Direct Detection: Liquid Nobles

Transcription

1 Direct Detection: Liquid Nobles Dan Akerib SLAC National Accelerator Lab and Kavli Institute for Particle Astrophysics and Cosmology Stanford University LUX / LZ collaborations! 9 September 2015

2 WIMPs in the Galactic Halo! data bulge, disk & halo bulge & disk sun halo bulge disk Scatter from a Nucleus in a Terrestrial Particle Detector Log(rate) E ~ 30 kev The Milky Way E recoil

3 Backgrounds: cosmic rays and natural radioactivity WIMP scatters (< 1 evts /0 kg/ 0 day) swamped by backgrounds ( > 6-7 evts/kg-d) Radioactive Nuclides in rock, surroundings 238 U, 232 Th chains, 40 K, 39, 85 Kr (α, n) Airborne Radioactivity 222 Rn Spontaneous fission Shield contaminants Electrons Radioactive Nuclides in detector, shield Gammas Neutron capture Cosmic Rays Radioactive Nuclides in atmosphere (α, n) Photo fission Fast muons Slow muons Muon capture courtesy of S. Kamat Neutrons

4 Minimizing backgrounds Critical aspect of any rare event search Purity of materials Copper, germanium, xenon, neon, water among the cleanest with no naturally occurring long-lived isotopes Lead if free of 2 Pb (T 1/2 = 22 years) Shielding/vetoing Underground siting Radon mitigation Material handling surface preparation activation from cosmic rays Assay techniques Detector-based discrimination log(sensitivity) Discovery: understand residual background bkg free: ~t bkg: ~t 1/2 systematics log(exposure)

5 Energy deposition WIMP % energy Ionization Phonons/heat 0% energy slowest cryogenics Light 1% energy fastest no surface effects

6 An active field with many approaches! WIMP CoGent (HPGe) DMTPC (gas dir.) DRIFT (gas dir.) 2-phase nobles: ZEPLIN, XENON, WARP, LUX/LZ, DM, Darkside Ionization % energy Semiconducting calorimeters: CDMS, Edelweiss Phonons/heat Superheated liquids: Picasso, Simple, Coupp, PICO 0% energy slowest Inorganic scintillators: DAMA/LIBRA, KIMS Light 1% energy fastest CRESST II Single-phase liquid nobles: DEAP, MiniCLEAN, XMASS

7 An active field with many approaches! WIMP CoGent (HPGe) DMTPC (gas dir.) DRIFT (gas dir.) 2-phase nobles: ZEPLIN, XENON, WARP, LUX/LZ, DM, Darkside Ionization % energy Semiconducting calorimeters: CDMS, Edelweiss Phonons/heat Superheated liquids: Picasso, Simple, Coupp, PICO 0% 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 cost

8 Xenon, electron recoil Signal production in liquid nobles Xe Xe + Ion Xe2 + Ionized molecule e - e - e - S2 Recombination Xe Xe VUV photons 175nm Xe* Xe2* Heat Xe Excitation S1 Branching ( ) sketched for electron recoils diagram - T. Shutt

9 Xenon, nuclear recoil Signal production in liquid nobles Xe Xe + Ion Xe2 + Ionized molecule e - e - e - S2 Recombination Xe Xe VUV photons 175nm Xe* Xe2* Heat Xe Excitation S1 Branching ( ) sketched for nuclear recoils diagram - T. Shutt

10 gon, electron recoil Signal production in liquid nobles + Ion * 2 + Ionized molecule e - e - e - S2 Recombination 2* singlet, 7ns S1 (Fast) Heat Excitation triplet, 1.6us S1 (Slow) Branching ( ) sketched for electron recoils

11 gon, nuclear recoil Signal production in liquid nobles + Ion * 2 + Ionized molecule e - e - e - S2 Recombination 2* singlet, 7ns S1 (Fast) Heat Excitation triplet, 1.6us S1 (Slow) Branching ( ) sketched for nuclear recoils

