LUX results and LZ sensitivity to dark matter WIMPs Vitaly A. Kudryavtsev University of Sheffield for the LUX and LZ Collaborations Outline n Dark matter direct detection with two-phase noble element instruments. n LUX detector. n LUX results: o WIMPs – spin-independent interactions; o WIMPs – spin-dependent interactions; o Axions and axion-like particles (ALPs). o Modulation search. n LZ detector. n Backgrounds n Sensitivity to WIMPs. n Conclusions. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 2 Principle of WIMP detection in LXe TPC n Liquid xenon time projection chamber – LXe TPC. n S1 – primary scintillation. n S2 –secondary scintillation, proportional to ionisation. n Position reconstruction based on the light pattern in the PMTs and delay between S2 and S1. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 3 Advantages of LXe n Good scintillator. n Two-phase -> TPC with good position resolution. n Self-shielding. n Good discrimination between electron recoils (ERs) and nuclear recoils (NRs). n High atomic mass: spin-independent cross- section ∝ A2 n Presence of even-odd isotopes (odd number of neutrons) for spin-dependent studies. n Other physics: o Axion search, o Neutrinoless double-beta decay. LZ Collaboration, LZ TDR, 1703.09144v1 [physics.ins-det] ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 4 LUX Collaboration ² Brown University ² University at Albany, SUNY ² Imperial College London ² University College London ² LIP Coimbra, Portugal ² University of California, Berkeley ² Lawrence Berkley National Laboratory ² University of California, Davis ² Lawrence Livermore National Laboratory ² University of California, Santa Barbara ² Pennsylvania State University ² University of Edinburgh ² SLAC National Accelerator Laboratory ² University of Liverpool ² South Dakota School of Mines and ² University of Maryland Technology ² University of Massachusetts ² South Dakota Science and Technology ² University of Rochester Authority ² University of Sheffield ² Stanislaus State University ² University of South Dakota ² Texas A&M University ² University of Wisconsin – Madison ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 5 LUX detector § 61 top + 61 bottom ultra-low Thermosyphon background PMTs viewing ~250 kg LN bath of xenon in the active region (~120 column kg fiducial). Radiation shield § Ultra low background PMTs Titanium § Ultra-low background titanium vessels cryostat. Anode grid § Active region defined by high- PTFE reflector panels reflectivity PTFE walls. § Maximum drift: 50 cm. PMT holding 59 cm 49 cm copper plates § Xenon continuously re-circulated to maintain purity. Cathode grid § Chromatographic separation reduced Counterweight Kr content. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 6 LUX detector ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 7 LUX detector § 4850 ft level at SURF. Muon flux ~6×10-5 m-2 s-1. § Muon veto system and shielding: water tank instrumented with PMTs. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 8 LUX calibrations § 83mKr – uniform distribution, 1.8 hours half-life, weekly. § CH3T (tritiated methane) – uniform, removed by purification, 2-3 times a year (top figure), D. Akerib et al. (LUX Collaboration), Phys. Rev. D93 (2016) 072009. § D-D – generator (bottom), 2.45 MeV neutrons, collimated, D. Akerib et al. (LUX Collaboration), arXiv: 1608.05381 [physics.ins- det]. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 9 LUX results § Data after cuts: 332 live days (left). § Limits on spin-independent WIMP-nucleon cross-section (right); two runs combined: 2013 – 95 live days, 2015-2016 – 332 live days. Combined exposure 3.35×104 kg×days. § Limit 1.1×10-46 cm2 at 50 GeV/c2. § Akerib et al. (LUX Collaboration), PRL 118, 021303 (2017). ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 10 Most recent results § Most recent results from leading two-phase Xe experiments. § Plot from Aprile et al (XENON Collaboration). arXiv:1805.12562v1 [astro-ph.CO] ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 11 Spin dependent interactions § Spin-dependent WIMP-neutron cross-section (left): two Xe isotopes with odd number of neutrons. § Spin-dependent WIMP-proton cross-section (right): even number of protons. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 12 Axions and axion-like particles (ALPs) Axions ALPs -12 § LUX (2013) excludes gAe > 3.5×10 § LUX (2013) excludes -13 (90% CL). gAe > 4.2 × 10 (90% CL) across the 2 2 range 1-16 keV/c in ALP mass. • mA < 0.12 eV/c (DFSZ model). • m < 36.6 eV/c2 (KSVZ model). PRL 118, 261301 (2017) A Analysis of 2015-2016 data is in progress. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 13 Sensitivity to sub-GeV WIMPs n WIMP-nucleus interactions may result in the emission of bremsstrahlung photons by a polarised xenon atom. n Detection of these photons – improved sensitivity to low mass WIMPs (down to 0.3 GeV/c2). Currently preliminary results from 2013 data only; analysis of 2015-2016 data is ongoing. