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Dark Matter Search with SuperCDMS

Dark Matter Search with SuperCDMS. Results, Status and Future Wolfgang Rau Queen’s University. Introduction SuperCDMS technology Implementation for SuperCDMS Soudan Results from SuperCDMS Soudan Status and plans for SuperCDMS SNOLAB. SuperCDMS Collaboration.

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Dark Matter Search with SuperCDMS

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  1. Dark Matter Search with SuperCDMS Results, Status and Future Wolfgang Rau Queen’s University

  2. Introduction SuperCDMS technology • Implementation for SuperCDMS Soudan • Results from SuperCDMS Soudan • Status and plans for SuperCDMS SNOLAB W. Rau - CAP 2014

  3. SuperCDMS Collaboration • California Institute of Technology CNRS/LPN Fermi National Accelerator Laboratory • Massachusetts Institute of Technology PNNL Queen’s University • Santa Clara University SLAC/KIPAC Southern Methodist University • Stanford University Syracuse University Texas A&M Universidad Atónoma de Madrid • University of British Columbia University of California, Berkeley • University of Colorado Denver University of Evansville University of Florida • University of Minnesota University of South Dakota W. Rau - CAP 2014

  4. Thermal bath Thermal coupling Phonon sensor e n + + + - - Target - Ionization energy [keVeeq] - + + - - + + - + + + + Phonon energy [keV] - - - - • SuperCDMS Technology • Phonon signal (single crystal): measures energy deposition • Ionization signal (semiconductor): • quenched for nuclear recoils (lower signal efficiency) • Combination:efficient rejection of electron recoil background Electron recoils from β’s and γ’s Phonon signal Electron recoil (ER) Nuclear recoil (NR) Nuclear recoils from neutrons Charge signal W. Rau - CAP 2014

  5. Neganov-Luke Phonons - - + + In Vacuum Electron gains kinetic energy (E = q · V  1 eV for 1 V potential) - In Matter Deposited energy in crystal lattice: Neganov-Luke phonons  V, # charges - • Luke phonons mix charge and phonon signal  reduced discrimination • Apply high voltage  large final phonon signal, measures charge!! • ER much more amplified than NR  gain in threshold; dilute background from ER W. Rau - CAP 2014

  6. Background dilution with Luke Effect Electron Recoil Spectrum Nuclear Recoil Spectrum Number of Counts Energy W. Rau - CAP 2014

  7. Implementation – SuperCDMS Soudan +2 V 0 V 0 V CDMSlite configuration Basic configuration Electric field calculation -2 V -69 V 0 V • Germanium single crystals (620 g modules) • Thermal readout: superconducting phase transition sensor (TES); Tc = 50 – 100 mK • Charge readout: Al electrode; interleaved with phonon sensors • Low bias voltage (4 V) in regular operation • One detector: ~70 V for some time W. Rau - CAP 2014

  8. Implementation (Soudan) • Stack detectors (3) to mount (“tower”) • 5 towers deployed in cryostat (~9 kg Ge) • Shielded with PE (for neutrons), Pb (gammas) and muon veto (cosmic radiation) • Located at Soudan Underground Lab (Minnesota) to shield from cosmic radiation W. Rau - CAP 2014

  9. Detector Performance Surface events W. Rau - CAP 2014

  10. Past Analysis Approaches • “Classic” CDMS approach: minimize expected BG (<1 for data set under analysis)  threshold ~10 keV(Erecoil: use Q signal for Luke correction) • Low-threshold extension: strongly rising WIMP spectrum at low E  improved sensitivity in spite of BG(no surface event discrimination; ENR: Luke correction based on mean yield) • CMDSlite: no discrimination, but even lower threshold; BG diluted (ENR: based on Lindhard model) CDMS II, 2010 ~200 kgd after cuts CDMS II, 2011 ~6 kgd after cuts ~100 kgd after cuts W. Rau - CAP 2014

  11. Results – before 2014 PICASSO 2012 CDMS low threshold 2011 CDMSlite 2013 CoGeNT DAMA 2000 CDMS Si 2013 CDMS Si2013 XENON 10 S2 (2011) CRESST 2011 EDELWEISS II 2011 SuperCDMS low threshold 2014 CDMS2010 XENON 1002012 LUX 2013 8B W. Rau - CAP 2014

  12. SuperCDMS Soudan – Latest Data • Low-threshold method, but now with: • Surface event rejection with charge signal (interleaved electrodes) AND phonon signal (sensors on top and bottom!) • Edge event rejection with charge signal (was available in CDMS) AND phonon signal (new sensor layout) • New Analysis method for improved efficiency (Boosted Decision Tree) • Background model to train BDT (cosmogenics, 210Pb chain): MC to get distributions; use scaled pulses + real noise to generate `events’ (gammas for BG, neutrons for signal) • Optimize tree for different WIMP masses (5, 7, 10, 15 GeV/c2) • BG model only for BDT training; efficiency measured with neutrons Data Quality Trigger Efficiency All before BDT (e.g. singles, veto,charge fid.vol.) BDT (phonon and chargeampl., phonon fiducial volume) W. Rau - CAP 2014

  13. SuperCDMS Soudan – Results and Future • BG model predicts ~6 events – BUT: difficult to make good prediction in this low energy range  only set upper limit • “Open box”: observed 11 events • 3 highest energy events in detector with shorted outer charge channel CDMSlite • Probe new parameter space between 4 and 6 GeV/c2 • Incompatible with CoGeNT interpretation as NR signal from WIMPs • Standard (high threshold) analysis in progress / additional CDMSlite data collected • DM search until fall (expect to be limited by cosmogenic/radiogenic BG by then) • Systematic studies until spring 2015 Lux http://arxiv.org/abs/1402.7137 Accepted by PRL (May 21) W. Rau - CAP 2014

  14. SuperCDMS at SNOLAB R&D • Larger modules (1.4 kg Ge/0.6 kg Si) • First prototypes are being tested using existing hardware • Mechanical prototype for new tower exists • Developing dedicated HV detectors • New SQUIDs for improved phonon performance (from NIST, USA) • New low noise charge amplifier (HEMTs from CNRS/LPN, France) • Compactified readout electronics (one 3U board / det. replaces 2 9U boards and digitizer) • DAQ: MIDAS based (developed by UBC) 100 mm iZIP: 33 mm high, 100 mm  1.4 kg Ge / 600 g Si W. Rau - CAP 2014

  15. SuperCDMS at SNOLAB • ~100 kg Ge / ~10 kg Si • 1 tower of dedicated HV detectors • Setup for ~400 kg detector mass for later upgrade • EURECA indicated interest in contributing additional target mass • Shielding includes neutron veto (scintillator) • Timing: start construction in early 2015; takes ~2 years to build • Funding: $3.4M from CFI / waiting for G2 decision in the US (expected anytime now) W. Rau - CAP 2014

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