12 Basic properties of liquid noble detectors VUV to EUV - challenging but not impossible for PMTs Long attenuation length - nominally transparent; depends on impurities Long charge drift length - but requires significant engineering for purification and high voltage Good dielectric / cryo environment nice for PMTs Low-background artisanal PMTs - steadily improved by Hamammatsu Differential response for ER vs NR Pulse Shape Discrimination (PSD) and S2/S1

13 single phase / dual phase 4π Scintillation Time Projection Chambers (TPC)

14 Single Phase Dual Phase DEAP MiniCLEAN DarkSide DM XMASS LUX/LZ XENON-0/1T/nT Panda-X discharge tubes from

15 two-phase LXe

16 TPC signals Depth from timing difference z y x ateral location from top PMT ray

17 TPC signals Depth from timing difference z y x ateral location from top PMT ray

18 LXe TPC experiments LUX XENON-0 LUX Panda-X

19 !" LUX WIMP Search, 85 live-days, 118 kg Carlos Hernandez Faham Brown University LUX Collaboration Meeting October 22, 2011 calibrations kev eeer Calibration 99.6±0.1% leakage below NR mean, so expect / for 160 events 1.8 log (S2 b /S1) x,y,z corrected drift time (µs) WIMP search data 350 cathode grid radius 2 (cm 2 ) kevnr S1 x,y,z corrected (phe) gate grid wall face wall corner 160 events in ER band / 118 kg fiducial Fit data to combined sig & bkg ( 127 Xe, 85 Kr, 214 Pb, Compton)! Profile Likelihood Ratio test consistent with all bkg.

20 !" Spin Independent Cross Section Upper Limit WIMP nucleon cross section (cm 2 ) DAMA/LIBRA Favored CoGeNT Favored CRESST Favored CDMS II Si Favored Edelweiss II XENON0(2012)-225 live days LUX (2014)-85 live days Phys. Rev. Lett. 112, (2014) 1 2 m WIMP (GeV/c 2 3 ) ZEPLIN III CDMS II Ge

21 LUX: improvements to 2013 data reconstruct double scatter Single Scatter (S1, 1xS2s > 0 phe) water-shield! displacer DD n generator Lower S1 threshold new calibrations better photon counting Sensitive down to 3.3 GeV Model detector walls: better fiducialization ~% more exposure still a few weeks away Light yield energy (kev)

22 Rate (counts/(kev tonne day)) New results from XENON-0 Search for leptophilic or Mirror DM electron recoils in data Turn off NR discrimination to test ER interpretation of DAMA signal model dependent electronic structure Iodine vs. Xenon Conservative assumptions For AV coupling ruled out at 4.4σ For Mirror DM ruled out at 3.6σ maximize coupling for cross-check 30 DAMA/LIBRA amplitude 0% Mod. DM Mar May Jul Sep Nov Jan Mar Science 21 August 2015 [ ] DC rate all bkg XENON S1 (PE) Rate (counts/pe/tonne/day) ) 2 (cm Axial-Vector cross-section σ 0 χ e Mean electronic recoil energy (kev) DAMA/LIBRA annually modulated spectrum (2-6)keV interpreted as leptophilic DM, axial-vector coupling mirror DM XENON0 70 summer live days FIG. 1: Fig. 1. Conceptual illustration of the analrealizing such a highly modulated signal [3, servatively consider it as the case that is mos to exclude. The dark matter-induced rate w DAMA/LIBRA (3σ) zero on December 2nd, and twice the measu tion amplitude XENON0 on(90% June C.L.) 2nd. It follows tha optimized time interval to consider for be To find this interval, the signal expected in was simulated for di erent time intervals cen June 2nd. We take into account uncertaintie ing statistics in XENON0 and DAMA/LI as the systematic uncertainty from the conv energy into S1 [16]. The optimum time inte to be 70 live days around June 2nd, roughly SK, χχ -38 ττ (90% C.L.) SK, χχ νν (90% C.L.) WIMP Mass m χ (GeV/c )

