Do WIMPs Rule? The LUX & LZ Experiments and the Search for Cosmic Dark Matter

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1 Do WIMPs Rule? The LUX & LZ Experiments and the Search for Cosmic Dark Matter!" Dan Akerib! SLAC National Accelerator Laboratory Kavli Insitute for Particle Astrophysics & Cosmology

2 Standard cosmology: An inventory of the universe SDSS-III / BOSS from Perlmutter, Phys. Today (units of critical density) supernovae Energy density Baryon acoustic oscillations Matter density 3 Kelvin cosmic microwave background WMAP WMAP Tytler & Burles

3 WIMP Hypothesis Early Universe as Particle Factory Not enough protons and neutrons produced in the Big Bang Convert energy to mass E=mc 2 quark WIMP distance anti-quark anti-wimp A new type of particle: WIMPs = weakly interacting massive particles Massive: source of gravity Weakly-interacting: not star forming time

4 cross section annihilation rate

5 cross section annihilation rate

6 WIMP freezeout WIMP pairs produced in equilibrium Annihilation stops when number density falls too low H > Γ A ~ n χ σ A v Production = Annihilation (T m χ ) Production suppressed (T<m χ ) Freeze out annihilation rate slower than Hubble expansion ( freeze out ) mean free time > age For Ω χ 1 M GeV σ A electroweak SUSY/LSP? Comoving Number Density ~exp(-m/t) Jungman, Greist, Kamionkowski m χ / T (time )

7 Dark Matter in Galactic Halos data with dark halo if only stars and gas Vera Rubin and Kent Ford, 1978

8 Scattering experiment WIMP WIMPs/year density, speed dark matter halo light years 1 light year Cross section: WIMP scatters once in a light year of lead detector Rate ~ few events / year

9 WIMP search - c.1988: converted neutrino detector Germanium ionization detector at the Oroville Dam, CA searching for double beta decay - progenitor to Majorana Event rate ruled out heavy neutrinos as DM Recoil energy transfer to nucleus from Jungman et al. (D.O. Caldwell et al.)

10 WIMP search - c.1988: converted neutrino detector Germanium ionization detector at the Oroville Dam, CA searching for double beta decay - progenitor to Majorana Event rate log cross section (arb. units) Gaitskell,Mandic,Filippini WIMP Mass [GeV] Recoil energy transfer to nucleus from Jungman et al. (D.O. Caldwell et al.)

11 Energy deposition WIMP 10% energy Ionization Phonons/heat 100% energy slowest cryogenics Light 1% energy fastest no surface effects

12 An active field with many approaches! WIMP CoGent (HPGe) DMTPC (gas dir.) DRIFT (gas dir.) 2-phase nobles: ZEPLIN, XENON, WARP, LUX/LZ, ArDM, Darkside 10% energy Ionization Semiconducting calorimeters: CDMS, Edelweiss Superheated liquids: Picasso, Simple, Coupp, PICO Phonons/heat 100% energy slowest Inorganic scintillators: DAMA/LIBRA, KIMS Single-phase liquid nobles: DEAP, MiniCLEAN, XMASS Light 1% energy fastest CRESST II low radioactivity background immunity large mass / stable operation shielded low energy threshold

13 Water, 2.6 MeV gammas Shielding Gamma Rays Water 1 m water shielding Liquid Xe, 2.6 MeV gammas Liquid Xenon 1 m liquid Xe

14 The Large Underground Xenon Detector 250 kg active 170 K S1, S2 event energy S2 event xy location S1-S2 timing z location S2/S1 recoil type z y x

15 Inside the LUX/LZ water tank Sanford Underground Research Facility 4850-foot deep Davis Cavern Homestake Gold Mine Lead, SD The LUX Experiment photo credits: Matt Kapust, SURF

16 Former Homestake Gold Mine Sanford Underground Research Facility

17 Backgrounds: neutrons cosmic ray muons Gammas in Water muons down by 10,000,000x neutron scatter nuclear disintegration neutron moderated by water shield photo credit: Matt Kapust, Sanford Lab

18 1964 Nov

19 Internal dangers: radioactive 85 Kr 10-y T 1/2 beta decay Can t self-shield Noble gas: non-reactive ~130 ppb in purchased Xe LUX background floor from 122 PMTs ~ 20 ppt Kr/Xe ν e - 85 Kr 85 Rb + e - + ν e - Kr Xe Chromatography He gamma ray

20 Gas charcoal chromatography Kr removal Kr Xe He

21 400 kg Xe at Case: 130 ppb to 4 ppt thermosyphon dewar traps thermosyphon lines (3) charcoal column condenser gas panel gas control panel Xe recovery pumps sampling RGA graduate student Chang Lee feed & recovery bottles arxi C. Hall, UMD: Assay with ppt sensitivity

