution at the detector surface:

For a total released energy of 5 For a total released energy of 5 MeV, ≈4.9 MeV will be carried MeV, ≈4.9 MeV will be carried away by theaway by the particle and ≈100 particle and ≈100 keV by the keV by the 206206Pb nucleus.Pb nucleus.

-particlePo210Pb206 -particlePo210Pb206


Anomalous NaI events: Anomalous NaI events: surface nuclear recoils ?surface nuclear recoils ?

Surface nuclear recoils will give events Surface nuclear recoils will give events in in the 5-10 keV rangethe 5-10 keV range(since quenching factor <0.1)(since quenching factor <0.1)

Heavy nuclei at low energy and on Heavy nuclei at low energy and on surface: scintillation decay times surface: scintillation decay times expected expected to be fasterto be faster than nuclear Na or I recoils, or than nuclear Na or I recoils, or alphasalphas(see UKDMC and Saclay publications)(see UKDMC and Saclay publications)

Note: energy observed in detector will Note: energy observed in detector will depend strongly on state of detector depend strongly on state of detector surface (very flat surface : apparent energy surface (very flat surface : apparent energy 5-10 keV, rougher surface : 5-10 keV, rougher surface : energy loss energy loss in addition possible)in addition possible)

Event rate appears Event rate appears compatible with compatible with event rateevent rate (up to trigger effects, should be (up to trigger effects, should be the same as surface alphas)the same as surface alphas)


Anomalous events:Anomalous events:ConsequencesConsequences

Discrimination analysis: Discrimination analysis: statistical statistical discriminationdiscrimination (distributions overlapping) (distributions overlapping) requires that requires that all populations be identifiedall populations be identified(fit with 2 degrees of freedom ≠ 4 d.o.f)(fit with 2 degrees of freedom ≠ 4 d.o.f)

Necessary to include Necessary to include additional degrees additional degrees of freedomof freedom of surface electron recoils (cf. of surface electron recoils (cf. Saclay) and surface nuclear recoils (for Saclay) and surface nuclear recoils (for NaI + all discrimination expts)NaI + all discrimination expts)

Expected to play a significant role in spin-Expected to play a significant role in spin-dependent analysis (marginally for dependent analysis (marginally for coherent coupling) (factor ≈10)coherent coupling) (factor ≈10)

Note: even if population is not seen, it Note: even if population is not seen, it should be included in the fit (if surface should be included in the fit (if surface state is excellent, visible energy will be 5-state is excellent, visible energy will be 5-10 keV in NaI crystals)10 keV in NaI crystals)


Anomalous events:Anomalous events:Consequences (ff)Consequences (ff)

Important to study in detail Important to study in detail surface surface eventsevents for for chargecharge detectors, detectors,and also for and also for scintillationscintillation detectors detectors

Further study to confirm our hypothesis: Further study to confirm our hypothesis: analysis of coincident data taken with analysis of coincident data taken with Ge-4 and Ge-5 detectors (but saturation Ge-4 and Ge-5 detectors (but saturation and non linearity of heat channel)and non linearity of heat channel)

Hypothesis can be tested on a NaI Hypothesis can be tested on a NaI crystal by using an implanted source (Po crystal by using an implanted source (Po or Rn, e.g., cf. Milano groupor Rn, e.g., cf. Milano group

Events present in Events present in DAMADAMA ? (same ? (same crystals as Saclay), discrimination crystals as Saclay), discrimination factors taking into account additional factors taking into account additional population ?population ?


The DAMA claimThe DAMA claim

Detected not by direct Detected not by direct observation, but by observation, but by searching for an annual searching for an annual modulation effect (≈10modulation effect (≈1055 events if correct)events if correct)

0

0,02

0,04

0,06

0,08

0,1

0,12

0 20 40 60 80 100 120 140

Event rate in Germanium detectorassuming DAMA signal really exists

Event rate (/keV/kg/day)

Recoil energy (keV)

Germanium detector

σχ-p

=7 10x -6 pb

Mχ≈50GeV

≈5 Effect of keV charge threshold

Raw spectrum

20-100 :keV≈1.6 / /event kg day

0

0,02

0,04

0,06

0,08

0,1

0,12

0 20 40 60 80 100 120 140

Event rate in Germanium detectorassuming DAMA signal really exists

Event rate (/keV/kg/day)

Recoil energy (keV)

