Liquid Xenon Scintillator for Dark Matter Detection

Transcription

1 Liquid Xenon Scintillator for Dark Matter Detection Recent Results from the XENON10 Experiment Kaixuan Ni (Yale) IEEE - 9th International Conference on Inorganic Scintillators and their Applications Winston-Salem, NC USA June 4-8, 2007

2 What is dark matter? Dark matter represents more than 20% of the Universe, only from its gravitational effect. Dark matter particles should be neutral, stable, heavy and interact very weakly - Weakly Interacting Massive Particle (WIMP). Many theories beyond the Standard Model of particle physics provide WIMP candidates. One of the well motivated theory is supersymmetry: every Standard model particle has a super partner If neutralino is the lightest supersymmetric particle (LSP) and stable, neutralino can be the perfect candidate for a dark matter WIMP. Its cross-section is within the reach of the current direct detection experiments. 2

3 Direct Dark Matter Detection Galactic Halo WIMP χ Elastic Scattering Target V~230 km/s Nucleus Recoil Nucleus ~10 kev χ 3

4 Another Signal over Background Problem R M det M N ρσ < v > <0.05 events/kg/day (10 kevr threshold) Signal Integrated Rates Above Threshold low energy threshold large mass (~ ton scale) background suppression Differential Rates passive shield deep underground gamma background discrimination 4

5 Liquid Xenon Scintillator for Dark Matter Detection High scintillation yield (50,000 photon/ MeV), relative easy detection of the 175 nm light, almost intrinsic transparent low energy threshold Available in large quantity ($1000/kg) and scalability large mass Kr-free Xe available commercially and can be further removed by purification intrinsic background free Ionisation Electron/nuclear recoil wavelength depends on gas e.g. Xe 175nm Ar 128nm Excitation Xe * +Xe Recombination depends on type of recoils (stronger for nuclear recoils) Xe + Xe 2 + +Xe +e - (recombination) Xe ** + Xe discrimination between background (mostly electron recoils) and signal (nuclear recoils) events more than 99.5% background events are removed self-shielding further bkg reduction 175nm Nigel Smith, RAL Triplet 27ns 2Xe Xe 2 * Singlet 3ns 2Xe 175nm time constants depend on gas e.g. Xe 3/27ns Ar 10/1500ns 5

6 Two-phase Xenon Detector with 3-D Sensitivity nuclear recoil WIMP or Neutron Gamma or Electron 6 electron recoil

7 The XENON10 Collaboration Columbia University Elena Aprile (Spokesperson), Karl-Ludwig Giboni, Maria Elena Monzani, Guillaume Plante, Roberto Santorelli and Masaki Yamashita RWTH Aachen University Laura Baudis, Jesse Angle, Alfredo Ferella, Alexander Kish, Aaron Manalaysay and Stephan Schulte Brown University Richard Gaitskell, Simon Fiorucci, Peter Sorensen and Luiz DeViveiros University of Coimbra Jose Matias Lopes, Luis Coelho, Luis Fernandes and Joaquin Santos CWRU Tom Shutt, Peter Brusov, Eric Dahl, John Kwong and Alexander Bolozdynya Livermore National Laboratory Adam Bernstein, Norm Madden and Celeste Winant Rice University Uwe Oberlack, Roman Gomez, Christopher Olsen and Peter Shagin Laboratori Nazionali del Gran Sasso Francesco Arneodo and Serena Fattori Yale University Daniel McKinsey, Louis Kastens, Angel Manzur and Kaixuan Ni 7

8 The XENON10 Detector Pulse tube refrigerator 15 kg LXe 89 PMTs Vacuum Cryostat 8

9 XENON10 at Gran Sasso Underground Laboratory (Italy) below 1400 meter of rock XENON10 Detector Pb/Poly Shield 9

10 XENON10 at the Gran Sasso Underground Laboratory Xe Gas Circulation and Purification System DAQ Shield door closed Slow Control 10

11 XENON10 Live-Time / Dark Matter Run Stability ( ) WIMP search end 92% live High Stats Gamma Calibrations Periodic Gamma Calibs Neutron Calibration High Statistics Gamma Calibs + 1 Neutron Calib NON BLIND WIMP search data ~20 live days (Sept) + 20 live days dispersed (Oct-Feb) BLIND WIMP Search results from 60 live day (Oct-Feb) 11

12 XENON10 Calibration LNGS S1 S2 S1 S2 12

13 XENON10 Gamma/Neutron calibration Electron Recoil Mean Cs-137 S2 threshold (300 pe) S1 threshold (4.4 pe) Nuclear Recoil Mean AmBe ~ 99.5 % gamma events are rejected below nuclear recoil mean

14 Anomalous Leakage Events due to non-active LXe (S2/S1)WIMP < (S2/S1)Gamma Sensitive Volume (15 cm) Reverse Field Region (1.2 cm) S1 No S2 S2 e- e- e- S1 E-field cathode E-field S2/S1 ratio is reduced since S1 has two contributions, but S2 has only one result is a smaller S2/S1 value than a regular single scatter event, leaking into the signal region Incoming Particle S1 no S2! S2 A S1-hit patten cut is defined to remove these anomalous events. Acceptance of good events: 86% 14

15 Self-shielding XENON10 Detector near top PMTs near bottom PMTs Z (15 cm total) Fiducial Volume chosen: 15 < dt < 65 μs, r < 80 mm (5.4 kg fiducial mass out of 15 kg) Overall Background in Fiducial Volume ~0.6 event/(kg day kevee) 15

16 XENON10 WIMP Search Data 136 kg-days Exposure= 58.6 live days x 5.4 kg x 0.86 (ε) x 0.50 (50% NR) ~1800 events kevr WIMP Search Window 16

17 XENON10 WIMP Search Data 136 kg-days Exposure= 58.6 live days x 5.4 kg x 0.86 (ε) x 0.50 (50% NR) ~1800 events kevr noise event WIMP Search Window 16

18 XENON10 WIMP Search Data 136 kg-days Exposure= 58.6 live days x 5.4 kg x 0.86 (ε) x 0.50 (50% NR) ~1800 events Statistical leakage from electron recoil band kevr noise event WIMP Search Window 16

19 XENON10 WIMP Search Data 136 kg-days Exposure= 58.6 live days x 5.4 kg x 0.86 (ε) x 0.50 (50% NR) ~1800 events Statistical leakage from electron recoil band Anomalous events due to non-active Xe kevr noise event WIMP Search Window 16

20 WIMP-Nucleon Cross-Section Upper Limits arxiv: 0706:0039 [astro-ph] CDMS II XENON10 best previous published limit current results (no bkg subtraction) supersymmetry models 17

21 Upgrade XENON10 to XENON10+ Lower background Active LXe Target: 60 kg Total PMTs: 250 To be deployed in 2007 x10 sensitivity Bell Top PMTs Active LXe Target Bottom PMTs Grids Structure Teflon Panels with HV Racetracks Active LXe Shield Shield PMTs Cathode Mesh Vacuum Cryostat 18

22 Towards the discovery of Supersymmetric Dark Matter 7) 200 ( 0 N1 O XEN 08) ( N ENO X ) T( N1 O XEN 19

23 Towards the discovery of Supersymmetric Dark Matter LXe scintillator has demonstrated its capability for direct dark matter detection. And we may soon find out the nature of dark matter. 7) 200 ( 0 N1 O XEN 08) ( N ENO X ) T( N1 O XEN 19