23 Liquid Lev Radon Level [ Bq/kg] Cut Acceptance Unbinned&PL&analysis&of&ER& New results from XENON-0 0 Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12 (d) Radon inside LXe (Signal&sample)& Test annual modulation signal for electron recoils with AV coupling 90 Background%% ModulaEon% RMS/Mean Acceptance% 80One year from%known%air%leak% 8.5% span Free global fit to modulation parameters from 7-500d: 1σ days 15 with largest 50 Local fit to 1 year to get phase & amplitude 05 MulOplefscaher& signal Normalized% 1 (e) Average Cut Acceptance 2.8σ for singles Total%% - also in multiples RMS/Mean kev Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/ Exclude DAMA parameters at 4.8σ FIG. 1: Fig. 1. Conceptual illustration of the an ysis. Shown is the DAMA/LIBRA rate (red) [20] w 2. 8 XENON collaboration, thearxiv: modulated rate in (2(accepted 6) kev from in Science) 0.7(&&& 0 ),&A=0,&for&several&samples& the fit paramet 9% 6 in [4] (dark red). The distribution 2 of the XENON0 l 4 get the contribution XENON collaboration, at a given arxiv: recoil energy. (accepted Given in PRL) Mean electronic recoil energy (kev) the time 5 (blue) 6 is indicated 7 8 with its 9 average background rate 5.3events/(keV tonne day), which shows dents due to ma requirement 0.6 that the energy deposited in the detector Mar/11 tenance or calibration campaigns. The region between t DAMA/LIBRA annually modulated (f) May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12 must be more than the binding energy of the electron, High&energy& dashed lines (green) Expected indicates the 70 summer live days wh 2.5 Single-scatter rate spectrum (2-6)keV interpreted as XENON0 the modulated signal DAMA/LIBRA is expected to be largest. the largest contribution to the rate in a sodium iodide (Control&sample)& kev leptophilic DM, axial-vector coupling 2 RMS/Mean 95% C.L. mirror DM target comes from the 3s shell of iodine. The contributions 1.5 from sodium are two orders of magnitude smaller. We interpret data from the XENON0 detector th 51% 99.73% C.L. expected 88 XENON0 70 summer live days best fit phase from were acquired between February 28, 2011 and March 3 The momentum-space 1 wave functions for xenon atoms for a total exposure DM halo of live days and 34 kg fid and iodine anions are nearly identical as a result of their cial mass. We have previously searched this data set spin-independent [14] and spin-dependent [15] WIM similar electron structure. This has the important consequencemar/11 that amay/11 comparison Jul/11 between Sep/11 Nov/11 sodiumjan/12 iodide Mar/12 and 22 arxiv: (Accepted tronicinto recoils PRL) [16]. XENON0 is located in the Gr induced nuclear recoils as well as for axion-induced el 0 xenon is independent of the dark matter halo. The ratio Time Sasso underground laboratory. It consists of a liqu 00 xenon target that is operated as a low-background tim of the August&5,&2015& calculated di erential rates in xenon Patrick&de&Perio&@&DPF2015:&XENON&Enlightening&the&Dark& and sodium projection 120 chamber [17]. 180Each particle interaction 8128& S1 (PE) sults in two signals: Phase The [Days] prompt -2log(L scintillation 1 /L max ) sign Phys. iodide Rev. Lett. are Electronic 115, shown inrecoil Fig. (2015) 2event [ ] as arate function in 34 of kg deposited LXe for energy, considering single-scatters the full versus shell time structure. (many This other ratio detector has FIG. 3: Fig. 3. Contrasting (S1) is used here for energy estimation, and the d Dan Akerib DAMA/LIBRA modulated SLAC / Kipac / Stanford layed ionization spectrum XENON0 signal as (S2) would allows data be for seen 3Dwith TAUP vertex 2015 reco negligibleparameters dependence monitored the WIMP as well) mass. DAMA/LIBRA. in XENON0 The (for DAMA/LIBRA struction. axial-vector DataWIMP-e reduction modulated - scattering) is performed spectrum in order 24 to lect single-scatter low-energy (< kev) recoils in t Rate [Counts/Day] Probing&ModulaOon&Signals&in&XENON0& data&assuming&periodic&signal& hypothesis&(&&& 1 ):& 0.95 & observed%events% 3.9% Compare&to&null&hypothesis& Constraint%terms% -2log(L 1 /L max ) Amplitude Rate [events/(kev tonne day)] (counts/pe/tonne/day) Singlefscaher& Rate (counts/(kev tonne day)) (Control&sample)& 30 DAMA/LIBRA XENON0 (red), interpreted as WIMPs scattering through axial-vector 3