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 14 Modulation studies Diurnal (Preliminary) Annual (Preliminary) day/night: 2.28 / 2.36 cpd/keV/ton (siderial) Asymmetry: -1.7% ± 8.7% (stats only) ‘Signal’: 2-6 keVee A ≈ 0.5 cpd/keV/ton Φ ≈ 30 days since 1st Jan Control: 6-10 keVee A ≈ 0.12 cpd/keV/ton Φ ≈ 12 days since 1st Jan n The rate at low energies: ~2 events/ton/day/keV, 10-20 times lower than the DAMA modulation amplitude. n No statistically significant annual or diurnal modulation found. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 15 LUX-ZEPLIN (LZ) experiment ² Black Hills State University ² Brandeis University ² Brookhaven National Laboratory ² Brown University ² Center for Underground Physics, Korea ² Fermi National Accelerator Laboratory ² Imperial College London ² LIP Coimbra, Portugal ² Lawrence Berkley National Laboratory ² Lawrence Livermore National Laboratory ² MEPhl-Moscow, Russia ² Northwestern University ² Pennsylvania State University ² University of California, Santa Barbara ² Royal Holloway, University of London ² University of Edinburgh ² SLAC National Accelerator Laboratory ² University of Liverpool ² South Dakota School of Mines and Technology ² University of Maryland ² South Dakota Science and Technology Authority ² University of Michigan ² STFC Rutherford Appleton Laboratory ² University of Massachusetts ² Texas A&M University ² University of Oxford ² University at Albany, SUNY ² University of Rochester ² University College London ² University of Sheffield ² University of Alabama ² University of South Dakota ² University of Bristol ² University of Wisconsin – Madison ² University of California, Berkeley ² Washington University in St. Louis ² University of California, Davis ² Yale University ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 16 LZ detector LZ Collaboration, arXiv:1509.02910[physics.ins-det], 1703.09144v1 [physics.ins-det] 494 TPC-PMTs (253 top, 241 bottom) + 131 skin-PMTs LZ Collaboration, arXiv:1509.02910[physics.ins-det], 1703.09144v1 [physics.ins-det] Neutron calibration tube ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 17 LZ detector n From D. S. Akerib et al. (LZ Collaboration), arXiv: 1802.06039 [astro-ph.IM]. n 3’’ PMTs viewing the target volume. n 5.8 keV nuclear recoil energy threshold for 3-fold coincidences. n 0.31-0.65 kV/cm drift field, 99.5% ER/NR discrimination. n Max drift time ~0.8 ms defines the window for recording an event. n 5.6 t fiducial volume (to remove events from walls and wires). ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 18 Expected background From D. S. Akerib et al. (LZ Collaboration), arXiv:1802.06039. Planned live time 1000 days. Complementarity of high- sensitivity measurements of backgrounds (HPGe, ICPMS, radon measurements and control, neutron activation analysis) and accurate modelling of their effects in the detector (BACCARAT based on GEANT4 + NEST + detector response). ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 19 Background events n Single scatter nuclear recoil events in the LXe active volume before (left) and after (right) rejecting events in coincidence with veto system (LXe skin and the Outer Detector (OD). ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 20 Event spectra: ERs 1 10− Det. + Sur. + Env. 2 Total 10− 4 10− Total 3 10− 136 Xe 222Rn 4 10− 220 5 5 10− Solar 222 n 10− Rn Rn 220 85 Rn 6 10− Kr 136 Det. + Sur. + Env. Rate [counts/kg/day/keV] Rate [counts/kg/day/keV] Xe 7 85 10− Solar 6 Kr n 10− 8 10− 0 500 1000 1500 2000 2500 0 50 100 150 200 Electronic recoil energy [keV] Electronic recoil energy [keV] n Energy spectra of electron recoil background from various sources. n 222Rn dominates at low energies. n Environmental background and components are not major sources of background events. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 21 Event spectra: NRs 3 3 10− 10− 4 4 10− 10− 10 5 5 − 8B 10− 6 Total 6 8B 10− Det. + Sur. + Env. 10− hep 7 7 Total 10− 10− Det. + Sur. + Env. hep 8 8 10− 10− 9 9 Rate [counts/kg/day/keV] Rate [counts/kg/day/keV] 10− 10− 10 10 10− 10− DSN Atm DSN Atm 11 11 10− 10− 0 20 40 60 80 100 0 20 40 60 80 100 Nuclear recoil energy [keV] Nuclear recoil energy [keV] n Single scatter neutron recoil spectra before (left) and after (right) rejecting events coincident with veto systems. n The background rate is dominated by 8B solar neutrinos below 4 keV and atmospheric neutrinos above 4 keV (after cuts). n Surface contamination (from radon daughters) is another contributor. ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 22 WIMPs, 8B neutrinos and other backgrounds 5.0 n 8B events will limit the sensitivity to 4.5 low mass WIMPs. 4.0 [phd]) c 40 GeV (S2 10 3.5 log 3.0 8B + hep 2.5 0 10 20 30 40 50 60 70 80 S1c [phd] ICNFP2018, 6 July 2018 Vitaly Kudryavtsev 23 Sensitivity