Direct Detection of Dark Matter with LUX we are a collaboration of 50+ scientists, please see http://lux.brown.edu for more information Peter Sorensen Lawrence Livermore National Laboratory DNP October Meeting 2009 1
DNP October Meeting 2009 2 Scope of Talk 1. LUX goal: direct detection of dark matter. case for dark matter predicted event rates (vanilla model) current and future sensitivities 2. Managing backgrounds External Internal (dominant) 3. Dual phase liquid xenon TPC typical events discrimination of ER (background) from NR (signal) 4. Other models of dark matter (idm) In brief: LUX is a 300 kg liquid xenon TPC viewed by 122 PMTs
LUX Goal: Direct Detection of Dark Matter (below) galactic mass density profile obtained from combined (weak + strong) lensing observations of 22 galaxies we are here WMAP 5-year data (2008) gives matter densities (Ω) based on best fit to Λ-CDM cosmological model: Ω total = 1.02 ± 0.02 Ω c = 0.233 ± 0.013 Ω b = 0.0462 ± 0.0015 Ω Λ = 0.721 ± 0.015 Ω ν < 0.0076 H0 = 70.1 ± 1.3 km s -1 Mpc -1 Assuming Ω c is composed of Weakly Interacting Massive Particles (WIMPs): Dark matter particles by definition do not interact electromagnetically, and so should scatter preferentially from nuclei relic density of ~3 WIMPs / liter: (Mx = 100 GeV/c 2 ) DNP October Meeting 2009 3
Predicted Event Rates elastic WIMP-nucleus scattering: Lewin and Smith, Asropart. Phys. 6 87 (1996) A 2 coherence for spin-independent dn/de nr [ kevr!1 kg!1 d!1 ] 10!2 10!3 10!4 10!5 10!6! "!n =1 10!45 cm 2 m " = 100 GeV 5 kev threshold, 300 live days, 100 kg target => 18 events (~ 7 events after cuts) 0 10 20 30 40 50 60 70 Nuclear Recoil Energy [kevr] Xe elastic scatters integrated rate above energy threshold LUX # background before discimination LUX # background after discimination < 1 ER background event 5-25 kevr, after discrimination DNP October Meeting 2009 4
Dark Matter Direct Detection (State of the Art) Building on established technology: XENON10 (2007) Exposure: 5.4 kg fiducial, 58 days live (BG limited) Sensitivity (100 GeV WIMP): 8.8x10-44 cm 2 (<1 evt/kg/month) LUX (2010) discovery potential! Exposure: 100 kg fiducial, 300 days live Project >10 4 kg-days after cuts/nr acceptance Sensitivity (100 GeV WIMP): 7x10-46 cm 2 (<0.5 evt/100 kg/month) Comparison: SuperCDMS (2013) Goal @ SNOLab: Gross Ge Mass 25 kg (x 50% fid mass+cut acceptance) Limit set for 1000 days live x 7 SuperTowers Cross-section [cm 2 ] (normalised to nucleon) 10-41 10-42 10-43 10-44 10-45 10-46 This plot has a limited number of current and projected results. Please see http://dmtools.brown.edu LUX (2010) 080311132601 ZEPLIN II WIMP Mass [GeV/c 2 ] http://dmtools.brown.edu/ Gaitskell,Mandic,Filippini Edelweiss I CDMS II (2006) WARP XENON10 (2007) CDMS II@Soudan (2006+2008) XMASS (2009?) SuperCDMS@SNOLab (2013) 10 1 10 2 10 3 How will LUX achieve this level of sensitivity? DNP October Meeting 2009 5
DNP October Meeting 2009 6 Primary Challenge: Manage Backgrounds ^assuming everything else works perfectly Table assumes 100 kg fiducial mass, 300 days live expect 2 BG events in 300 days live conservative! ER background goal (before discrimination)
Reduction of External Background 300 tonnes H2O shielding 3.5 meter thickness (radial) 20 tonnes inverted steel pyramid (underneath) Background flux reduction study (below) by L. deviveiros (Brown U.) External background << Internal background Peter Sorensen, LLNL 7 snowpac, 2-6 February 2009
DNP October Meeting 2009 8 Internal Backgrounds (γ) applecu: 10 ppt U / 12 ppt Th / 18 ppb K [~1% of total ER BG budget] Cosmogenic activation of Cu (sea-level: 2.1 mbq/kg 60Co would be ~43% of ER BG budget) need to limit surface exposure to < 12 months appleteflon: < 13 ppt U / < 39 ppt Th / 22 ppb K [~1% of total ER BG budget] XENON10 upper limits x10 lower U/Th EXO measured x1000 lower appleti: <1 mbq/kg for grade CP1. Some 46 Sc activity, but has only 86 day t1/2. applepmts: Dominant source of ER BG: activities ~ x10 3 higher (per unit mass) calcs and Monte Carlo assume: U/Th/K/Co 18/17/30/8 (mbq/pmt). All PMTs surveyed so far have shown lower values [cm] -60-50 -40-30 -20-10 0 log10(dru) -20-10 0 10 20 [cm] above: Monte Carlo of (dominant) PMT activity in LUX Goal