24 FIG. 12: The 90% C.L. upper limit for spin-independ PandaX - 2 Phase LXe TPC PandaX-1 5 KeV NR threshold probing M< GeV 25 kg fid in 125 kg instrumented 7 events ~ expected background (S2/S1) x,y,z corrected log kev nr S1 x,y,z corrected [PE] -40 ) stage 1 - favorable light collection gives low threshold Jing Ping Lab WIMP mass (GeV/c ) 2 WIMP-nucleon cross section (cm PandaX-I 2015 XENON0, 2012 LUX 2013 SuperCDMS 2014 DarkSide50 CRESST-II new CDEX 2014 CoGeNT 2014 CDMS-II Si DAMA 3 sigma PandaX

25 PandaX - 2 Phase LXe TPC PandaX-1I - same vessel / infrastructure 300 kg fid in 500 kg instrumented Commissioning - physics run starts in kg x 1year

26 XENON-0 XENON-1T / nt 3.3 tons LXe / 2.0 tons active Building and commissioning well underway Start of science expected 2015 Expand to 7 tons LXe - replace inner vessel and TPC

27 LZ: LUX + ZEPLIN tons LXe / 7 active / 5.6 fiducial 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 System test HV+RFR+grids HV water shield 7 ton LXe TPC scintillator detector LUX 2014 PRL LUX projection (300d) LZ (00d)

28 single-phase L

29 Single Phase Liquid gon DEAP MiniCLEAN 500 kg instrumented /150 kg fiducial DEAP MiniCLEAN SNOLAB Cube Hall 3600 kg instrumented 00 kg fiducial

30 F prompt kev ee Pulse Shape Discrimination 39 (β) 1Bq/kg DEAP: 9 events in RoI / 3 year Recoil discrimination from prompt fraction: 0:200ns / 0:μs 90% recoil detection efficiency kev γ ( Am) photoelectrons Events/keVee/kg/day Nuclear recoil 3/4 singlet (7ns) kev ee photoelectrons All events After PSD Signal production in liquid nobles Figure 3. Results from the DEAP-1 7-kg liquid argon prototype detector atsnolab.(left) Heat Heat Signal production in liquid nobles e - e - e - S2 + Ion * Excitation Branching ( e - e - e - S2 + Ion * Excitation Branching ( 2 + Ionized molecule 2 + Ionized molecule Recombination 2* Recombination 2* singlet, 7ns triplet, 1.6us singlet, 7ns triplet, 1.6us ) sketched for nuclear recoils Electron recoil 2/3 triplet (1.6μs) ) sketched for electron recoils S1 S1 S1 S1

31 PSD in DEAP-1 gon 7 discrimination stats 6 Analyzed Events: 1.23e kg L Counts 4 3 Prob of 1+ ev from random pileup = kevee ( pe) F prompt : 120 to 240 pe kev r Leakage pe/kevee Light collection expect 8pe/keVee pe/kevee kev ee

32 DEAP construction acrylic vessel (AV) light guides filler blocks, PMTs filler blocks steel shell 8-meter water tank PMTs thermal insulation light guides PMT assembly acrylic vessel SS pressure vessel

