Low Mass WIMP Search with the CDMS Low Ionization Threshold Experiment Wolfgang Rau Queen’s University Kingston

W. Rau – Sudbury, November CDMS Technology and CDMSlite Recent CDMSlite data SNOLAB Conclusions CDMS Technology and CDMSlite Recent CDMSlite data SNOLAB Conclusions Overview

W. Rau – Sudbury, November Phonon energy [keV] Ionization energy [keV eeq] Nuclear recoils from neutrons Electron recoils from β’s and γ’s Thermal coupling Thermal bath Phonon sensor Target e n Phonon signal (single crystal): measures energy deposition Ionization/scintillation signal: quenched for nuclear recoils (lower signal efficiency) Combination: efficient rejection of electron recoil background Phonon signal Charge signal Electron recoil (ER)Nuclear recoil (NR) Cryogenic Dark Matter Detection

W. Rau – Sudbury, November In Vacuum In Matter Electron gains kinetic energy (E = q · V  1 eV for 1 V potential) 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 Neganov-Luke Phonons

W. Rau – Sudbury, November Background dilution with Luke Effect Electron Recoil Spectrum Energy Number of Counts Nuclear Recoil Spectrum

W. Rau – Sudbury, November SuperCDMS Collaboration California Institute of Technology CNRS/LPN Durham University Fermi National Accelerator Laboratory NISER NIST Northwestern University PNNL Queen’s University Santa Clara University SLAC/KIPA South Dakota School of Mines & Technology Southern Methodist University Stanford University Texas A&M 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 University of Toronto

W. Rau – Sudbury, November Basic configuration +2 V0 V -2 V0 V Electric field calculation Implementation Germanium single crystals (620 g modules) Thermal readout: superconducting phase transition sensor (TES); T c = 50 – 100 mK Charge readout: Al electrode; interleaved with phonon sensors Low bias voltage (4 V) in regular operation One detector: ~70 V for part of the time CDMSlite configuration 0 V -70 V

W. Rau – Sudbury, November Implementation (Soudan setup) Stack detectors (3) for mounting (“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 (~700 m below ground)

W. Rau – Sudbury, November Surface events 210 Pb source 65,000 betas 0 events leakage 15,000 surface NRs Trigger Efficiency (good detector) Total Phonon Energy [keV] Events per bin Recoil Energy [keVee] 10.3 keV (Ge) cosmogenic activation Sample of low background gamma data Detector Performance (iZIPs)

W. Rau – Sudbury, November CDMSlite R1 data First ‘proof-of-principle’ data set: 6 kg days Threshold: ~170 eVee, limited by vibrations Overall sensitivity limited by background Problematic electric field configuration at the edge of the detector not addressed HV instability of order of 8 % (affects energy resolution at the same level) Lindhard model for ER-NR conversion Energy Counts/time Full energy peak Reduced Luke amplification

W. Rau – Sudbury, November CDMSlite R1 SuperCDMS iZIP (LT) LUX CoGeNT CDMS Si

W. Rau – Sudbury, November CDMSlite R2 Improvements Vibrations/Threshold Monitor vibrations (accelerometer at cryocooler)  achieve threshold of 74 eVee (  ~5) Interrupt measurement to service cryocooler  reduced vibration allow for lower hardware threshold: achieve 56 eVee

W. Rau – Sudbury, November CDMSlite R2 Improvements HV stability / base temperature Clean and seal HV distribution board, operate under N 2  moderately improved stability (~5 % over entire period) Account for amplitude shift due to change in base temperature (~8 % effect) Additional jumps in gain (before and after “green” period; unknown origin) – correct with ad-hoc factor

W. Rau – Sudbury, November CDMSlite R2 Improvements Position dependence / Fiducial Volume New fit, accounts better for observed variation in pulse shape  Improve energy resolution  Good position information for fiducialization

W. Rau – Sudbury, November CDMSlite R2 Analysis Pulse Shape Cut Efficiency Fit pluses to three templates: good pulse / low-frequency noise / “glitches” Compare fit quality for all three templates Remove events with better fit to non-pulse templates Measure efficiency: take template pulse, scale to low energy, add real noise, fit like data, determine fraction that passes cuts Pulse Shape Cut Efficiency Period 1 Period 2 Energy [keVee]

W. Rau – Sudbury, November CDMSlite R2 Analysis Fiducial Volume Efficiency Use activation lines from 71 Ge deacy (t ½ = 11.4 days) to determine fraction / location of reduced energy events  mostly outer (as expected); ~86 % have full energy Determine fraction of events in peak that pass cut: ~55-60 % Measure efficiency at lower energy with pulse simulation (template + noise)

W. Rau – Sudbury, November CDMSlite R2 Analysis “The Spot” A localized background appeared in the second period at low energy Origin not clear (similar effects have been observed in the past as well) Fortunately: mostly removed by fiducial volume cut (slightly tighter cut in period 2 due to spot events)

W. Rau – Sudbury, November CDMSlite R2 Analysis Error Propagation Use full uncertainty distribution for each input parameter Draw parameter randomly according to their distribution Calculate final efficiency / limit with the drawn values Repeat 1000 times: median is the final result; uncertainty given by distribution Use same method for nuclear recoil energy scale model (Lindhard parameter)

W. Rau – Sudbury, November CDMSlite R2 Analysis Final Spectrum

W. Rau – Sudbury, November CDMSlite R1 SuperCDMS iZIP (LT) CRESST 2015 DAMIC LUX CoGeNT CDMS Si

W. Rau – Sudbury, November CDMSlite R3 at Soudan Test double sided readout Use different detector – determine what of our observations is detector specific Exposure < R2 Use analysis to develop a blinding scheme for HV operation Improve 2-template fit If we are lucky threshold is lower

DAMA CDMS Si LUX 2013 DEAP CDMS II 2015 DAMIC 2012 SuperCDMS LT 2014 CRESST 2015 CDMSlite 2015 Solar Neutrinos Atmospheric Neutrinos Si HV Si iZIP Ge HV Ge iZIP LZ W. Rau – Sudbury, November SuperCDMS at SNOLAB Initial payload includes mix of standard and HV detectors (Ge, Si) Room for significant additional payload e.g. from EURECA (CRESST, EDELWEISS) or advanced HV dets. Funding: Selected by DOE/NSF as one of two “G2” WIMP search experiments Total project cost: ~$35M, including $3.4M from Canada Schedule: expected start of operation in 2019 Setup holds up to ~260 kg detectors Shielding includes water tanks (n), lead (  ), poly (n from inner parts)

W. Rau – Sudbury, November DAMA CDMS Si LUX 2013 DEAP CDMS II 2015 DAMIC 2012 SuperCDMS LT 2014 CRESST 2015 CDMSlite 2015 Solar Neutrinos Atmospheric Neutrinos Si HV Si iZIP Ge HV Ge iZIP LZ SuperCDMS at SNOLAB Goal Sensitivity

W. Rau – Sudbury, November Cryogenic Underground TEst facility CUTE Test SuperCDMS/EURECA Towers Background discrimination studies Measure 3 H / 32 Si background Install in 2016, commission in 2017

W. Rau – Sudbury, November Conclusions CDMSlite provides excellent sensitivity for low mass WIMPs (<~6 GeV/c 2 ) Improvements for SuperCDMS SNOLAB include: o larger detectors o improved phonon sensors o double sided readout o increased HV o goal threshold 10 eV o limiting background: cosmogenic 3 H / 32 Si iZIPs provide optimal sensitivity in intermediate mass range (~5-15 GeV/c 2 )