22 50 kg / week processed for LUX Xe partial pressure Xe feed (mass) (arb units) 45 kg 4 days

23 Raw signals in LUX Depth from timing difference z y x Lateral location from top PMT Array

24 Signal production in liquid Xe e - E ~ kev Xe Xe + Ion Xe2 + Ionized molecule e - e - e - S2 Recombination Xe Xe Heat Xe Xe* Excitation Xe2* VUV photon, 175nm S1 Electron Recoils

25 Signal production in liquid Xe Xe E ~ kev Xe Xe + Ion Xe2 + Ionized molecule e - e - e - S2 Recombination Xe Xe Heat Xe Xe* Excitation Xe2* VUV photon, 175nm S1 Nuclear Recoils

26 Understanding light and charge Electric Field Electron recoils Nuclear recoils Puzzling low energy behavior Comprehensive model, only 2 fit parameters (Dahl, PhD thesis, 2009) Robust Monte Carlo framework: NEST (M. Szydagis et al., JINST 6, p10002 (2011))

27 Background and Signal Distinction Background in situ LUX calibrations More charge, less light Signal τ Internal tritium source (purified away with ~ 7 hours)

28 WIMP signal Signal region: a quiet place where low-energy singlescatter nuclear recoils away from the walls can emerge from among: external gamma rays into the fiducial volume wall events (206Pb) dissolved backgrounds (Rn-progeny, 85Kr, 127Xe) delayed electrons from previous large S2 s amplitude (phe/10 ns) S1 summed across all channels ALPHA POPULATIONS IN XY amplitude (phe/10ns) PMT channel ALPHA POPULATIONS IN number R Z time (µs) time (µs) m Kr injection movie 550 sec 83m Kr injection movie 550 sec

29 0.6 Event selection S1 summed across all channels S2 summed across all channels amplitude (phe/10 ns) amplitude (phe/10 ns) amplitude (phe/10ns) time (µs) S time (µs) S time (µs) 0 PMT channel number Requirements for WIMP search candidate events S2 trigger (at least 2 trigger ch. 8 phe within 2 µs) [lower threshold than S1] 2 phe (2-fold coincidence) S1 30 phe [quiet enough to see this in look back ] 200 phe (8 e-) S phe [require good xy measurement] total area of other pulses in the event < 100 phe [confusion from previous large S2's]

30 LUX WIMP Search, 85 live-days, 118 kg calibration kev ee 1.8 ER Calibration 99.6±0.1% leakage below NR mean, so expect / for 160 events log (S2 /S1) x,y,z corrected 10 b kevnr S1 x,y,z corrected (phe) gate grid drift time (µs) wall face wall corner 350 cathode grid radius 2 (cm 2 ) 160 events in ER band / 118 kg fiducial

31 Extended Likelihood Treatment Observables: x = (S1, log 10 (S2/S1), r, z) Parameter of interest: Nuisance parameters: N s N Compt, N Xe-127, N Rn/Kr-85 Modeled WIMP signal, including resolution and efficiencies 8 GeV /c 2 WIMP 100 GeV /c 2 WIMP 2 TeV /c 2 WIMP

32 Spin Independent Cross Section Upper Limit WIMP nucleon cross section (cm 2 ) ZEPLIN III Edelweiss II CDMS II Ge XENON100(2011)-100 live days XENON100(2012)-225 live days LUX (2013)-85 live days LUX +/-1σ expected sensitivity m (GeV/c ) WIMP Phys. Rev. Lett. 112, (2014)

33 Spin Independent Cross Section Upper Limit WIMP nucleon cross section (cm 2 ) m WIMP (GeV/c )

34 Low Mass WIMPs CDMS II Ge WIMP nucleon cross section (cm 2 ) DAMA/LIBRA Favored CoGeNT Favored x CDMS II Si Favored XENON100(2012) 225 live days CRESST Favored LUX (2013) -85 live days m WIMP (GeV/c 2 ) w/newest CDMS result

35 Next for LUX WIMP nucleon cross section (cm 2 ) DAMA/LIBRA CoGeNT (2012) CDMS II Si (2013) CRESST II ZEPLIN III XENON m (GeV/c ) WIMP CDMS II Ge LUX 85d (2013) Projected LUX 300 day run ( ) Updated analysis of 85d - improved reconstruction - lower threshold - wall distribution into PLR? - complete DD calibration - NEST update! 300d run: above + - improved extraction field Xe decayed away

36 LZ: LUX + ZEPLIN 20-fold scale-up from LUX Two-component outer detector system 0.75 m thick Gd-loaded LAB scintillator shield (c.f.: Daya Bay) Instrumented Xe skin Effective for neutrons and gammas HV water shield scintillator detector 7 ton LXe TPC fits in Davis Cavern

