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TAUP2007, Sendai September 13, 2007

Progress in directional Dark Matter detection: Observation of Head-Tail Effect with Low-energy Neutrons. TAUP2007, Sendai September 13, 2007. Denis Dujmic for the DMTPC collaboration. Outline. Detector & DMTPC Collaboration Calibration with alpha tracks Neutron beam results.

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TAUP2007, Sendai September 13, 2007

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  1. Progress in directional Dark Matter detection:Observation of Head-Tail Effect with Low-energy Neutrons TAUP2007, Sendai September 13, 2007 Denis Dujmic for the DMTPC collaboration

  2. Outline Detector & DMTPC Collaboration Calibration with alpha tracks Neutron beam results TAUP2007, Sendai

  3. Dark Matter TPC Collaboration Boston U. S. Ahlen, M. Lewandowska, A. Roccaro, H. Tomita Brandeis U. H. Wellensten. N. Skvorodnev MIT B.Cornell* 1), D.Dujmic, W.Fedus*, P.Fisher, A.Kaboth, G.Kohse, R.Lanza, J.Monroe, A.Piso*, T.Sahin*, G.Sciolla, R.Vanderspek, R.Yamamoto, H.Yegoryan* *) undergraduate student 1) Also Harvard U. TAUP2007, Sendai

  4. Motivation A. Zero-background analysis hard with ton-size detectors (e.g. coherent scattering from solar neutrinos [Monroe,Fisher,arXiv:0706.3019]) B. Unambiguous proof by correlating DM signal with astrophysical phenomena TAUP2007, Sendai

  5. total electronic CCD camera Detection Principle 1. Ionization - low-energy ionization profile?  e- 50Torr F E e- 2. Drift - electron diffusion spread? 0V 3. Amplification, scintillation- gain? energy resolution? +3kV TAUP2007, Sendai

  6. Detector Prototype CF4 gas 100-380Torr Drift region: 2.6cm, E=580V/cm Amplification region: Anode: 5mm pitch, 100m Ground: 2mm pitch, 50m CCD Camera Kodak KAF0401 chip 768x512 (9x9mm) Cooled (-20C) Photographic lens (55mm) Finger Lakes Instrumentation TAUP2007, Sendai

  7. 280Torr 300Torr 320Torr 340Torr 360Torr 380Torr Scintillation Profile of  Track 241Am 280Torr of CF4 5.5MeV alpha tracks 380Torr Bragg peak 340Torr Data vs. SRIM 280Torr TAUP2007, Sendai

  8. Diffusion Along Wire Critical parameter since range for nuclear recoils ~ mm Four alpha sources at different heights in drift region (z) 0.5mm 1.05mm 1.6mm 2.05mm Maximum size of drift region 340m for z=1cm 670m for z=25cm 200Torr TAUP2007, Sendai

  9. Gain, Energy Resolution 150-350Torr Calibration of gain, energy resolution with 5.5MeV ’s from Am-241 Light intensity for alphas crossing a wire 2 tracks • E/E: ~9-15% • gain: <25 ADU/keV • stability: ~1/2day • (without flowing gas) • 100-400Torr 1 track 0 tracks TAUP2007, Sendai

  10. Neutrons vs. WIMPs • Neutron elastic scattering mimics dark matter recoils Fluorine recoil angle wrt wires Fluorine recoil energy Fluorine recoil momentum better aligned with WIMP direction TAUP2007, Sendai

  11. Neutrons vs. WIMPs • Neutron elastic scattering mimics dark matter recoils Fluorine recoil angle wrt wires Fluorine recoil energy Fluorine recoil momentum better aligned with WIMP direction TAUP2007, Sendai

  12. Neutron Beam Setup Anode wires neutrons D + T  He+n(14.1MeV) TAUP2007, Sendai

  13. arXiv:0708.2370 Head-Tail Effect! Wires at 0 deg: Direction of neutrons Wires at 180 deg: TAUP2007, Sendai

  14. Measure of Head-Tail Effect Skewness of light asymmetry along segment: (dimensionless) Direction tag: < 0 forward > 0 backward Recoil direction Recoil direction TAUP2007, Sendai

  15. Head-Tail Results Recoil direction: backward (26±4)% forward (74±4)% Filled - wires@0 deg Hollow- wires@180 deg TAUP2007, Sendai

  16. no asymmetry Head-Tail Results Fraction of recoils in direction of neutrons: TAUP2007, Sendai

  17. Head-Tail Simulation ±1 spread in data (points), MC (dashed,shaded) backward forward TAUP2007, Sendai

  18. Energy vs. Range Correlation between energy (ADC counts) and range (CCD bins): Filled - wires@0 deg Hollow- wires@180 deg (Slope proportional to stopping power) TAUP2007, Sendai

  19. n  F F Control Samples • Null test with neutrons perp. to wires • Same # of recoils to left, right • Alpha track perp. to wires • Symmetric signal (=0) left to right (47.3±2.5%) right to left (52.7±2.5%) Skewness: <>=0.032+/- 0.024 TAUP2007, Sendai

  20. Cf-252 Run preliminary 3mCi Cf-252 source 3.6h live time 5mg CF4 (200Torr) backward forward no asymmetry TAUP2007, Sendai

  21. Background Runs • Cs-137 source (8Ci) • 1/3 day live time • No source • Unshielded, surface run • ~1 day live time 2 events 0 events 5mg of CF4 (200Torr) TAUP2007, Sendai

  22. Summary and Plans • First observation of head-tail effect in low-energy nuclear recoils (>200keV) • Work on improvements: increase gain (x2), stability of operation, lower pressure (100->50Torr) • ~1m3 chamber underground within a year Head-tail performance with full detector Preliminary MC study TAUP2007, Sendai

  23. Backup TAUP2007, Sendai

  24. Cf-252 Neutron energy Most of neutrons below threshold for alpha production (~4MeV) Energy, angular distribution similar to DM recoils TAUP2007, Sendai

  25. Cross Sections Predicted neutron scattering cross sections (ENDF-B/VII.0) total elastic 45% of F between 100-800keV F(n,n+)N 7% of a, 17% of N between 100-800keV Sample dominated by elastic recoils of fluorine 14.1MeV TAUP2007, Sendai

  26. F(n,n+)N neutrons alphas recoils TAUP2007, Sendai

  27. Segment Analysis • Range: count # of pixels above threshold • Measured along anode wires (+/- 3 pixels around wire) • Background estimate from pixels in between wires • Energy: integral of light yield on the wire • Measured in the y direction, perpendicular to anode wires • In +/- 5 pixels around segment, Gaussian fit above flat background Y projection X projection y x TAUP2007, Sendai

  28. Head-Tail with Full Detector • Simulation of fluorine recoils with 200GeV WIMPs • Assumes improvements: • 20->60 counts/keV • 100->50Torr TAUP2007, Sendai

  29. total electronic DT source @200Torr Cf source @200Torr Cf/DD source <100Torr Head-Tail Scan TAUP2007, Sendai

  30. DMTPC: 16 x 16 x 16 m3 CMS: 15 x 15 x 22 m3 Gran Sasso Cavern (e.g.) 1 ton of CF4 @50Torr 20 m 100 m Size of 1-Ton Detector Super-K: 41.4m (Height) x 39.3m (Diameter) UNO:60 ×60 ×180 m3 TAUP2007, Sendai

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