The LUX Dark Matter Search

Transcription

1 The LUX Dark Matter Search The Large Underground Xenon (LUX) dark matter search experiment is currently being deployed at the Sanford Laboratory at Homestake in South Dakota. We will highlight the main elements of design which make the experiment a very strong contender in the field of direct detection, as well as an easily scalable concept. We will also present the potential reach for supersymmetric dark matter detection of the LUX and further LZ programs, within various timeframes ranging from 1 to 12 years. S. Fiorucci - Brown University 1

2 Summary The LUX Experiment Collaboration Particularities of LUX Design Backgrounds and Sensitivity Operations Summary LUX CWRU LUX Sanford Surface Facility LUX Sanford -4850L Davis Lab Outlook and LUX-ZEPLIN Program LZ-S LZ-D SUSY Dark Matter Sensitivity Reach S. Fiorucci - Brown University 2

3 The LUX Collaboration Brown Richard Gaitskell Simon Fiorucci Monica Pangilinan Luiz de Viveiros Jeremy Chapman Carlos Hernandez Faham David Malling James Verbus PI, Professor Postdoc Postdoc XENON10, CDMS Thomas Shutt Dan Akerib Mike Dragowsky Carmen Carmona Ken Clark Karen Gibson Adam Bradley Patrick Phelps Chang Lee Case Western SNO, Borexino, XENON10, CDMS PI, Professor Professor Research Associate Professor Postdoc Postdoc Postdoc Formed in 2007, fully funded DOE/NSF in 2008 Harvard Masahiro Morii Professor Michal Wlasenko Postdoc Lawrence Berkeley + UC Berkeley Bob Jacobsen Professor Stu Loken Professor Jim Siegrist Professor Joseph Rasson Engineer Mia ihm Grad Student Lawrence Livermore BABAR, ATLAS SNO, KamLAND XENON10 Adam Bernstein PI, Leader of Adv. Detectors Group Dennis Carr Senior Engineer Kareem Kazkaz Staff Physicist Peter Sorensen Postdoc University of Maryland Carter Hall Professor Douglas Leonard Postdoc EXO SD School of Mines Xinhua Bai Professor Mark Hanardt Undergraduate Student Texas A&M James White Professor Robert Webb Professor Rachel Mannino Tyana Stiegler Clement Sofka UC Davis Mani Tripathi Professor Robert Svoboda Professor Richard Lander Professor Britt Hollbrook Senior Engineer John Thomson Engineer Matthew Szydagis Postdoc Jeremy Mock Melinda Sweany Nick Walsh Michael Woods IceCube ZEPLIN II Double Chooz, CMS University of Rochester Frank Wolfs Professor Udo Shroeder Professor Wojtek Skutski Senior Scientist Jan Toke Senior Scientist Eryk Druszkiewicz U. South Dakota DongMing Mei Professor Wengchang Xiang Postdoc Chao Zhang Postdoc Jason Spaans Xiaoyi Yang Yale Daniel McKinsey Professor James Nikkel Research Scientist Sidney Cahn Research Scientist Alexey Lyashenko Postdoc Ethan Bernard Postdoc Louis Kastens Nicole Larsen ZEPLIN II Majorana, CLEAN-DEAP XENON10, CLEAN-DEAP

4 LUX Experiment Overview Ultra-low background, 350 kg liquid xenon time-projection chamber Direct detection of WIMP interactions with atomic nuclei To be deployed at the Sanford Underground Lab (SUSEL) mid-2011 Capable of surpassing current sensitivity limits in 2 days of operation Reach: σ χ-p = cm 2 for m χ = 100 GeV/c 2 in 300 days...the rest of the talk is just technical details S. Fiorucci - Brown University 4

5 WIMP Interaction in Xenon S. Fiorucci - Brown University 5

6 LUX Design Double Phase LXe TPC Can measure single electrons and photons Charge yield reduced for nuclear recoils Good 3D imaging Reject multiple scatters Eliminate edge events to take advantage of Xe self shielding Animation by LLNL S. Fiorucci - Brown University 6

7 LUX Design Detector Overview Thermosyphon LN bath column Feed-throughs for cables / pipes Titanium Vessels Radiation shield Anode grid PMT holding copper plates 59 cm 49 cm Dodecagonal field cage + PTFE reflector panels Cathode grid Counterweight S. Fiorucci - Brown University 7

8 LUX Design Water Tank Water Tank: d = 8 m, h = 6 m 300 tonnes, 3.5 m thickness on the sides Inverted steel pyramid (20 tonnes) under tank to increase shielding top/bottom Cherenkov muon veto Ultra-low background facility Gamma event rate reduction: ~10-9 High-E neutrons (>10 MeV): ~10-3 µ neutrons Rock neutrons Rock γ Inverted steel pyramid Rendering by J. Thomson Shield Thickness (m) S. Fiorucci - Brown University Slide design from L de Viveiros 8

