SCENE Results for Liquid Argon: Field Dependence of Scintillation and Ionization from Nuclear Recoils Charles Huajie Cao Princeton University On Behalf of SCENE Collaboration (Scintillation and Ionization Efficiency of Noble Elements) UCLA DM 2014 1 Liquid Argon (LAr) as WIMP Target Scintillation / S1: Excellent pulse shape discrimination (PSD) of nuclear (NR) versus electron recoils (ER) Single-‐phase S1 only DEAP SNOLAB CLEAN SNOLAB Ionization / S2: enables position reconstruction and additional ER discrimination Dual-‐phase S1+S2 DarkSide Gran Sasso UCLA DM 2014 ArDM Canfranc 2 Scintillation and Ionization Yield for Nuclear Recoils (NR) • • Knowledge of those quantities is required to convert a NR signal to the deposited energy They decide the energy threshold of LAr detectors • Scintillation: Yield for low energy (<25 keVr) NR has not been precisely determined in the literature Effects of applied electric field (both on PSD and scintillation yield) need to be characterized for two-‐phase Ar time projection chamber (LAr-‐TPC) • Ionization: One recent result from LLNL at 6.7 keVr (arXiv: 1402.2037) No comprehensive measurement of the ionization yield for the WIMP search energy range C. Regenfus et. al., J. Phys.: Conf. Ser. 375 (2012) 012019 UCLA DM 2014 3 Nuclear Recoils from Elastic Scattering of Neutrons LAr-‐TPC Mono-‐energetic Neutrons ERecoil/ENeutron Scattering angle, Θ n-Ar Elastic Scattering 10-1 Neutron detector 10-2 The Challenges 10-3 0 20 40 60 80 100 120 140 160 180 θ[deg] 1. Unambiguously select single NRs of a known energy 2. Compact detector geometry to minimize multiple scatterings UCLA DM 2014 4 7Li(p, n)7Be Reaction Ref: C.A.Burke et al., Phys. Rev. C 10, 1299 (1974) -‐ Jun 2013 Generate neutrons with En on the order of MeV with precise energy and high flux -‐ Oct 2013 Vertical offset in ( ) to be subtracted UCLA DM 2014 5 Proton Beam at University of Notre Dame SCENE setup ~ 10-‐4 neutrons per pulse through LAr-‐TPC • period = 101.5 ns or its multiples used 203, 406, 508, 812 ns • max current = 300 nA used ~50 nA • beam angle spread at target < 0.006 deg • ±1 keV mean uncertainty • ±2 keV spread • 10 MeV maximum UCLA DM 2014 6 Experimental Layout Jun 2013 setup (Oct 2013 setup) 200 μg/cm2 25.4° (35.6°) 73 cm (82.4 cm) 71 cm 5” EJ301: Organic Liquid Scintillator Detector from Eljen Technology Polyethylene shielding between LiF and EJ301 omitted for clarity UCLA DM 2014 7 LAr-‐TPC PMT Active LAr volume: 76 mm x 69 mm dia. Inactive LAr volume: 15 mm, annular 76 mm Hamamatsu 3” PMT R11065 (QE 420nm: 33%) Gas Reflector: 3M Vikuiti ITO plated fused silica window 7 mm Anode Extraction grid Liquid Wavelength shifter: 200 μg/cm2 1,1,4,4-‐ Tetraphenyl-‐1,3-‐butadiene (TPB) on reflector and windows Reflector 76 mm Field cage rings Electrodes: 20 nm Indium Tin Oxide (ITO) on fused silica windows Max anode voltage tested: +4.5 kV Max cathode voltage tested: -‐8.0 kV Cathode Grid: SS hexagonal mesh, GND 69 mm Drift field and extraction field can be set independently ITO plated fused silica window PMT 98 mm UCLA DM 2014 8 LAr-‐TPC PMT Active LAr volume: 76 mm x 69 mm dia. Inactive LAr volume: 15 mm, annular ITO plated fused silica window 76 mm Hamamatsu 3” PMT R11065 (QE 420nm: 33%) Gas 7 mm Extraction grid Liquid Reflector: 3M Vikuiti Wavelength shifter: 200 μg/cm2 1,1,4,4-‐ Tetraphenyl-‐1,3-‐butadiene (TPB) on reflector and windows 1600 All Scatters Reflector 1800 Counts/0.5 PE Anode 76 mm 1400 Field cage rings Electrodes: 20 nm Indium Tin Oxide (ITO) on Scatters Single fused s ilica w indows 1200 1000 Max anode voltage tested: +4.5 kV 800 Max cathode voltage tested: -‐8.0 kV 600 400 Grid: SS hexagonal mesh, GND 200 Geant4 Simulation 10.8 keV Drift field and extraction field can be set 0 independently 0 5 10 15 20 25 30 Energy [keV] Cathode 69 mm ITO plated fused silica window PMT 98 mm UCLA DM 2014 9 Ntof [ns] Data (10.8 keV, Edrift = 1000 V/cm) 180 TPCtof: time difference between the proton-‐ beam-‐on-‐ target and the TPC signal 25 160 140 20 Neutrons! 120 100 Ntof: time difference between the proton-‐ beam-‐on-‐target and the neutron detector signal 15 80 60 10 40 Photons! 20 F90: PSD parameter in LAr the fraction of light detected in the first 90 ns of an event 5 0 1 0.9 -20 0 20 40 60 80 100 120 TPCtof [ns] 0 Npsd: peak over area in the neutron detector LAr-TPC (a) Cerenkov 10 Neutrons Neutron Detector (b) 25 20 8 0.7 0.2 0.6 6 0.5 0.4 0.2 Photons -20 0 20 40 60 80 100 120 TPCtof [ns] 0.1 2 0.05 0 15 0.15 4 0.3 0 -40 0.3 0.25 0.8 0.1 Npsd f90 -20 -40 0 -20 UCLA DM 2014 10 Photons 5 Neutrons 0 20 40 60 80 100 120 140 160 180 Ntof [ns] 10 0 105 All Coincidence Events After Ntof & Npsd Cuts 4 10 After TPCtof Cut 103 Counts/0.5 PE Spectra after all cuts 102 10 1 1 f90 (a) Counts/PE Data (10.8 keV, Edrift = 1000 V/cm) 102 10 0 V/cm 250 1000 V/cm 200 Gaussian fits 150 S1 [PE] LAr-TPC 1 300 100 10 0.9 50 0.8 8 0.7 0.6 0 0 0.4 4 0.3 0.1 0 -40 10 15 20 25 30 35 40 S1 [PE] 6 0.5 0.2 5 2 After Ntof & Npsd Cuts! -20 0 20 40 Clear field dependence! SCENE, Phys. Rev. D 88, 092006 60 80 100 120 TPCtof [ns] 0 UCLA DM 2014 11 Measured with 22Na Plante, PRC 84, 045805 (2011) • positioned between the TPC and one EJ301 • Triggered on the EJ301 • Recorded TPC PMT waveforms and PMT trigger waveforms Trigger Efficiency LAr-‐TPC Trigger Efficiency 1 0.8 0.6 0.4 Two PMT AND 0.2 Two PMT OR 0 0 2 4 6 8 10 12 14 Signal amplitude [PE] Counts/PE 20.8 keV 1000V/cm 140 Two PMT AND 120 Two PMT OR (Rescaled) 100 80 60 40 20 : two PMT coincidence for TPC trigger 0 0 UCLA DM 2014 10 20 30 40 50 60 70 80 S1 [PE] 12 Light Yield Monitors: 83mKr Source + LED Mean 400 447.4 ± 8.7 260.1 ± 0.4 Sigma 21.24 ± 0.34 pol1_const 55.35 ± 4.78 pol1_slope -0.07832 ± 0.01648 300 200 132 131 130 1000 V/cm 0.2654 Amplitude 500 V/cm 500 41.93 / 37 300 V/cm Prob 100 V/cm χ 2 / ndf Bottom PMT 133 0 V/cm Kr Source Counts/5 PE! 600 LED Pulse Mean [PE] 83m 129 128 127 100 Drift field 126 0 100 150 200 250 300 350 400 450 S1 [p.e.] 125 0 Continuous recirculation during the beam run for maintaining 83mKr activity (1.2 kBq in Jun, 0.5 kBq in Oct) and LAr purity 4 6 8 stable within 1% from cathode voltage changes 83mKr: LY and electron lifetime calibration 2 10 Hours LED Pulse (added for Oct Run): PMT efficiency monitoring Continuously recorded at 1 Hz Top PMT efficiency was affected by S2. LED pulse provided calibration. UCLA DM 2014 13 S1 Relative to 83m Kr(0V/cm) Scintillation Efficiency of