33 Recent progress of DEAP-3600 Resurfaced inside of AV in low-rn env. end of 2014 PMT system operational at end of 2014 calibrated with light sources Inner wavelength shifter deposited in AV June 2015: 1 μ TPB Next: steps are commissioning with argon gas followed by cooldown/liquid argon fill by year end

34 DEAP reach & plans 3 year exposure projecting zero background after PSD 8 pe/kevee - 15 kevee threshold <0.2 evts 39 from 1.6x 9 <0.2 wall alpha after fiducialization (from 150 expected) <0.2 n after fiducialization (30) First few months ~ current limit Development of 50-ton fiducial

35 MiniCLEAN Top Hat Demonstrator with 500 kg active / 150 kg fiducial Inner surface of optical modules define active volume Surface backgrounds managed on smaller scale Optical modules installed into metal inner vessel ports No acrylic vessel scalability Cryogenics allows neon - WIMP beam off data PMT Light Guide Acrylic Plug

36 MiniCLEAN Fully assembled - argon gas data Natural run - cool down started Spiked 39 run - to demo0x better PSD towards 150 ton analysis techniques developed on MC ~x improved PSD treat photon arrival times in detail singlet Gas data Standard Fprompt Likelihood ratio: PMT timing log(counts) triplet time arxiv: v1

37 single-phase LXe

38 XMASS XMASS-1 Single-phase LXe detector 642 PMTs / 835 kg total 2013 refurbishment: x reduced bkg x lower than LUX, XENON0 (Fiducial) Simple geometry emphasizes Light collection 14 pe/kevee / 0.3 kev thr. Position reconstruction / self-shielding 40 kg fiducial at 40 kev threshold

39 XMASS DM - new result 0.82 ton - yr 8G 7GeV/c 2 x -40 cm 2! 8GeV/c 2 x -40 cm 2 fixed phase; fit to data Annual modulation for two WIMP cases plotted A 2 Nuclear recoil signal model Full modulation analysis fixed phase Limit consistent with previous xenon results Xe-S2 LUX DAMA/LIBRA (2009 Savage) XMASS2013 CDMS-Si CoGent ML (2014) XENON0 XMASS

40 XMASS program & expected reach XMASS-1I XMASS-1 XMASS kg, 0 kg Fiducial volume (FV) φ80 cm, 642 PMTs 5 ton, 1 ton FV φ1.5 m, ~00 PMTs 25 ton, ton FV φ2.5 m XMASS I - ann mod limit; adding 2nd year of data XMASS 1.5 in 2016 XMASS-II dark matter, pp solar ν, 0ν2β pe

41 two-phase L

42 2-Phase Liquid gon TPCs DarkSide DM

43 2-Phase Liquid gon TPCs PSD triplet vs singlet background rejection + Ion * 2 + Ionized molecule e - e - e - S2 Recombination 2* singlet, 7ns S1 ER Heat Excitation triplet, 1.6us S1 + Ion * 2 + Ionized molecule e - e - e - S2 Recombination 2* singlet, 7ns S1 NR Heat Excitation triplet, 1.6us S1

44 2-Phase Liquid gon TPCs S2 / S1 for ER vs NR background rejection + Ion * 2 + Ionized molecule e - e - e - S2 Recombination 2* singlet, 7ns S1 ER Heat Excitation triplet, 1.6us S1 + Ion * 2 + Ionized molecule e - e - e - S2 Recombination 2* singlet, 7ns S1 NR Heat Excitation triplet, 1.6us S1

45 DarkSide 50 kg fiducial in Gran Sasso with Underground argon outer neutron & muon detectors Single phase run with A Use PSD rejection 300x background reduction from underground argon 00x suppression in 39 S2 position correction to improve energy resolution Also fiducialization, S2/S1 s] kg Events / [80 PE Prompt Fraction (f90) kg-d Atm. ~ s of years Und. atmospheric and underground argon at 200 V/cm A < 1/300 < 1/00 U 39 in U < 1 mbq/kg 85 Kr in U ~ 2 mbq/kg Physics Letter B 743, 456 (2015) NR acceptance band 39 S1 (PE) ~ energy scale A (200 V/cm, LSV anti-coinc.) U (200 V/cm, LSV anti-coinc.) 39 (from global fit) 85 Kr (from global fit) S1 [PE] 8

