KIT – Universität des Landes Baden-Württemberg und nationales Forschungszentrum in der Helmholtz-Gemeinschaft Benjamin Schmidt, IEKP, KIT Campus North, EDELWEISS experiment Photo by Böhringer Friedrich Data analysis and background investigation in the EDELWEISS direct dark matter search

EDELWEISS, IEKP, KIT 2 The corner of the dark we are looking at Benjamin Schmidt Earth moves through DM halo ρ DM = 0.3 GeV/cm 3 E R ~ 10 keV ≈ 230 km/s M ~ 100 GeV/c 2 qq   t t t Scattering Annihilation Production

EDELWEISS, IEKP, KIT 3 WIMP(  ) direct detection E R ~ 10 keV, Count rate: < 1 evt / (kg·year) Benjamin Schmidt Heat Ionization Light LXe, LAr NaI, LXe, LAr Ge, Si CaWO 4, BGO Al 2 O 3, LiF 1% energy fastest, no surface effects 10% energy 100% energy slowest, cryogenics WIMP Target Ge, CS 2, C 3 F 8, He 3

EDELWEISS, IEKP, KIT 4 The EDELWEISS experiment Benjamin Schmidt Polyethylene shield Pb shield Cryostat with bolometers µ-veto µ-n counter  Sensitivity Goal:   -n = a few· cm 2 (< evt/kg.d) Cryogenic installation (18 mK) : Can host up to 40 kg of bolometer Shieldings : Clean room + deradonized air Active muon veto (>98% coverage) PE shield 50 cm Lead shield 20 cm Background studies : Radon detector down to few mBq/m 3 thermal neutron monitoring (He 3 det.) Muon-veto – bolometer coincidences Strong AmBe source calibrations Study of muon induced neutrons (liquid scintillator 1 m 3 neutron counter) Shielding: ~ 4850 mwe  -flux (lab): ~ 5  / m 2 / day µ

EDELWEISS, IEKP, KIT 5 Muon-induced background Muons cause high energetic electron recoils However, muon-induced secondaries and especially muon-induced neutrons constitute low energetic background that scatters off nuclei Before veto: (WIMPlike) evts/(kg·d) Benjamin Schmidt -All events -Fiducial events -Potential background for DM search Muon induced bolometer events (1504 kg·d)

EDELWEISS, IEKP, KIT 6 Quantification of muon flux and muon veto efficiency – measurements and MC simulation Muon veto efficiency 1 st method: (Measurement only) ε = (candidates in bolos/ evts in muon veto system) ε ≥ 92,8% (90%CL) (34/34 observed) 2 nd 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 ± )  /m 2 /d Benjamin Schmidt

EDELWEISS, IEKP, KIT 7 Calibrated Landau spectrum Benjamin Schmidt 6 MeV cut  = 95.5%  = 949  = 989

EDELWEISS, IEKP, KIT 8 Determination of single module efficiencies with trigger probability as funciton of energy Correction of measured µ-spectrum with energy dependent efficiency (bottom left in red) Single module efficiency: # muon spectrum / # corrected muon spectrum System efficiency via combination of known angular dependent muon flux with single module efficiencies ε ≥ 94,9% Plastic scintillator module 3 Efficiency of the µ-veto system - Method 3

EDELWEISS, IEKP, KIT 9 Topography of muon-induced events Benjamin Schmidt Distance of muon track to detectors -All detected muons (scaled) -Muons with secondaries in bolometers (coincidences) -Coincidences E Bolo < 1 MeV -Coincidences E Bolo > 1 MeV Lead identified as main target for the production of muon-induced neutrons Muon induced events produce multiple hits – 2 nd handle for rejection Benefits from more detectors and new PE shield in EDW-3

EDELWEISS, IEKP, KIT 10Benjamin Schmidt A: +4 V B: 1.5V C: 4 V D: +1.5V Nuclear recoil event discrimination & Surface event rejection- principle Bulk/Fiducial event Charge collected on electrodes A&C Surface event Charge collected on electrodes A&B NTD Phonon/Heat sensor = calorimetric measurement of total energy (T=18 mK,  T  0.2  K/keV ) Al electrodes Ionization measurement ( sub-keV resolution) Ionization yield Q = E I /E Rec 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! WIMP 100 GeV/c 2 Scatt. WIMP Recoil nucleus  E R ~10 keV A AA B B D D C C

EDELWEISS, IEKP, KIT 11 Outlook on data analysis Tasks: 1 st optimization of noise selection in optimal filter 2 nd adaptation of filtering techniques to new hardware Benjamin Schmidt Goal: improve stability and performance of optimal filter potential gain in low mass WIMP region Time domain Frequency domain

EDELWEISS, IEKP, KIT 12 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 channels Time-resolved measurements of charge propagation  Better understanding of detectors plus new possibilities for surface event discrimination Benjamin Schmidt Fiducial Volume > 600 g

EDELWEISS, IEKP, KIT 13 Results expected for background free measurement Benjamin Schmidt

EDELWEISS, IEKP, KIT 14 While I have got the word: The hike today The easy way - just follow me o’clock from the castle There are also GPS-data and descriptions available das-wildromantische- monbachtal/ /download.html#axzz2COBW0Gc2 Benjamin Schmidt

EDELWEISS, IEKP, KIT 15Benjamin Schmidt

EDELWEISS, IEKP, KIT 16 Upgrades towards EDELWEISS-3 Reducing background events Benjamin Schmidt

EDELWEISS, IEKP, KIT 17Benjamin Schmidt Outlook: µ-veto system of EURECA Requirements: 500 kg year exposure with expectation of < 1 evt Idea: Water Cherenkov detectors Attenuate n flux Active µ-veto system Minimize high-z material near cryostat Better mass to surface ratio for 1t scale experiment Assume: Minimized high-z material Γ n (n-yield per detector mass) Large number of crystals but higher mass/crystal 0.5 Γ single bolo interactions Need  86.3 %