The XENON 10 dark matter search T Shutt

The XENON 10 dark matter search T. Shutt Case Western Reserve University T. Shutt, SNOLAB, 8/22/6 1

The XENON 10 Collaboration Columbia University Elena Aprile (PI), Karl-Ludwig Giboni, Sharmila Kamat, Maria Elena Monzani, , Guillaume Plante*, and Masaki Yamashita Brown University Richard Gaitskell, Simon Fiorucci, Peter Sorensen*, Luiz De. Viveiros* University of Florida Laura Baudis, Jesse Angle*, Joerg Orboeck, Aaron Manalaysay* Lawrence Livermore National Laboratory Adam Bernstein, Norm Madden and Celeste Winant Case Western Reserve University Tom Shutt, Adam Bradley, Paul Brusov, Eric Dahl*, John Kwong* and Alexander Bolozdynya Rice University Uwe Oberlack , Roman Gomez* and Peter Shagin Yale University Daniel Mc. Kinsey, Richard Hasty, Angel Manzur*, Kaixuan Ni LNGS Francesco Arneodo, Alfredo Ferella* Coimbra University Jose Matias Lopes, Luis Coelho*, Joaquim Santos T. Shutt, SNOLAB, 8/22/6 2

Promise of liquid Xenon. • Good WIMP target. • Readily purified (except 85 Kr) • Self-shielding - high density, high Z. • Can separate spin, no spin isotopes 129 Xe, 130 Xe, 131 Xe, 132 Xe, 134 Xe, 136 Xe • ~ Low-background PMTs available • Rich detection media — Scintillation — Ionization — Recombination discriminates between electron (backgrounds) and nuclear (WIMPs, neutrons) recoils Scalable to large masses T. Shutt, SNOLAB, 8/22/6 3

XENON: Dual Phase, LXe TPC “Calorimeter” • Very good 3 D event location. • Background discrimination based on recombination PMTs 5 µs/cm • Modular design: 1 ton in ten 100 kg modules. • XENON 10 Phase: 15 kg active target in Gran Sasso Lab as of March, 2006. Shield under construction. Physics runs start: June 2006. • XENON 100 Phase: design/construction in FY 07 and FY 08 ($2 M construction). Commission and undeground start physics run with 2008. Time XENON Overview T. Shutt, SNOLAB, 8/22/6 - Es ~1 µs --- ~40 ns LXe Ed WIMP A. Bolozdynya, NIMA 422 p 314 (1999). 4

Scintillation Efficiency of Nuclear Recoils Columbia and Yale Columbia RARAF 2. 4 Me. V neutrons p(t, 3 He)n Borated Polyethylen e Lead LXe L ~ 20 cm Aprile et al. , Phys. Rev. D 72 (2005) 072006 T. Shutt, SNOLAB, 8/22/6 BC 501 A Use pulse shape discrimination and To. F to identify nrecoils 5

Nuclear and electron recoils in LXe Case Columbia+Brown ELASTIC Neutron Recoils INELASTIC 131 Xe 80 ke. V + NR Neutron ELASTIC Recoil INELASTIC 129 Xe 40 ke. V + NR Am. Be n-source Upper e dge -sat uration in S 2 137 Cs source 5 ke. Vee energy threshold = 10 ke. V nuclear recoil T. Shutt, SNOLAB, 8/22/6 6

Charge and light yields Charge yield - nuclear recoils Columbia+Brown; Case Aprile et al. , astro-ph/0601552, submitted to PRL Wph -1 zero field mo re rec om bin atio n T. Shutt, SNOLAB, 8/22/6 less zero recombination W-1 W 0 -1 7

Recombination fluctuations Scintillation-based energy Case Combined energy 40 ke. V (n– inelastic) Neutron Recoils • Recombination independent energy: E = W 0 (ne- +ng) — — Improves energy resolution Restores linearity. • Recombination fluctuations fundamental issue for discrimination. • New energy definition itself cannot improve discrimination T. Shutt, SNOLAB, 8/22/6 8

Discrimination at low energy Nuclear recoil data (Case) Electron recoil data Electron Recoil Band Centroid 99% Rejection (MC) Nuclear Recoil Band Centroid Nuclear Recoil Event: 5 ke. Vr • Charge yield increase for BOTH nuclear recoils and electron recoils at low energy. • E> 20 ke. Vr: recombination fluctuations dominate. • Monte Carlo: — >~99% discrimination at 10 ke. Vr. This is value used in XENON 10/100/1 T proposals T. Shutt, 8/22/6 See: SNOLAB, T. Shutt, et al. , astro-ph/0608137 9

Some comments on Ar and Xe: atomic physics surprises • Xe: — — — Drop in recombination for low energy nuclear recoils Energy independence of nuclear recoil recombination. Drop in recombination for very low energy electron recoils • Ar: — — Huge pulse-shaped discrimination needed because of 39 Ar. Very small apparent “Lindhard” factor. • Xe scintillation discrimination: a cautionary tale LAr LXe (Yale) LAr nr er T. Shutt, SNOLAB, 8/22/6 10