46 DS-50 limit and Future Plans A 50 day exposure - PSD cuts all bkg U 70 day exposure - results soon expand NR acceptance 2-3 year run - sufficient PSD to rejection ER bkg [cm 2 ] σ Neutrino Limit WARP (2007) CDMS (2009) PandaX-I (2014) DS-50 (2014) XENON-0 (2012) LUX (2013) Dark Side 20k ARGO ARGO 300 ton (200 fid.) DS-20k 30 ton L (20 fiducial) [GeV/c ] 2 1 event from neutrino-induced nuclear recoil 3 M χ 4

47 DM Year-long operation 2 tons L in single-phase - PSD demonstrated on 39 Run 2 - install TPC field cage and SiPM test array PSD / light collection limits by QE of large PMTs SiPM - single photon counting with high QE; dark current at 80K looks manageable for m 2 arrays Prompt fraction NR region 39 arxiv:

48 Design study group for tons! Darwin 160 kg 3.3 tons LXe: tons arxiv: ] 2 WIMP-Nucleon Cross Section [cm SI[cm 2 ] ν-line (Billard) % discrimination, 30% NR acceptance, LY = 8 pe/kev at 122 kev arxiv: CDMS-Si DAMA/Na JCAP01 (2014) 044 num. events: CRESST-II SuperCDMS DAMA/I DarkSide-50 77, , , 60 PandaX XENON WIMP Mass [GeV/c ] 0 t.y floor 200 t.y arxiv: m [GeV/c 2 ] Update: Newstead et al., PRD 88, 2013 LUX DEAP-3600 XENON1T XENONnT / LZ vesc = 544 ± 40 km/s v0 = 220 ± 20 km/s =0.3 ± 0.1 GeV/cm 3 DARWIN (200 t y) DARWIN (500 t y)

49 Light WIMPs and Liquid Helium Kinematically m x 1 x = GeV/c favorable 2 Good NR light yield m x = 0 GeV/c 2 Hertel & McKinsey Event Rate [00 kg kev y ] M x = 1 GeV/c 2 Xe Ge Si Ne He Event Rate [00 kg kev y ] kev Seidel counts (scaled) Na22 data Recoil Energy [kev] PMT anti-coincident: mixture of singlet photons and triplet quenching (13 s lifetime) PMT-coincident: prompt singlet photons only Recoil Energy [kev] roton propagation - thermal signal outgoing atom calorimeter recoil discrimination? 0.2 incoming phonon or roton θ [ev]

50 Liquid nobles summary Saw 4 main approaches across 8 major programs Already major impact on WIMP DM since 2007 Several new results expected through 2016 Primary approach at GeV and above Challenges, yes HV, target acquisition, purity & storage, pp solar Realistic path to neutrino floor over ~ next decade-ish WIMP nucleon cross section cm PICO250-C3F8 SuperCDMS SNOLAB NEUTRINO C OHER ENT SCATTERING 7 Be Neutrinos SuperCDMS Soudan CDMS-lite SuperCDMS Soudan Low Threshold XENON S2 (2013) CDMS-II Ge Low Threshold (2011) 8 B Neutrinos CoGeNT (2012) CDMS Si (2013) CRESST DAMA EDELWEISS (2011) WIMP Mass GeV c 2 SIMPLE (2012) Atmospheric and DSNB Neutrinos COUPP (2012) ZEPLIN-III (2012) CDMS II Ge (2009) SuperCDMS Soudan Xenon0 (2012) DarkSide 50 LUX Xenon1T XENONnT DEAP3600 PICO250-CF3I DarkSide G2 DARWIN NEUTRINO COHERENT SCATTERING LZ WIMP nucleon cross section pb