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Paolo Beltrame University of Edinburgh (On Behalf of the LUX and LZ Collaborations)

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Paolo Beltrame University of Edinburgh (On Behalf of the LUX and LZ Collaborations) Recent results from LUX and status of LZ Paolo Beltrame University of Edinburgh (on behalf of the LUX and LZ collaborations) 51st Rencontres de Moriond Electro Weak and Unified Theories La Thuile, 12-19 March, 2016. 1 Outline • The Large Underground Xenon (LUX) experiment New results on WIMP searches and calibration • The LUX-ZEPLIN experiment Paolo Beltrame 2 Moriond EW 2016 Direct search Dark matter (DM) Milky Way’s halo => flux on Earth ~ 105 cm-2s-1 ρχ ~ 0.3 GeV/cm3 and 100 GeV/c2 Basic goal: search for nuclear recoil from DM elastic scattering. Simple dynamics: cross section ∝(form-factor)2 Spin-independent: nucleon form-factor gives rise to A2 enhancement due to coherence. The dependence on q2 is also contained in the form-factors. Spin-dependent: form-factor depends on nuclear spin. No coherence enhancement. Paolo Beltrame 3 Moriond EW 2016 LargeThe Underground LUX Collaboration Xenon Brown Collaboration Meeting, University at Albany, October 2015 SD School of Mines Richard Gaitskell PI, Professor Xinhua Bai PI, Professor Simon Fiorucci Research Associate Doug Tiedt Graduate Student Samuel Chung Chan Graduate Student Dongqing Huang Graduate Student Casey Rhyne Graduate Student SDSTA Will Taylor Graduate Student David Taylor Project Engineer James Verbus Graduate Student Mark Hanhardt Support Scientist Imperial College London Henrique Araujo PI, Reader Texas A&M Tim Sumner Professor Alastair Currie Postdoc James White † PI, Professor Adam Bailey Graduate Student Robert Webb PI, Professor Khadeeja Yazdani Graduate Student Rachel Mannino Graduate Student Paul Terman Graduate Student Lawrence Berkeley + UC Berkeley Bob Jacobsen PI, Professor University at Albany, SUNY Murdock Gilchriese Senior Scientist Kevin Lesko Senior Scientist Matthew Szydagis PI, Professor Peter Sorensen Scientist Jeremy Mock Postdoc Victor Gehman Scientist Sean Fallon Graduate Student Attila Dobi Postdoc Steven Young Graduate Student Daniel Hogan Graduate Student Mia Ihm Graduate Student UC Davis Kate Kamdin Graduate Student Kelsey Oliver-Mallory Graduate Student Mani Tripathi PI, Professor Lawrence Livermore John Thmpson Development Engineer Dave Hemer Senior Machinist Ray Gerhard Electronics Engineer Adam Bernstein PI, Leader of Adv. Detectors Grp. University of Edinburgh University of South Dakota Kareem Kazkaz Staff Physicist Aaron Manalaysay Scientist Brian Lenardo Graduate Student Jacob Cutter Graduate Student James Morad Graduate Student Alex Murphy PI, Reader Dongming Mei PI, Professor Paolo Beltrame Research Fellow LIP Coimbra Sergey Uvarov Graduate Student Chao Zhang Postdoc Tom Davison Graduate Student Angela Chiller Graduate Student Isabel Lopes PI, Professor Maria Francesca Marzioni Graduate Student Jose Pinto da Cunha Assistant Professor UC Santa Barbara Chris Chiller Graduate Student Vladimir Solovov Senior Researcher Francisco Neves Auxiliary Researcher Harry Nelson PI, Professor University of Maryland Yale Alexander Lindote Postdoc Mike Witherell Professor Susanne Kyre Engineer Claudio Silva Postdoc Carter Hall PI, Professor Daniel McKinsey PI, Professor Dean White Engineer SLAC Nation Accelerator Laboratory Jon Balajthy Graduate Student Ethan Bernard Research Scientist Carmen Carmona Postdoc Richard Knoche Graduate Student Markus Horn Research Scientist Scott Haselschwardt Graduate Student Dan Akerib PI, Professor Blair Edwards Postdoc Thomas Shutt PI, Professor Curt Nehrkorn Graduate Student University of Rochester Scott Hertel Postdoc Kim Palladino Project Scientist Melih Solmaz Graduate Student Kevin O’Sullivan Postdoc Tomasz Biesiadzinski Research Associate Frank Wolfs PI, Professor Elizabeth Boulton Graduate Student Christina Ignarra Research Associate University College London Wojtek Skutski Senior Scientist Nicole Larsen Graduate Student Wing To Research Associate Eryk Druszkiewicz Graduate Student Rosie Bramante Graduate Student Chamkaur Ghag PI, Lecturer Evan Pease Graduate Student Wei Ji Graduate Student James Dobson Postdoc Dev Ashish Khaitan Graduate Student Brian Tennyson Graduate Student T.J. Whitis Graduate Student Sally Shaw Graduate Student Mongkol Moongweluwan Graduate Student Lucie Tvrznikova Graduate Student Paolo Beltrame 4 Moriond EW 2016 LUX detector • Davis Cavern @ Sanford Lab (SURF), 4850 ft (1.5 km) underground • 250 kg (47 x 49 cm2) of active LXe dual phase time projection chamber (TPC) log10(cts/kg/day/keV) • Two arrays each of 61 ultra-pure PMTs • Reducing background: • cosmic μ flux reduced to 6.2 × 10−9 cm−2s−1 • low background materials • 3D event localisation (LXe target fiducialization) Paolo Beltrame 5 Moriond EW 2016 S1, S2 and CES Liquid xenon / dual-phase time projection chamber (TPC) (Ionisation) S2 1 μs ‘Combined Energy scale’ 1 S1 S2 E = + W L(E) · g g · ✓ 1 2 ◆ (Scintillation) S1 • W = 13.7 eV • g1 = Light Collection • g2 = Extraction + Light Eff. 100 ns • L(E) = Lindhard