DNP October Meeting 2009 9 Internal Backgrounds (neutron) PMTs are the primary (internal) source of neutron background: apple fission [~1.5% of goal, > 6 MeV prompt γ ] apple (α,n) [higher yield for lighter elements] Calcs assume U/Th/K/Co = 18/17/30/8 (mbq/pmt) apple=> 1.5 neutrons / yr / PMT applemonte Carlo assumes 5 neutrons / yr / PMT (very conservative) NOTE: Teflon (α,n) sub-dominant (10% of goal) assuming EXO measurements for U/Th [cm] -60-50 -40-30 -20-10 0 log10(dru) -20-10 0 10 20 [cm] Goal x20 reduction in FV with multiple scatter veto
Other Potential Intrinsic Backgrounds Potential sources of radioactivity that could be dissolved/contained in Xe / detector components: applexe is clean! apple 85 Kr (τ 1/2 = 10 y) => reduced to < 2 ppt by CWRU charcoal column [2 ppt => ~0.4 μbq/kg => 0.8x10-4 dru], ~10% of ER BG budget... but also an upper limit appleu/th => materials selected for U/Th safely below targets applern => need to worry about Rn (next slide) appleatmospheric gases => H2O, CH4, CO2... removed by high T getter 3 H 14 C}naked β emitters. H,C removed by getter. materials selected for low 40 K. 40 K applecosmogenic activation of Xe sub-dominant for any reasonable surface exposure (τ 1/2 ~ 10 days) External backgrounds which are sub-dominant (dru rates quoted for 0-50 kevee): applep-p solar ν => ~1.2x10-5 dru [~1.5% of LUX bg goal] apple 136 Xe ββ => current limit τ 1/2 = 0.8x10 22 would give ~3x10-6 dru [0.3% of LUX bg goal] apple Thermal neutron radiative capture on Xe => several coincident γ s (~7 MeV) NOTE: assessments conservatively assume ER rejection is only 99.4% DNP October Meeting 2009 10
LUX Detector (everything else, working perfectly) LUX: 300 kg total (100 kg target) xenon target: 60 cm height, 50 cm diam. preparing for installation at DUSEL (Homestake, SD) 6 m diam. H2O shield Peter Sorensen, LLNL 11 snowpac, 2-6 February 2009
Typical Signals in LUX microseconds DNP October Meeting 2009 12
Discrimination in Xe: Electron Recoil vs Nuclear Recoil ~4 kevr single scatter nuclear recoil 18 data from XENON10 16 50% acceptance 14 12 3.6 phe 595 phe phe/sample 10 8 6 phe x10 S1 S2 neutrons γ,β 13-17 kevr 4 2! 0.10 µs " 0 3.5 3 45 50 55 60 65 70 75 80 85 µs 137 Cs AmBe!)*+)"!(),-).//01+*2/0)! #!!$ &&'!( log 10 (S2/S1) 2.5 γ,β 6-)-070/+892 &&'"( 2 neutrons #!!% &&'&( 1.5 0 10 20 30 40! " #! #" $! $" %! %" kev 3045 r [QF=0.19] DNP October Meeting 2009 13
Slight dulling of Occam s Razor in brief: Inelastic Dark Matter D Tucker-Smith and N Weiner, Phys Rev D 72 063509 (2005) consequences: elastic predicted rates in Ge for MX = 100 GeV compatible with DAMA modulation signal and null results from CDMS / XENON10! inelastic Nuclear Recoil Energy Peter Sorensen, LLNL 14 snowpac, 2-6 February 2009
idm Allowed Parameter Space S Chang, G Kribs, D Tucker-Smith and N Weiner, Phys Rev D 79 043513 (2009) DNP October Meeting 2009 15
DNP October Meeting 2009 16 Update from XENON10 0 # (1(#2"(3+, #"!&! +4/567+7 ". (((((((((()/0 $ - #"!&' #"!%" idm is still a viable explanation of the DAMA modulation signal #"!%# 8559:+7!" #"" #$" #%"!(((((((((()*+,- (preprint will be on arxiv shortly)
LUX idm Sensitivity after 1 Month Live dn/de nr [ kevr 1 kg 1 d 1 ]! " n =1 10 40 cm 2 m " = 150 GeV # = 120 kev 10 2 10 3 10 4 10 5 10 6 0 10 20 30 40 50 60 70 80 90100 Nuclear Recoil Energy [kevr] expect 17 events in 1 month after background discrimination and all cuts idm on xenon target (winter) idm on xenon target (summer) LUX $ background before discimination LUX $ background after discimination => confirm or rule out idm interpretation of DAMA modulation summer 2010 DNP October Meeting 2009 17
Summary 1.LUX 300 kg (100 kg fiducial) Xe detector will build on established Xe technology 2.Conservative assumption of 99.4% ER versus NR discrimination 3.Conservative BG model predicts 1 ER and 1 NR event in signal window, for 100 kg fiducial and 300 days live 4.Expect sensitivity to (100 GeV) WIMP dark matter of 7x10-46 cm 2 (interaction rate ~ 4 events in 100 kg target in 300 days live) x100 below current exclusion limits discovery potential 5.Confirm or Rule out idm interpretation of DAMA modulation in 1 month live 6.Installation at DUSEL (Homestake) Sanford Lab 4850ft in Winter 2010. ^Deep Underground Science and Engineering Laboratory DNP October Meeting 2009 18
Mahalo DNP October Meeting 2009 19