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Data analysis and background investigation in the EDELWEISS direct d ark m atter search

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. <v> ≈ 230 km/s. t. t.

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Data analysis and background investigation in the EDELWEISS direct d ark m atter search

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  1. Data analysis and background investigation in the EDELWEISS direct dark matter search

  2. Earth moves through DM halo • ρDM = 0.3 GeV/cm3 The corner of the dark we are looking at   Production t Annihilation ER ~ 10 keV q q <v> ≈ 230 km/s t t M ~ 100 GeV/c2 Scattering Benjamin Schmidt

  3. WIMP(c) direct detection • ER ~ 10 keV, Count rate:< 1 evt / (kg·year) Ge, CS2, C3F8,He3 Ge, Si 10% energy Ionization Target LXe, LAr Heat Al2O3, LiF 100% energyslowest,cryogenics Light 1% energyfastest,no surface effects NaI, LXe, LAr CaWO4, BGO WIMP Benjamin Schmidt

  4. m The EDELWEISS experiment Shielding: ~ 4850 mwe m-flux (lab): ~ 5 m / m2 / day • Sensitivity Goal: sc-n= a few·10-45cm2(< 10-3evt/kg.d) • Cryogenic installation (18 mK) : • Can host up to 40 kg of bolometer • Shieldings : • Clean room + deradonized air • Active muon veto (>98% coverage) • PEshield50 cm • Leadshield20 cm • Background studies : • Radon detector down to few mBq/m3 • thermal neutron monitoring (He3det.) • Muon-veto – bolometercoincidences • StrongAmBe source calibrations • Study of muon induced neutrons (liquidscintillator 1 m3 neutron counter) µ Polyethylene shield Pb shield Cryostat with bolometers µ-veto µ-n counter Benjamin Schmidt

  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: 0.008 (WIMPlike) evts/(kg·d) Muon induced bolometer events (1504 kg·d) • All events • Fiducial events • Potential background for DM search Benjamin Schmidt

  6. Quantification of muon flux and muon veto efficiency – measurements and MC simulation • Muon veto efficiency • 1st 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 curvesε = (97.7 ± 1.5) % • Irreducible background flux 2·10-4evts/(kg·d) (MPV) • Muon flux (horizontal area) • Measurement + MC simulation: (5.4 ± 0.2 +0.5-0.9) m/m2/d Benjamin Schmidt

  7. Topography of muon-induced events • 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 neutrons Muon induced events produce multiple hits – 2nd handle for rejection Benefits from more detectors and new PE shield in EDW-3 Benjamin Schmidt

  8. Nuclear recoil event discrimination & Surface event rejection- principle Recoil nucleus  ER~10 keV Scatt. WIMP WIMP 100 GeV/c2 Count rate: < 1 evt/kg/year! Event discrimination via simultaneous charge and phonon measurement NTD Phonon/Heat sensor = calorimetric measurement of total energy (T=18 mK, DT  0.2mK/keV) Al electrodes Ionization measurement ( sub-keV resolution) Ionization yield Q = EI/ERec nuclear recoils have ~1/3 Q of e-recoils A B A B A A: +4 V B: 1.5V Fiducial volume C: 4 V D: +1.5V C D C D Bulk/Fiducial event Charge collected on electrodes A&C Surface event Charge collected on electrodes A&B Benjamin Schmidt

  9. Outlook on data analysisTasks: 1st optimization of noise selection in optimal filter2nd adaptation of filtering techniques to new hardware Frequency domain Time domain Goal: improve stability and performance of optimal filterpotential gain in low mass WIMP region Benjamin Schmidt

  10. 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 Fiducial Volume > 600 g Benjamin Schmidt

  11. Results expected for background free measurement Benjamin Schmidt

  12. While I have got the word: • The hike today • The easy way - just follow me • 13.30 o’clock from the castle • There are also GPS-data and descriptions available • http://www.outdooractive.com/de/wanderung/nordschwarzwald/durch-das-wildromantische-monbachtal/1398559/download.html#axzz2COBW0Gc2 Benjamin Schmidt

  13. Benjamin Schmidt

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