Low Mass WIMP Search with the CDMS Low

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

W. Rau – Sudbury, November 2015 Overview • CDMS Technology and CDMSlite • Recent CDMSlite data • Super. CDMS @ SNOLAB • Conclusions 2

W. Rau – Sudbury, November 2015 Cryogenic Dark Matter Detection Thermal coupling Phonon sensor ++ + + Target + + n- -- Phonon signal -- -- --- e + Charge signal Electron recoil (ER) Nuclear recoil (NR) • Phonon signal (single crystal): measures energy deposition • Ionization/scintillation signal: quenched for nuclear recoils (lower signal efficiency) • Combination: efficient rejection of electron recoil background Ionization energy [ke. V eeq] Thermal bath Electron recoils from β’s and γ’s Nuclear recoils from neutrons Phonon energy [ke. V] 3

W. Rau – Sudbury, November 2015 - Neganov-Luke Phonons In Vacuum + - In Matter - - • • • Electron gains kinetic energy (E = q · V 1 e. V 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 4

W. Rau – Sudbury, November 2015 Background dilution with Luke Effect Number of Counts Electron Recoil Spectrum Nuclear Recoil Spectrum Energy 5

W. Rau – Sudbury, November 2015 Super. CDMS Collaboration California Institute of Technology CNRS/LPN Fermi National Accelerator Laboratory PNNL 6 Queen’s University NISER Texas A&M University of California, Berkeley University of Evansville University of Minnesota Northwestern University Santa Clara University South Dakota School of Mines & Technology Stanford University NIST Durham University SLAC/KIPA Southern Methodist University of British Columbia University of Colorado Denver University of Florida University of South Dakota University of Toronto

W. Rau – Sudbury, November 2015 7 Implementation +2 V 00 VV Basic configuration CDMSlite configuration Electric field calculation -2 V-700 VV • Germanium single crystals (620 g modules) • Thermal readout: superconducting phase transition sensor (TES); Tc = 50 – 100 m. K • 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

W. Rau – Sudbury, November 2015 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) 8

W. Rau – Sudbury, November 2015 Detector Performance (i. ZIPs) 210 Pb source 65, 000 betas 0 events leakage 15, 000 surface NRs Surface events Trigger Efficiency (good detector) Sample of low background gamma data Events per bin 1. 0 0. 5 0. 0 0 2 4 9 6 8 10 12 Total Phonon Energy [ke. V] 10. 3 ke. V (Ge) cosmogenic activation Recoil Energy [ke. Vee]

W. Rau – Sudbury, November 2015 10 CDMSlite R 1 data Counts/time • First ‘proof-of-principle’ data set: 6 kg days • Threshold: ~170 e. Vee, 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 Full energy peak Reduced Luke amplification Energy

W. Rau – Sudbury, November 2015 11 CDMS Super lite R 1 CDMS LUX T) i. ZIP (L Co. Ge. NT CDMS Si

W. Rau – Sudbury, November 2015 CDMSlite R 2 Improvements Vibrations/Threshold • Monitor vibrations (accelerometer at cryocooler) achieve threshold of 74 e. Vee ( ~5) • Interrupt measurement to service cryocooler reduced vibration allow for lower hardware threshold: achieve 56 e. Vee 12

W. Rau – Sudbury, November 2015 CDMSlite R 2 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 13

W. Rau – Sudbury, November 2015 CDMSlite R 2 Improvements Position dependence / Fiducial Volume • New fit, accounts better for observed variation in pulse shape Improve energy resolution Good position information for fiducialization 14

W. Rau – Sudbury, November 2015 15 CDMSlite R 2 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 [ke. Vee]

W. Rau – Sudbury, November 2015 CDMSlite R 2 Analysis Fiducial Volume Efficiency • Use activation lines from 71 Ge deacy (t½ = 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) 16

W. Rau – Sudbury, November 2015 CDMSlite R 2 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) 17

W. Rau – Sudbury, November 2015 CDMSlite R 2 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) 18

W. Rau – Sudbury, November 2015 CDMSlite R 2 Analysis Final Spectrum 19

W. Rau – Sudbury, November 2015 20 CDMS Super lite R 1 CDMS ST 20 15 LUX ES T) i. ZIP (L CR DAMIC Co. Ge. NT CDMS Si

W. Rau – Sudbury, November 2015 CDMSlite R 3 at Soudan • Test double sided readout • Use different detector – determine what of our observations is detector specific • Exposure < R 2 • Use analysis to develop a blinding scheme for HV operation • Improve 2 -template fit • If we are lucky threshold is lower 21

W. Rau – Sudbury, November 2015 22 Super. CDMS at SNOLAB C 20 RES 15 ST DAMIC 2012 DAMA i SS M CD te Sli M 5 CD 201 Ge i. ZIP P Si i. ZI V Ge H V Si H • Setup holds up to ~260 kg detectors • Shielding includes water tanks (n), lead ( ), poly (n from inner parts) DAMA Super. CDMS LT 2014 CDMS II 2015 3 1 LUX 20 Solar Neutrinos DEAP LZ Atmospheric Neutrinos • 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 “G 2” WIMP search experiments • Total project cost: ~$35 M, including $3. 4 M from Canada • Schedule: expected start of operation in 2019

W. Rau – Sudbury, November 2015 23 Super. CDMS at SNOLAB Goal Sensitivity C 20 RES 15 ST DAMIC 2012 i SS M CD V Si H te Sli M 5 CD 201 Ge i. ZIP P Si i. ZI V Ge H DAMA Super. CDMS LT 2014 CDMS II 2015 13 Solar Neutrinos LUX 20 DEAP LZ Atmospheric Neutrinos

W. Rau – Sudbury, November 2015 Cryogenic Underground TEst facility CUTE • • Test Super. CDMS/EURECA Towers Background discrimination studies Measure 3 H / 32 Si background Install in 2016, commission in 2017 24

W. Rau – Sudbury, November 2015 Conclusions • CDMSlite provides excellent sensitivity for low mass WIMPs (<~6 Ge. V/c 2) • Improvements for Super. CDMS SNOLAB include: o larger detectors o improved phonon sensors o double sided readout o increased HV o goal threshold 10 e. V o limiting background: cosmogenic 3 H / 32 Si • i. ZIPs provide optimal sensitivity in intermediate mass range (~5 -15 Ge. V/c 2) 25