The LUX-ZEPLIN Dark Matter Experiment Alden Fan for the LZ - PowerPoint PPT Presentation

The LUX-ZEPLIN Dark Matter Experiment Alden Fan for the LZ collaboration 
 Stanford/KIPAC/SLAC TAUP 2019 Toyama, Japan 9 September 2019

LZ collaboration 36 institutions, ~250 scientists, engineers, technicians IBS-CUP (Korea) Brandeis University (US) University of Alabama (US) LIP Coimbra (Portugal) Brookhaven National Lab (US) University of California, Berkeley (US) MEPhI (Russia) Brown University (US) University of California, Davis (US) Imperial College London (UK) Fermi National Accelerator Lab (US) University of California, Santa Barbara (US) Royal Holloway University of London (UK) Lawrence Berkeley National Lab (US) University of Maryland (US) STFC Rutherford Appleton Lab (UK) Lawrence Livermore National Lab (US) University of Massachusetts (US) University College London (UK) Northwestern University (US) University of Michigan (US) University of Bristol (UK) Pennsylvania State University (US) University of Rochester (US) University of Edinburgh (UK) SLAC National Accelerator Lab (US) University of South Dakota (US) University of Liverpool (UK) South Dakota School of Mines and Technology (US) University of Wisconsin – Madison (US) University of Oxford (UK) South Dakota Science and Technology Authority (US) University of Sheffield (UK) Texas A&M University (US) Black Hill State University (US) University at Albany (US) A. Fan (SLAC) TAUP2019 LZ Status 2

Dual-phase liquid xenon TPC • Looking for very low-energy nuclear recoils from WIMP dark matter • Particle scattering on Xe produces prompt scintillation (S1) and ionization electrons • Electrons drift up into gas phase to produce electroluminescence S2 • Full 3D reconstruction from S1-S2 time delay (z) and hit pattern (xy) • S2/S1 ratio for discrimination between electron recoils (ERs) and nuclear recoils (NR) A. Fan (SLAC) TAUP2019 LZ Status 3

LUX-ZEPLIN LZ TDR arXiv:1703.09144 Nested detectors Dual-phase Xe TPC LXe skin region Gd-loaded liquid scintillator High purity water A. Fan (SLAC) TAUP2019 LZ Status 4

Sanford Underground Research Facility • Located in Lead, SD (USA) in the Black Hills • LZ located at the 4850 level (~1.5 km underground) • 4300 m.w.e. overburden • Muon flux reduced by O(10 7 ) A. Fan (SLAC) TAUP2019 LZ Status 5

Xenon TPC 494 PMTs GAS PHASE AND ELECTROLUMINESCENCE REGION GAS PHASE AND 7 tonne active LXe SECTION VIEW ELECTROLUMINESCENCE REGION 5.6 tonne fiducial OF LXE TPC (1.5 m diameter x 1.5 m height) Top PMT array Anode LXe surface Anode LXe surface Side Skin PMTs Weir trough Weir trough Gate TPC field cage Gate Skin PMT Skin PMT 50 kV cathode HV HV CONNECTION TO CATHODE Cathode grid 4x grid electrodes Reverse-field region Side skin PMT mounting plate Gas Xe circulation @ 500 slpm Bottom PMT array (turnover full mass in 2.5 days) A. Fan (SLAC) TAUP2019 LZ Status 6

Outer Detector and Skin Region The Skin The OD • 2 tonnes of LXe surrounding the TPC • 17 tonnes Gd-loaded liquid scintillator in acrylic vessels • 1” and 2” PMTs at the top and bottom of the skin region • 120 8” PMTs mounted in the water tank • Lined with PTFE to maximize light collection efficiency • Anti-coincidence detector for γ -rays and neutrons • Anti-coincidence detector for γ -rays • Observe ~8.5 MeV γ -rays from thermal neutron capture • Tag individual neutrons and γ -rays • Draw on experience from • Characterize BGs in situ Daya Bay See talk by B. Penning 
 “The LZ Outer Detector” 
 → Enables discovery potential DM16 Thu afternoon A. Fan (SLAC) TAUP2019 LZ Status 7

D.S. Akerib et al (LZ collaboration) 2018 arXiv:1802.06039 Background suppression No veto Xe skin & OD veto 10 2 140 140 Combined veto system allows to define a fiducial volume at 120 120 80% of active volume. 10 1 100 100 counts/tonne/year z [cm] z [cm] 80 80 60 60 10 0 40 40 20 20 10 − 1 0 0 0 2 20 2 30 2 0 2 20 2 30 2 40 2 50 2 60 2 70 2 40 2 50 2 60 2 70 2 r 2 [cm 2 ] r 2 [cm 2 ] Expected BG NR cts / 1000 days 
 1.03 10.43 in 5.6t FV in 6-30 keV nr : 3.2 5.6 NR BG equivalent fiducial volume: A. Fan (SLAC) TAUP2019 LZ Status 8