9 LUX Design Cryostat Inner vessel: 100 kg Rated 60 psig / vacuum Outer vessel: 130 kg Rated 45 psig / 30 psi Total det mass: ~2.4 t kg of LXe Ultra-low radioactivity inner and outer Titanium cryostats (high strength, low mass) Activity <0.4 mbq/kg in U+Th Cryostats separated by vacuum + superinsulation film Inner cryostat covered with Cu radiation shield Cosmogenic activation of Ti at Homestake altitude gives 46 Sc (89 d) Equilibrium level ~15% of LUX ER background budget, ~5% after 130 days underground S. Fiorucci - Brown University 9

10 LUX Design Internals HV Grids in place and tested Dodecagonal field cage + PTFE reflector panels 122 2" PMT R nm, QE > ~30% U/Th ~10/2 mbq/pmt All tested in LUX 0.1 program Assembly taking place at Sanford Surface Lab since Spring 2010 Copper PMT holding plate S. Fiorucci - Brown University 10

11 LUX Design Thermosyphon Closed loop of LN 2 condensation/evaporation Cold LN 2 bath on top Safe deported cooling No danger from power failure 1 main thermosyphon for rapid cooling Provides 1 kw cooling power Allows circulation at ton/day scale 2 secondary thermosyphons Mounted on cold Cu head ~0.2 kw cooling power Ensure stable operation Technology readily scalable to multi-ton detectors S. Fiorucci - Brown University 11

12 LUX Acquisition System Struck ADC boards run on "Pulse Only Digitization" mode (POD) Average event size (122 PMTs, 700 µs): 60 kb Comparison Xe10 equivalent: ~17 MB Max event rates (100% livetime): Calibration «multi-event» mode: 1.2 khz Background «single event» mode: 300 Hz Trigger through custom DDC-8 logic boards Dedicated 8 channel 14 bit ADCs, sync with DAQ S1/S2 pulse recognition capability Can trigger on either or any combination of both S. Fiorucci - Brown University 12

13 LUX Backgrounds and Signals Goal: < 1 NR event / 100kg / 300 days (50% accept.) Expected ER background ~260 µdru PMT contribution dominant / external sources (10-4 ) 85 Kr < 2 ppt (~10% of LUX ER background budget) 350 kg = full advantage of Xe self-shielding XENON10 WIMP data (5.4 kg fiducial, 59 days) Expected NR background < 500 ndru r Neutrons mostly from (alpha,n) on PMTs Subdominant to gammas after ~99.5% ER discrimination Strength of LUX is in the extremely low ER and single NR background in the fiducial volume 2 days < 1 ER event Equivalent to best current sensitivities 60 days <<1 NR, ~16 ER before discrim. 99.5% Equivalent to 150 days XENON100, zero background 300 days 0.06 NR, 80 ER before discrim. 99.5% Simulated LUX data (100 kg fiducial, 100 days) m X = 100 GeV/c 2 σ = cm2 S. Fiorucci - Brown University 13

14 LUX SI Coupling WIMP Sensitivity (400 days x 1.5 kg) All limits with goal: zero background LUX ~2 days (560 days x 7.5 kg) LUX ~60 days LUX ~300 days S. Fiorucci - Brown University 14

15 LUX 0.1 at Case-Western S. Fiorucci - Brown University 15

16 LUX 0.1 Program Thermosyphon Surface run at Case-Western during kg Xe total mass (260 kg Al displacer) 4 PMT operation, 5 cm drift active region Slow-Control LUX 0.1 at Case Western Gas System Objectives Develop full-scale cryogenics + fluid system In particular high-flow purification/circulation System integration Xe handling, Slow Control, Safety, DAQ, Electronics, PMT mounts, Resistor-chain Bases, Analysis Software Team integration Achievements Detector designed and built Cooldown and stable operation at LXe temperature All PMTs tested and characterized S1 and S2 light observed 200 kg/d circulation, 96% efficient heat transfer Gamma and neutron data with full DAQ + Trigger system Electron drift length > 2m (purification rate ~9h e-folding) S. Fiorucci - Brown University 16

17 LUX 0.1 Heat Exchanger Efficiency > 96% S. Fiorucci - Brown University 17

18 LUX 0.1 Xenon Purity Circulation: 0.2 tonnes / day ~ 9h time constant for purification at 20 slpm (LUX will run at 50 slpm) > 2 m electron drift length achieved ( > 1000 us) with 60 kg target Errors dominated by use of 5 cm test cell drift within large cryostat S. Fiorucci - Brown University 18

19 LUX 0.1 Event Pulses S. Fiorucci - Brown University 19

20 LUX 0.1 Neutron Calibration Results S. Fiorucci - Brown University 20

21 LUX 1.0 at Sanford Lab S. Fiorucci - Brown University 21

22 Sanford Homestake Surface Facility Funded with 70 M$ private donation + 39 M$ from state of SD Davis Cavern 4300 m.w.e 4 µ/m 2 /d Demonstrator for DUSEL, but already competitive! S. Fiorucci - Brown University 22