Nuclear Recoils 0.3 0.28 Systematic Errors % Preliminary Difference <6 between fitting to Gaussian and MC 0.26 0.24 TPCtof Cut 3 0.22 Ntof Cut 3 f90 Cut 2 Kr Light Yield 2 Recoil energy 2 TPC position 1 EJ301 position 1 0.2 0 V/cm 100 V/cm 200 V/cm 300 V/cm 1000 V/cm 0.18 0.16 0.14 10 20 30 40 50 60 Recoil Energy [keV] We are still: 1. validating all data points 2. improving the MC model to reduce the systematic error. UCLA DM 2014 14 1 Counts/bin f90 f90 PSD Distribution 0.9 0.8 0.7 0.6 120 80 0.4 60 40 0.2 20 0.1 0 0 f90 distribution of events within 1σ in NPE 100 0.5 0.3 10 20 30 40 50 60 70 80 ± 1σ Counts/bin 140 χ2 / ndf Prob Constant Mean Sigma 250 200 90 100 S1 [PE] 0 0 33.42 / 31 0.3505 208.9 ± 4.2 28.24 ± 0.18 9.893 ± 0.204 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 f90 20.8 keV Edrift = 200V/cm 150 100 50 0 0 10 20 30 40 50 60 70 80 90 100 S1 [PE] UCLA DM 2014 15 f90 PSD Distribution f90 0 V/cm 0.8 0.7 0.6 0.5 0.4 Preliminary 0.3 10 20 30 10% 50% 65% 80% 90% Mean 40 50 60 Recoil energy [keV] We are investigating the systematic errors. UCLA DM 2014 16 f90 PSD Distribution f90 1000 V/cm 0.8 0.7 0.6 0.5 0.4 Preliminary 0.3 10 20 30 10% 50% 65% 80% 90% Mean 40 50 60 Recoil energy [keV] We are investigating the systematic errors. UCLA DM 2014 17 f90 PSD Distribution f90 Median f90 0.75 0.7 0.65 0.6 0 V/cm 0.55 200 V/cm Preliminary 0.5 0.45 10 20 30 300 V/cm 1000 V/cm 40 50 60 Recoil energy [keV] We are investigating the systematic errors. UCLA DM 2014 18 8000 (a) χ2 / ndf Prob Constant Mean Sigma 7000 6000 17.13 / 17 0.4457 8212 ± 34.2 1087 ± 1.0 266.2 ± 1.0 5000 70 (b) 60 χ2 / ndf Prob Constant Mean Sigma 18.25 / 28 0.9198 60.8 ± 2.4 317.3 ± 2.8 82.81 ± 3.00 50 40 4000 NR 57.6 keV 30 3000 83mKr 2000 20 10 1000 0 0 S2 yield [PE/keV] Counts/10 PE Counts/ 50 PE Ionization Yield at Eextraction = 3.0 kV/cm 500 45 40 35 30 1000 1500 16.5 26.1 35.7 57.6 83m Kr 2000 2500 3000 S2 [PE] 100 200 300 400 500 600 700 800 900 1000 S2 [PE] keV keV keV keV Preliminary 20 This increase in S2 yield is correlated with the decrease in S1 yield. 15 10 (b) 5 0 100 200 • continuously determined with 83mKr • Improved from 40 to 120 μs through the run • lifetime correction has been applied in the plots We observed increase of S2 yield with larger drift field, for both 83mKr source and NR. (a) 25 0 0 Electron lifetime 300 400 500 600 Drift field [V/cm] UCLA DM 2014 19 Ionization Yield at 6.7 keVr Measured at LLNL • Complementary measurements obtained at LLNL in the ionization channel at 6.7 keVr vs drift field 240 – 2100 V/cm • Dedicated quasi-monoenergetic epithermal neutron beam facility at LLNL • Observed large yields and similar recombination between electron and nuclear recoils • Qualitative agreement with SCENE results Detected number of electrons • Quantitative analysis and modeling of all existing LAr measurements is ongoing 70 2.82 keV – electron recoil 60 50 40 6.7 keV – nuclear recoil 30 T. Joshi, S. Sangiorgio, et al, arXiv:1402.2037 20 500 1000 Samuele Sangiorgio – LLNL – Feb 2014 UCLA DM 2014 1500 2000 2500 3000 Drift Field (V/cm) 20 Future step: Xe measurements The team behind the Xenon detector at UCLA UCLA DM 2014 21
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