37 LZ Reach and Snowmass WIMP nucleon cross section cm Be Neutrinos SuperCDMS PICO250-C3F8 CDMSlite (2013) SNOLAB NEUTRINO C OHER ENT SCATTERING 8 B Neutrinos (Green&ovals)&Asymmetric&DM&& (Violet&oval)&Magne7c&DM& (Blue&oval)&Extra&dimensions&& (Red&circle)&SUSY&MSSM& &&&&&MSSM:&Pure&Higgsino&& &&&&&MSSM:&A&funnel& &&&&&MSSM:&BinoEstop&coannihila7on& &&&&&MSSM:&BinoEsquark&coannihila7on& & SuperCDMS Soudan Low Threshold XENON 10 S2 (2013) CDMS-II Ge Low Threshold (2011) CoGeNT (2012) CRESST Updated from Snowmass Community Summer Study 2013 CF1: WIMP Dark Matter Detection CDMS Si (2013) DAMA EDELWEISS (2011) DEAP WIMP Mass GeV c 2 SIMPLE (2012) SuperCDMS Soudan LUX 300-day SuperCDMS SNOLAB NEUTRINO COHERENT SCATTERING Atmospheric and DSNB Neutrinos COUPP (2012) ZEPLIN-III (2012) CDMS II Ge (2009) Xenon100 (2012) LUX (2013) DarkSide 50 PICO250-CF3I Xenon1T DarkSide G2 LZ WIMP nucleon cross section pb 3 year run, limited primarily by (electron recoil) background of pp solar neutrinos limited by nuclear scatter background? reach to cm 2 neutrino floor depends on rejecting pp solar

38 Lab Activities at SLAC Fundamental measurements Test platform for LZ prototyping and long-term R&D 45 cm 80 cm Purification Tower Test TPC in 100 kg 170 K LXe vessels w/200 kv feedthrough ports for LZ system test HV feedthrough (drift field) Removal of trace radioactive 85 Kr thermosyphon w/gas dewar charcoal chromatography high-flow pneumatically controlled Xe circulation & purification panel thermosyphon lines (3) charcoal column Xe recovery pumps condenser sampling RGA graduate student gas control panel feed & recovery bottles

39 Former BaBar IR2 complex Repurposed electronics hut: LZ / liquid nobles test stand LSST Clean Room pump shed Xe storage

40 LZ / liquid nobles test stand LN thermosyphon and controls Phase I & II system test Re-furbished LUX Kr removal for R&D

41 Kr removal: reduction to ppt ~ 10% pp solar ν 10 tons / kg/day X 2 passes 500 mbar 500 SLPM He (Fluitron compressor) 16 kg 250 SLPM He (dry backing pump) 100 mbar thermosyphon Xe charcoal 500 kg LN cryocooler cooled Kr trap Xe/Kr chromatography filter 10 mbar 250 SLPM He (Roots booster) U sampling RGA 50 SLPM Xe 2 bar 80 bar Xe storage He feed/purge ~ 120 min Xe recovery Xe ~ 120 min condensers 200 kg capacity 24 hour cycle (per condenser) automation of all 3 cycles

42 Dark matter detection - exciting future Liquid xenon TPCs playing key role 300-day data set for LUX ~ 4-5x LZ approaches neutrino floor Summary WIMP nucleon cross section cm 2 WIMP nucleon cross section (cm 2 ) Be Neutrinos PICO250-C3F8 SuperCDMS SNOLAB NEUTRINO C OHER ENT SCATTERING SuperCDMS Soudan CDMS-lite SuperCDMS Soudan Low Threshold XENON 10 S2 (2013) CDMS-II Ge Low Threshold (2011) 8 B Neutrinos (Green&ovals)&Asymmetric&DM&& (Violet&oval)&Magne7c&DM& (Blue&oval)&Extra&dimensions&& (Red&circle)&SUSY&MSSM& &&&&&MSSM:&Pure&Higgsino&& &&&&&MSSM:&A&funnel& &&&&&MSSM:&BinoEstop&coannihila7on& &&&&&MSSM:&BinoEsquark&coannihila7on& & CoGeNT (2012) CRESST CDMS Si (2013) DAMA EDELWEISS (2011) WIMP Mass GeV c 2 SIMPLE (2012) NEUTRINO COHERENT SCATTERING Atmospheric and DSNB Neutrinos m WIMP (GeV/c ) COUPP (2012) ZEPLIN-III (2012) CDMS II Ge (2009) SuperCDMS Soudan Xenon100 (2012) DarkSide 50 LUX Xenon1T DarkSide G2 DEAP3600 PICO250-CF3I LZ WIMP nucleon cross section pb

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