23 Sanford Lab Surface Facility Full-scale test of LUX deployment Liq/gas system PMT testing DAQ testing S1 trigger efficiency Xe purity Exact duplicate of the underground layout for all major systems 1 m thick water shield designed to allow limited real data taking, even at the surface Expected Gamma rate ~70 Hz, Neutron rate ~30 Hz, Muon rate ~50 Hz Natural detector limit: 175 Hz (PMT gain stability, < 10% event overlap) Will require: S2 gating, reduced PMT gain LUX detector integration on site since November 2009 Detector will be ready for cryogenic operation inside water tank in October 2010 Test and refining of systems will continue through the first half of 2011 S. Fiorucci - Brown University 23

24 Sanford Lab Surface Facility S. Fiorucci - Brown University 24

25 Sanford Lab State of the Davis Cavern Davis Cavern and perchloroethylene Tank 1967 Davis Cavern and perchloroethylene Tank August 04, 2009 S. Fiorucci - Brown University 25

26 Sanford Lab Davis Laboratory (4850L) Construction/excavation design: 95% complete Nov 2009 New 90 m access/safety tunnel excavated Shared access with Majorana facility, also excavated Right now: shotcreting. Soon after: outfitting Two-story, dedicated LUX 17 x 9 x 9.5 m facility, CL 100k Includes CL 1k clean room, control room, counting facility Beneficial occupancy: July-Oct New excavation Lab Rendering by J. Thomson Mine shaft S. Fiorucci - Brown University 26

27 Sanford Lab Davis Laboratory (4850L) The Davis Homestake Left: N-S vertical cross-section Top right: Plan view, level 1 Bottom right: Plan view, Level 0 Level 1 18 m N Access Tunnel 10.5 m Level 0 Access Tunnel Control Room Clean Room Rendering by J. Thomson SRV Xe bladder footprint 12 m 6 m Water Tank Counting Facility 8 m S. Fiorucci - Brown University 27

28 Sanford Lab Davis Schedule Aug : Equipment commissioning complete Aug : Began excavation of new drift Sep : Steel structures removal complete Nov : Detailed Construction Docs 95% complete Jul 2010: Excavation complete now Sep 2010: Rock support & wall finish complete Oct 2010: Begin Lab outfitting Davis Cavern Aug 20, 2009 Jul-Oct 2011: Lab ready Davis Cavern May 22, 2009 Level 4850 Aug 25, 2009 Davis Cavern Aug 24, 2009 S. Fiorucci - Brown University Davis Cavern Sep 01,

29 LZ Program S. Fiorucci - Brown University 29

30 LUX-ZEPLIN (LZ) Program New collaborators from Zeplin III and US institutions Imperial College, London STFC Rutherford Appleton Lab STFC Daresbury Laboratory ITEP, Moscow Moscow Engineering Physics Institute LIP, Coimbra UC Santa Barbara LBNL UK and PT groups to join LUX late 2010, subject to local agencies approval Two phases: LZ-S (3 t), LZ-D (20 t) from DUSEL Program at Homestake L4850 LZ20 baseline design 2 m S. Fiorucci - Brown University 30 LUX

31 LZ Program LZ-S: 3 tonnes detector in Davis water shield (SUSEL) Proposal start: Sept 2009 Bigger 3" PMTs already in testing. Goal ~1 mbq/pmt LZ-D: 20 tonnes detector, part of ISE for DUSEL «ultimate» direct detection experiment Requirements Mechanics, safety: LUX 350kg will demonstrate Light collection: current understanding 20t scale ok Xe purity: LZ-D requires <10-14 Kr/Xe, < ~mbq Rn state of art already demonstrated (SNO, Borexino) + Xe much easier to purify work in progress to achieve high reliability Backgrounds Goal: < 2 neutron events / 3,000 tonne.days (before acceptance cut) PMT background already improved by x2 compared to 2" tubes improvement by x10 likely in near future (currently XMASS has < 1 mbq/pmt) Extensive study of cosmogenic backgrounds in progress still subdominant at ft for 20 tonne scale LED Calibration gain = σ/µ = 35% S. Fiorucci - Brown University 31

32 LZ Program LZ20, ultimate search? Electron Recoil signal limited by p-p solar neutrinos Subdominant with current background rejection Nuclear Recoil background: coherent neutrino scattering 8 B solar neutrinos Atmospheric neutrinos Diffuse cosmic supernova background LZ20 also sensitive to ββ0ν decay in natural xenon up to lifetimes of ~ years! LZ20 reaches this fundamental limit for direct WIMP searches cts/kev r /tonne/1000 days GeV WIMP 10 0 B solar (1e 47 cm 2 L. Strigari E res. conv. ) B solar atmospheric PMT (,n) 1/1 mbq U/Th Nuclear Recoils 100 GeV WIMP (1e 48 cm 2 ) astro-ph/ Electron Recoils 10 4 DSNB 10 1 Nuclear Recoil Energy (kev r ) S. Fiorucci - Brown University Slide design from T. Shutt 32

33 LZ Program - WIMP Sensitivity Projections based on Known background levels Previously obtained e - attenuation lengths and discrimination factors Fiducial volumes selected to match < 1 NR event in full exposure S. Fiorucci - Brown University 33

34 Thank You S. Fiorucci - Brown University 34