Factor Nuclear recoil enhancement of heat relative to electron recoils Paolo Beltrame 6 Moriond EW 2016 Nuclear vs. Electron recoil Combination of Scintillation (S1) and Ionisation (S2) event-by-event particle identification Electron Recoil (ER) events 4 Nuclear Recoil (NR) events 2.5 ER(a) Tritium calibration ER Calibration data TABLE I. Predicted background rates in the fiducial volume 2 (0.9–5.3 keVee) [31]. We show contributions from the γ- rays of detector components (including those cosmogenically 1.5 activated), the time-weighted contribution of activated xenon, 222Rn (best estimate 0.2 mDRUee from 222Rn chain 1 0.4 measurements) and 85Kr. The errors shown are both keV ee 0.8 1.3 1.8 2.4 2.9 3.5 4.1 4.6 from simulation statistics and those derived from the rate 2.5 measurements of time-dependent backgrounds. 1 mDRUee is (S2/S1) (b) AmBe and Cf−252 NR Calibration /S1) x,y,z corrected b 3 10 NR calibration data 2 10− events/keVee/kg/day. (S2 log 10 Source Background rate, mDRUee 1.5 log γ-rays 1.8 0.2stat 0.3sys 127 ± ± Xe 0.5 0.02stat 0.1sys 1 3 214 ± ± keV 6 9 12 15 18 21 24 27 Pb 0.11–0.22 (90% C. L.) nr 85 Kr 0.13 0.07sys 0 10 20 30 40 50 ± S1 x,y,z corrected (phe) Total predicted 2.6 0.2stat 0.4sys S1 ± ± Total observed 3.1 0.2stat Paolo Beltrame FIG. 3. Calibrations7 of detector response in theMoriond 118 kg fiducialEW 2016 ± volume. The ER (tritium, panel a) and NR (AmBe and 252Cf, panel b) calibrations are depicted, with the means (solid line) Facility (SOLO) and the LBNL low-background counting and 1.28σ from Gaussian fits to slices in S1 (dashed line). This± choice of band width (indicating 10% band tails) is for facility [13, 26, 32]. Krypton as a mass fraction of xenon presentation only. Panel a shows fits to the high statistics was reduced from 130 ppb in the purchased xenon to tritium data, with fits to simulated NR data shown in panel 4 ppt using gas charcoal chromatography [33]. b, representing the parameterizations taken forward to the Radiogenic backgrounds were extensively modeled profile likelihood analysis. The ER plot also shows the NR using LUXSim, with approximately 80% of the low- band mean and vice versa. Gray contours indicate constant energy γ-ray background originating from the materials energies using an S1–S2 combined energy scale (same contours in the R8778 PMTs and the rest from other construction on each plot). The dot-dashed magenta line delineates the materials. This demonstrated consistency between the approximate location of the minimum S2 cut. observed γ-ray energy spectra and position distribu- tion [31], and the expectations based on the screening results and the independent assay of the natural Kr calibrations therefore include systematic e↵ects not concentration of 3.5 1 ppt (g/g) in the xenon gas [34] where we assume an± isotopic abundance of 85Kr/natKr applicable to the WIMP signal model, such as multiple- 11 scattering events (including those where scatters occur 2 10− [31]. Isotopes created through cosmogenic ⇠production⇥ were also considered, including measured in regions of di↵ering field) or coincident Compton 60 scatters from AmBe and 252Cf γ-rays and (n,γ) reactions. levels of Co in Cu components. In situ measurements These e↵ects produce the dispersion observed in data, determined additional intrinsic background levels in xenon from 214Pb (from the 222Rn decay chain), and which is well modeled in our simulations (in both 127 band mean and width, verifying the simulated energy cosmogenically-produced Xe (T1/2 = 36.4 days), 129m 131m resolution), and larger than that expected from WIMP Xe (T1/2 =8.9 days), and Xe (T1/2 = scattering. Consequently, these data cannot be used 11.9 days). The rate from 127Xe in the WIMP search directly to model a signal distribution. For di↵erent energy window is estimated to decay from 0.87 mDRUee WIMP masses, simulated S1 and S2 distributions are at the start of the WIMP search dataset to 0.28 mDRUee obtained, accounting for their unique energy spectra. at the end, with late-time background measurements The ratio of keVee to nuclear recoil energy (keVnr) being consistent with those originating primarily from relies on both S1 and S2, using the conservative technique the long-lived radioisotopes. presented in [29] (Lindhard with k =0.11). NR data Neutron backgrounds in LUX were constrained by are consistent with an energy-dependent, non-monotonic multiple-scatter analysis, with a conservative 90% upper reduced light yield with respect to zero field [30] with C.L. placed on the number of expected neutron single a minimum of 0.77 and a maximum of 0.82 in the scatters with S1 between 2 and 30 phe of 0.37 in range 3–25 keVnr [23]. This is understood to stem from the 85.3 live-day dataset, with simulations predicting a additional, anti-correlated portioning into the ionization considerably lower value of 0.06 events. channel. We observed 160 events between 2 and 30 phe (S1) The observed ER background in the range 0.9– within the fiducial volume in 85.3 live-days of search 5.3 keV within the fiducial volume was 3.1 data (shown in Fig.
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