Germanium detector

σχ-p

=7 10x -6 pb

Mχ≈50GeV

≈5 Effect of keV charge threshold

Raw spectrum

20-100 :keV≈1.6 / /event kg day


2nd generation 70g 2nd generation 70g germanium bolometersgermanium bolometers

Improved radioactive environmentImproved radioactive environment Close roman lead shieldClose roman lead shield Removable paraffin shielding (30 cm thick)Removable paraffin shielding (30 cm thick) Acoustic isolation improvedAcoustic isolation improved Nitrogen flushing against radonNitrogen flushing against radon New implantation schemes for the electrodesNew implantation schemes for the electrodes

0

0.5

1

1.5

2

0 50 100 150 200

Second generation 70g Germanium detectorRadioactive background before rejection ≈ 2evt/kg/keV/day

(approx. 1.04 kg x day)

Quenching factor(normalized to 1 for electron recoils)

Recoil energy (keV)

0

0.5

1

1.5

2

0 50 100 150 200

Second generation 70g Germanium detectorRadioactive background before rejection ≈ 2evt/kg/keV/day

(approx. 1.04 kg x day)

Quenching factor(normalized to 1 for electron recoils)

Recoil energy (keV)


330 g Ge detectors of the 330 g Ge detectors of the "1 kg" stage of EDELWEISS-I"1 kg" stage of EDELWEISS-I


320 g Ge detectors of the 320 g Ge detectors of the "1 kg" stage of EDELWEISS-I"1 kg" stage of EDELWEISS-I

Three 320 g Ge detectorsThree 320 g Ge detectors Close spacing, guard ring for Close spacing, guard ring for

middle detectormiddle detector Improved radioactive Improved radioactive

environmentenvironment


"1 kg" stage of "1 kg" stage of EDELWEISS-I: first resultsEDELWEISS-I: first results

Very preliminaryVery preliminary data from first 320 g detector data from first 320 g detector

Still a factor ≈ 5 from CDMS and DAMA Still a factor ≈ 5 from CDMS and DAMA benchmarks, but resolution can be significantly benchmarks, but resolution can be significantly improved and improved and new detector with guard ring + new detector with guard ring + germanium protection starting to be operatedgermanium protection starting to be operated

0

50

100

150

0 50 100 150

Preliminary data taking with 320 g Ge detectorRun 1113: ≈ 0.65 kg x day

Phonon energy (keV)

Charge Energy (keV)

Before rejection: ≈ 4 evt/kg/keV/day

After rejection (prelim.): few 10 -2 evt/kg/keV/day

0

50

100

150

0 50 100 150

Preliminary data taking with 320 g Ge detectorRun 1113: ≈ 0.65 kg x day

Phonon energy (keV)

Charge Energy (keV)

Before rejection: ≈ 4 evt/kg/keV/day

After rejection (prelim.): few 10 -2 evt/kg/keV/day


Reaching SUSY modelsReaching SUSY models

EDELWEISS 2000expected sensitivity

WIMP Mass [GeV]

WIMP-Nucleon Cross-Section [cm2]

EDELWEISS 2000expected sensitivity

WIMP Mass [GeV]

WIMP-Nucleon Cross-Section [cm2]


EDELWEISS:EDELWEISS:R&D to get rid of surface eventsR&D to get rid of surface events

Discrimination performances of charge Discrimination performances of charge + heat detectors are excellent, + heat detectors are excellent, but but surface events are uncomfortably close surface events are uncomfortably close to nuclear recoil bandto nuclear recoil band

To remove surface events:To remove surface events:• record record risetime structure of charge risetime structure of charge

signalsignal (A. Broniatowski et al.) (A. Broniatowski et al.)• detect detect out-of-equilibrium phonons out-of-equilibrium phonons

and fast vs. slow component ratioand fast vs. slow component ratio• lower charge energy thresholdlower charge energy threshold and and

improve energy resolutionimprove energy resolution(AsGa FETs, Single Electron (AsGa FETs, Single Electron Transistor)Transistor)


Remove surface events (ff)Remove surface events (ff)

Large NbSi Large NbSi film sensors film sensors efficiently efficiently collect out-of-collect out-of-equilibrium equilibrium phonons phonons (« fast » (« fast » component)component)

Fast/slow Fast/slow component component ratio depends ratio depends on location of on location of energy energy depositiondeposition

Sensor 1

Sensor 2

Radioactive source


Remove surface events (ff)Remove surface events (ff)

Record risetime structure of charge Record risetime structure of charge signal (A. Broniatowski et al. LTD8 conf. signal (A. Broniatowski et al. LTD8 conf. proc.)proc.)