Background sources and mitigation • Detector materials • Xenon contaminants — 85 Kr, 39 Ar • Radio-assay campaign with gamma- • Charcoal chromatography @ SLAC screening, ICPMS, NAA • Cosmogenics and externals • Rn emanation • 4300 m.w.e. underground at Sanford • Four Rn emanation screening sites Underground Research Facility in Lead, SD • Target Rn activity: 2 μ Bq/kg • Instrumented Xe skin region • Rn daughters and dust on surfaces • Gd-LS outer detector • High purity water shield • TPC assembly in Rn-reduced cleanroom • Dust <500 ng/cm 3 on all LXe wetted Many sources of BG surfaces Many methods for BG mitigation • Rn-daughter plate-out on TPC walls <0.5 See talk by A. Kamaha 
 mBq/m 2 “Material Assay and Cleanliness for the 
 LUX-ZEPLIN Experiment” DM4 Mon afternoon A. Fan (SLAC) TAUP2019 LZ Status 9

Plot for Background Energy Spectrum in inner 1T approval Changes: thinner lines, moved labels, Expected backgrounds LZ Preliminary aspect ratio 10 − 4 5.6 tonne fiducial volume, 1000 live-days 
 l Rate [counts/kg/day/keV] a o t T ● DRU spectrum in inner 1T 136 Xe 1.5-6.5 keV ee (6-30 keV nr ) 
 fiducial volume 222 Rn single scatters, anti-coincidence with vetoes Note: the 60 Co, 238 U, 232 Th spectra 10 − 5 Solar ν from detector materials are Background Source ER [cts] NR [cts] 220 Rn combined into ‘Detector’ to reduce ER Det. + Sur. + Env. clutter, but are separate PDFs in 85 Kr Detector components 9 0.07 10 − 6 the likelihood Plot for Background Energy Spectrum in inner 1T 0 50 100 150 200 approval Dispersed Radionuclides — Rn, Kr, Ar 819 — Electronic recoil energy [keV] Changes: thinner lines, moved labels, NR LZ Preliminary aspect ratio 10 − 3 Laboratory and Cosmogenics 5 0.06 10 − 4 Rate [counts/kg/day/keV] ● DRU spectrum in inner 1T Surface Contamination and Dust 40 0.39 10 − 5 fiducial volume 8 B 10 − 6 14 Physics Backgrounds — 2 β decay, neutrinos* 322 0.51 Total Note: the 60 Co, 238 U, 232 Th spectra 10 − 7 Det. + Sur. + Env. hep from detector materials are 10 − 8 Total 1195 1.03 combined into ‘Detector’ to reduce 10 − 9 clutter, but are separate PDFs in 10 − 10 After 99.5% ER discrimination, 50% NR e ffi ciency 5.97 0.51 DSN A the likelihood t m 10 − 11 0 20 40 60 80 100 * not including 8 B and hep D.S. Akerib et al (LZ collaboration) 2018 arXiv:1802.06039 Nuclear recoil energy [keV] A. Fan (SLAC) TAUP2019 LZ Status 10 14

Plot for Background Energy Spectrum in inner 1T approval Changes: thinner lines, moved labels, Expected backgrounds LZ Preliminary aspect ratio 10 − 4 5.6 tonne fiducial volume, 1000 live-days 
 l Rate [counts/kg/day/keV] a o t T ● DRU spectrum in inner 1T 136 Xe 1.5-6.5 keV ee (6-30 keV nr ) 
 fiducial volume 222 Rn single scatters, anti-coincidence with vetoes Note: the 60 Co, 238 U, 232 Th spectra 10 − 5 Solar ν from detector materials are Background Source ER [cts] NR [cts] 220 Rn combined into ‘Detector’ to reduce ER Det. + Sur. + Env. clutter, but are separate PDFs in 85 Kr Detector components 9 0.07 10 − 6 the likelihood Plot for Background Energy Spectrum in inner 1T See talk by A. Cottle 0 50 100 150 200 approval Dispersed Radionuclides — Rn, Kr, Ar 819 — Electronic recoil energy [keV] “Backgrounds and Simulations for the LUX-ZEPLIN Experiment” Changes: thinner lines, moved labels, NR LZ Preliminary aspect ratio DM4 Mon afternoon 10 − 3 Laboratory and Cosmogenics 5 0.06 10 − 4 Rate [counts/kg/day/keV] ● DRU spectrum in inner 1T Surface Contamination and Dust 40 0.39 10 − 5 fiducial volume 8 B 10 − 6 14 Physics Backgrounds — 2 β decay, neutrinos* 322 0.51 Total Note: the 60 Co, 238 U, 232 Th spectra 10 − 7 Det. + Sur. + Env. hep from detector materials are 10 − 8 Total 1195 1.03 combined into ‘Detector’ to reduce 10 − 9 clutter, but are separate PDFs in 10 − 10 After 99.5% ER discrimination, 50% NR e ffi ciency 5.97 0.51 DSN A the likelihood t m 10 − 11 0 20 40 60 80 100 * not including 8 B and hep D.S. Akerib et al (LZ collaboration) 2018 arXiv:1802.06039 Nuclear recoil energy [keV] A. Fan (SLAC) TAUP2019 LZ Status 11 14