data analysis and background investigation in the edelweiss direct d ark m atter search
DESCRIPTION
Data analysis and background investigation in the EDELWEISS direct d ark m atter search. Earth moves through DM halo ρ DM = 0.3 GeV /cm 3. The corner of the dark we are looking at. . . Production. t. Annihilation. E R ~ 10 keV. q. q. ≈ 230 km/s. t. t. - PowerPoint PPT PresentationTRANSCRIPT
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
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
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
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
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)
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
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
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
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
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
EDELWEISS, IEKP, KIT13
Results expected for background free measurement
Benjamin Schmidt
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
EDELWEISS, IEKP, KIT15 Benjamin Schmidt