XY Position Reconstruction in 3 kg prototype “S 2” signal 122 ke. V g (57 Co) Reconstructed edge events at 122 ke. V Resolution ≈ 2 mm. • Chisquare estimate from Monte Carlo - generated S 2 map T. Shutt, SNOLAB, 8/22/6 5 mm radial cut reduces gamma events in 80 ke. V nuclear recoils region. Inelastic (131 Xe) 110 ke. V inelastic (19 F) + NR 40 ke. V Inelastic 129 Neutron ( Xe) Elastic Recoil + NR 80 ke. V Inelastic (131 Xe) + NR 40 ke. V Inelastic 129 Neutron ( Xe) Elastic Recoil + NR 11

XENON 10: Cryostat Assembly Pulse tube cryocooler Re-condenser PMTs (top 48) LXe Active Gas Region PMTs (bottom 41) Vacuum Cryostat T. Shutt, SNOLAB, 8/22/6 12

XENON 10: Detector Assembly 89 Hamamatsu R 5900 (1” square) 20 cm diameter, 15 cm drift length 22 kg LXe total; 15 kg LXe active LN Emergency Cooling Loop PMT Base (LLNL) Top PMT Array, Liquid Level Meters, HV- FT Bottom PMT Array, PTFE Vessel Grids- Tiltmeters-Case Liquid Level Meter-Yale T. Shutt, SNOLAB, 8/22/6 13

Summary: XENON 10 Backgrounds Monte Carlo studies of Radioactivity (Background Events) from: • Gamma / Electron Gammas inside Pb Shield • • • PMT (K/U/Th/Co) Vessel: Stainless Steel (Co) Contributions from Other Components Xe Intrinsic Backgrounds (incl. 85 Kr) External Gammas - Pb Shield Rn exclusion Detector Performance/Design • Gamma Discrimination Requirements Use of xyz cuts instead of LXe Outer Veto • Neutron Backgrounds • Internal Sources: PMT (a, n) External: Rock (a, n): Muons in Shield Punch-through neutrons: Generated by muons [Background in rock Modeling U. FLORIDA / BROWN/COLU • NOTE: Active Muon Shield Not Required for XENON 10 @ LNGS Neutron flux from muon interaction in Pb shield << Target Level T. Shutt, SNOLAB, 8/22/6 14

XENON 10 Shield Construction - LNGS Red-Shield Dimension Blue-Ex-LUNA Box Dimension Clearance to Crane Hook (after moving crane upwards) 20 mm Brown Design / LNGS Engineering 40 Tonne Pb / 3. 5 Tonne Poly Crane Hook Low-Activity (210 Pb 30 Bq/kg) inner Pb & Normal Activity (210 Pb 500 Bq/kg) Outer Pb Construction Underway: Contractor 2630 mm. COMASUD – Mid May Expect Completion of Installation 2410 mm LNGS (Ex-LUNA) Box Dimensions are critical constraints for shield expansion of shield to accommodate much larger detector difficult Inner Space for XENON 10 detector 900 x 1075(h) mm Clearance Box 450 mm T. Shutt, SNOLAB, 8/22/6 3500 mm 4400 mm 200 mm Clearance Box 450 mm 15

XENON 10: Punch-Through Neutron Backgrounds • High Energy Neutrons from Muons in Rock — — — Poly in shield is not efficient in moderating High Energy Muon-Induced Neutrons Depth is “standard” way to reduce high energy neutron flux (LNGS effective depth is 3050 mwe) Brown Monte Carlos show that: Goal WIMP 1. 3 evts/10 kg/mth: LNGS depth comfortably achieves goal Goal WIMP 1. 3 evts/100 kg/mth: HE Neutrons evts ~1/6 rate of dark matter. Much reduced comfort margin. (Continue to study mitigation strategies) Mei and Hime, astro-ph/0512125, calculate HE neutron/dm ~1/2– 1/3 for Ge detectors at Gran Sasso Depth DM Goal (Rates for Current XENON 10 Shield Design) Ratio HE Neutron BG / WIMP Signal NR Signal Rate Xe @ 16 ke. Vr High Energy Neutron Relative Flux (from muons) Gran Sasso Homestake 3. 0 kmwe 4. 3 kmwe x 6. 5 x 1/5 Soudan 2. 0 kmwe 1. 3 evts/10 kg/mth σ ~ 2 x 10 -44 cm 2 300 µdru x 1/10 x 1/60 x 1/300 1. 3 evts/100 kg/mth σ ~ 2 x 10 -45 cm 2 30 µdru x 1. 1 x 1/6 x 1/30 1. 3 evts/1000 kg/mth σ ~ 2 x 10 -46 cm 2 3 µdru x 11 x 2 x 1/3 Additional margin could be achieved using anti-coincidence signal from muon veto (none currently in place for XENON 10) around shield (c. f. CDMSII simulations indicate factor 15 reduction may be possible by tagging pions also generated in muon showers that generate HE neutrons). However, it will be T. Shutt, SNOLAB, 8/22/6 important to verify that such a strategy works before relying on it. For 2 x 10 -46 cm 2 also evaluating water/active shielding wrt all types of background 16