Cut on risetimeCut on risetimeis able to removeis able to removeelectron eventselectron eventsat 60 keVat 60 keV

Pb: reach thePb: reach the<≈10 keV level<≈10 keV level

Insidecrystal

Charge signal (10 C)-14

Charge signal (10 C)-14

Electrodeevent

0 0.5 1.0 1.5 2.0 µs 0 0.5 1.0 1.5 2.0 µs


Decrease charge threshold Decrease charge threshold using theusing theSingle Electron TransistorSingle Electron Transistor

Charge manipulation in the Charge manipulation in the quantum regimequantum regime

Ultra small capacitances now Ultra small capacitances now achievable ≈ 1 fF (10achievable ≈ 1 fF (10-15-15 F) F)

Coulomb blockade: when 1 Coulomb blockade: when 1 electron present, other electrons electron present, other electrons must wait outsidemust wait outside

3-4 orders of magnitude increase 3-4 orders of magnitude increase in charge sensitivity over best in charge sensitivity over best FET-based devices if FET-based devices if capacitance is adapted capacitance is adapted

Dual of the SQUID systemDual of the SQUID system


An SET-basedAn SET-basedSi photodetectorSi photodetector

Cleland et al. (Cleland et al. (Appl. Phys. Lett. 61 Appl. Phys. Lett. 61 (1992) 2820(1992) 2820): proof of principle, ): proof of principle, coupling of a Si detector to a coupling of a Si detector to a Single Electron Transistor circuitSingle Electron Transistor circuit


Extending the bandwidth of Extending the bandwidth of the SET for charge detectionthe SET for charge detection

Idea: move to high-Idea: move to high-frequenciesfrequencies

Ex: couple the SET to Ex: couple the SET to a GHz resonant a GHz resonant circuit and measure circuit and measure damping (Schoelkopf damping (Schoelkopf et al. Science 1998)et al. Science 1998)

Fantastic sensitivity: still-unoptimized Fantastic sensitivity: still-unoptimized device: ≈ 10device: ≈ 10-5-5 e/√Hz e/√Hz

Sensitive enough to feel a single particleSensitive enough to feel a single particle Problem: capacitive coupling is difficultProblem: capacitive coupling is difficult EDELWEISS: realize a prototype with C EDELWEISS: realize a prototype with C

≈ 2 pF and ≈ 500 eV charge threshold≈ 2 pF and ≈ 500 eV charge threshold


EDELWEISS-II shieldingEDELWEISS-II shielding

• • Efficient protection against neutronEfficient protection against neutronand gamma-ray backgroundsand gamma-ray backgrounds• • Designed to improve by > 2 orders ofDesigned to improve by > 2 orders ofmagnitude the best present performancesmagnitude the best present performances


InnovativeInnovativereversed cryostat (100 l)reversed cryostat (100 l)

• • Large Large volume (100 l)volume (100 l)• • Efficient Efficient geometrygeometry• • Innovative Innovative cryogenic cryogenic solutions solutions (pulsetubes, (pulsetubes, compact compact cryogenic cryogenic system…)system…)• • 10 mK base10 mK basetemperaturetemperature


ConclusionsConclusions

EDELWEISS Dark Matter Search:EDELWEISS Dark Matter Search:now entering the allowed region ofnow entering the allowed region ofSUSY modelsSUSY models

The present "1 kg" stage should be able The present "1 kg" stage should be able to test the whole DAMA regionto test the whole DAMA region

Detector developments are pursued to:Detector developments are pursued to:• get rid of surface eventsget rid of surface events• lower charge energy thresholdlower charge energy threshold• apply developments to other physics apply developments to other physics

applications: coherent applications: coherent scattering, solar scattering, solar neutrinos, mass of antiproton…neutrinos, mass of antiproton…

Testing most of SUSY parameter space Testing most of SUSY parameter space will require > 50-100 kg stagewill require > 50-100 kg stage

EDELWEISS is exploring with CRESST EDELWEISS is exploring with CRESST the best strategy for a cryogenic the best strategy for a cryogenic experiment at the 100 kg scale.experiment at the 100 kg scale.

Physics at Extreme Energies, Hanoi, July 2000 Dark Matter Search in the EDELWEISS expt G. Chardin DAPNIA/SPP, CEA-Saclay.

Documents