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KIT – Universität des Landes Baden-Württemberg undnationales Forschungszentrum in der Helmholtz-Gemeinschaft
Benjamin Schmidt, IEKP, KIT Campus North, EDELWEISS experiment
www.kit.edu
Photo by Böhringer Friedrich
Data analysis and background investigation in the EDELWEISS direct dark matter search
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EDELWEISS, IEKP, KIT2
The corner of the dark we are looking at
Benjamin Schmidt
Earth moves through DM halo
ρDM = 0.3 GeV/cm3
ER ~ 10 keV
<v> ≈ 230 km/s
M ~ 100 GeV/c2
q q
t
t
tScattering
Annihilation P
rodu
ctio
n
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EDELWEISS, IEKP, KIT3
WIMP() direct detection
ER ~ 10 keV, Count rate: < 1 evt / (kg·year)
Benjamin Schmidt
Heat
Ionization
Light
LXe, LAr
NaI, LXe, LAr
Ge, Si
CaWO4, BGO
Al2O3, LiF
1% energyfastest,no surface effects
10% energy
100% energyslowest,cryogenics
WIMP
Target
Ge, CS2, C3F8, He3
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EDELWEISS, IEKP, KIT4
The EDELWEISS experiment
Benjamin Schmidt
Polyethylene shield
Pb shield
Cryostat with bolometers
µ-veto
µ-n counter
Sensitivity Goal: s-n = a few·10-45 cm2 (< 10-3 evt/kg.d)
Cryogenic installation (18 mK) :Can host up to 40 kg of bolometer
Shieldings : Clean room + deradonized airActive muon veto (>98% coverage)PE shield 50 cm Lead shield 20 cm
Background studies :Radon detector down to few mBq/m3
thermal neutron monitoring (He3 det.)Muon-veto – bolometer coincidencesStrong AmBe source calibrationsStudy of muon induced neutrons (liquid scintillator 1 m3 neutron counter)
Shielding: ~ 4850 mwe m-flux (lab): ~ 5 m / m2 / day
µ
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EDELWEISS, IEKP, KIT5
Muon-induced background
Muons cause high energetic electron recoilsHowever, muon-induced secondaries and especially muon-induced neutrons constitute low energetic background that scatters off nuclei
Before veto: 0.008 (WIMPlike) evts/(kg·d)
Benjamin Schmidt
- All events- Fiducial events- Potential background for DM search
Muon induced bolometer events (1504 kg·d)
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EDELWEISS, IEKP, KIT6
Quantification of muon flux and muon veto efficiency – measurements and MC simulation
Muon veto efficiency1st method: (Measurement only) ε = (candidates in bolos/ evts in muon veto system)
ε ≥ 92,8% (90%CL) (34/34 observed)
2nd method: (Measurement + MC simulation) Determine trigger efficiency of each muon veto module; Simulate experiment with measured efficiency curves
ε = (97.7 ± 1.5) %Irreducible background flux 2·10-4 evts/(kg·d) (MPV)
Muon flux (horizontal area)Measurement + MC simulation: (5.4 ± 0.2 +0.5 -0.9) m/m2/d
Benjamin Schmidt
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EDELWEISS, IEKP, KIT9
Topography of muon-induced events
Benjamin Schmidt
Distance of muon track to detectors- All detected muons (scaled)- Muons with secondaries in
bolometers (coincidences)- Coincidences EBolo < 1 MeV- Coincidences EBolo > 1 MeV
Lead identified as main target for the production of muon-induced neutronsMuon induced events produce multiple hits – 2nd handle for rejectionBenefits from more detectors and new PE shield in EDW-3
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EDELWEISS, IEKP, KIT10 Benjamin Schmidt
A: +4 VB: 1.5V
C: 4 VD: +1.5V
Nuclear recoil event discrimination & Surface event rejection- principle
Bulk/Fiducial eventCharge collected on electrodes A&C
Surface eventCharge collected on electrodes A&B
NTD Phonon/Heat sensor = calorimetric measurement of total energy (T=18 mK, DT 0.2 mK/keV )
Al electrodes Ionization measurement ( sub-keV resolution)
Ionization yieldQ = EI/ERec nuclear recoils have ~1/3 Q of e-recoils
Event discrimination via simultaneous charge and phonon measurement
Fiducial volume
Count rate:
< 1 evt/kg/year!
WIMP100 GeV/c2
Scatt. WIMP Recoil nucleus ER ~10 keV
A A AB B
D DC C
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EDELWEISS, IEKP, KIT11
Outlook on data analysisTasks: 1st optimization of noise selection in optimal filter2nd adaptation of filtering techniques to new hardware
Benjamin Schmidt
Goal: improve stability and performance of optimal filterpotential gain in low mass WIMP region
Time domain
Frequency domain
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EDELWEISS, IEKP, KIT12
Tasks: Investigation of potential of new hardware
Currently a new DAQ-system is being developed at KIT(talk by B. Siebenborn)
Features fast 40 MHz read-out of ionization channelsTime-resolved measurements of charge propagation Better understanding of detectors plus new possibilities for surface event discrimination
Benjamin Schmidt
Fiducial Volume> 600 g
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EDELWEISS, IEKP, KIT13
Results expected for background free measurement
Benjamin Schmidt
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EDELWEISS, IEKP, KIT14
While I have got the word:
The hike todayThe easy way - just follow me13.30 o’clock from the castle
There are also GPS-data and descriptions availablehttp://www.outdooractive.com/de/wanderung/nordschwarzwald/durch-das-wildromantische-monbachtal/1398559/download.html#axzz2COBW0Gc2
Benjamin Schmidt
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EDELWEISS, IEKP, KIT15 Benjamin Schmidt