Kr removal • 85 Kr — — - beta decay, 687 ke. V endpoint. Goals for 10, 1000 kg detectors: Kr/Xe < 1000, 10 ppt. Commercial Xe (Spectra. Gas, NJ): ~ 5 ppb (XMASS) 10 Kg-charocoal column system at Case Kr feed purge recovery • Chromatographic separation on charcoal column Cycle: > 1000 separation Xe 200 g/cycle, 2 kg/day 25 Kg purifed to < 10 ppt T. Shutt, SNOLAB, 8/22/6 17

XENON 10 expected background • Dominant background: Stainless Steel Cryostat & PMTs — Stainless Steel : 100 m. Bq/kg 60 Co • ~ 4 x higher than originally assumed, but faster assembly — PMTs - 89 x 1 x 1” sq Hamamatsu 8520 • 17. 2/<3. 5/12. 7/<3. 9 m. Bq/kg, U/Th/K/Co • Increased Bg from high number of PMTs / trade off with increased position info. = Bg diagnostic • Expected background: ~ 0. 4 cnts/kg/ke. V/day (before discr. ) Depth (cm) Electron recoil background 5(Brown) 25 ke. Vee • Analytical estimate Single, low-energy Compton scattering — Very forward peaked. — Probability of n scatters while traversing distance L: — Original XENON 10 Goal <0. 14 /ke. Vee/kg/day T. Shutt, SNOLAB, 8/22/6 Radius (cm) Current estimate: 2 -3 x original goal 18

XENON 10: Underground at LNGS T. Shutt, SNOLAB, 8/22/6 19

XENON Box: March 10, 2006 T. Shutt, SNOLAB, 8/22/6 XENON Box: March 7 2006 20

Test Mounting Of Detector (June 22) T. Shutt, SNOLAB, 8/22/6 21

XENON 10 Example Low Energy Event • • Low Energy Compton Scattering Event S 1=15. 4 phe ~ 6 ke. Vee Drift Time ~38 μs = 76 mm (Max depth 150 mm) Bulk gamma calib shows avg S 1 2. 3 phe/ke. Vee 0. 9 phe/ke. Vr Trigger n>=4 in 80 ns window — Able to trigger on S 1 for 10 ke. Vr with >90% eff — Also catching S 2 triggers (with pretrigger look-back) Noise on separate PMT chans <<0. 1 phe equiv T. Shutt, SNOLAB, 8/22/6 22

Status of XENON 10 • 15 kg detector (~8 kg fiducial) now operational in Gran Sasso • First low background operations in shield started 8/12. • Calibrations ongoing — Dark Matter Data Plotter http: //dmtools. brown. edu al go S II CDM Activated Xe soon • 164 + 236 ke. V lines • 80 ke. V beta. — — Neutron External gammas • Background close to expectation • Results soon. T. Shutt, SNOLAB, 8/22/6 SUSY Theory Models SUSY Theor y Model s 23

Scaling LXe Detector: Fiducial BG Reduction /1 • Compare LXe Detectors (factor 2 linear scale up each time) 15 kg (ø 21 cm x 15 cm) -> 118 kg (ø 42 cm x 30 cm) -> 1041 kg (ø 84 cm x 60 cm) — Monte Carlos simply assume external activity scales with area (from PMTs and cryostat) using XENON 10 values from screening Low energy rate in FV before any ER vs NR rejection /ke. Vee/kg/day Gross Mass 15 kg x 2 linear 118 kgx 2 linear 1041 kg x 10 reduction >102 reduction (Brown) T. Shutt, SNOLAB, 8/22/6 dru = cts/ke. Vee/kg/day Fiducial Mass 24

Scaling LXe Detector: Fiducial BG Reduction /2 • Assuming ER are rejected at 99% for 50% acceptance of NR — Diagonal dashed lines show background x exposure giving 1 event leakage — If rej. 99% -> 99. 5% and acc. 50% -> ~100% then all σ are better by 4 x Low energy rate in FV before any ER vs NR rejection /ke. Vee/kg/day Gross Mass 15 kg σ=4 XENON 10 - 400 mdruee 7 live-days x 8 kg fid 10 -43 “ 118 kg” - 40 mdruee σ = 4 10 30 live-days x 20 kg fid cm 2 x 2 linear 118 kgx 2 linear 1041 kg x 10 reduction -44 cm 2 >102 reduction 1 leakage event (rej 99%) 1 week 1 month “ 1041 kg” - 0. 2 mdruee σ = 2 10 -46 cm 2 1200 live-days x 100 kg fid 1 year 4 years Reference: Current CDMS II 90% CL σ = 2 10 -43 cm 2 for 100 Ge. V WIMP(Brown) T. Shutt, SNOLAB, 8/22/6 dru = cts/ke. Vee/kg/day Fiducial Mass 25