Progress in directional Dark Matter detection Observation of
Progress in directional Dark Matter detection: Observation of Head-Tail Effect with Low-energy Neutrons Denis Dujmic for the DMTPC collaboration TAUP 2007, Sendai September 13, 2007 TAUP 2007, Sendai
Outline 1. Detector & DMTPC Collaboration 2. Calibration with alpha tracks 3. Neutron beam results September 13, 2007 TAUP 2007, Sendai 2
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. September 13, 2007 TAUP 2007, Sendai 3
Motivation A. Zero-background analysis hard with ton-size detectors (e. g. coherent scattering from solar neutrinos [Monroe, Fisher, ar. Xiv: 0706. 3019]) September 13, 2007 B. Unambiguous proof by correlating DM signal with astrophysical phenomena TAUP 2007, Sendai 4
Detection Principle 1. Ionization - low-energy ionization profile? e- 50 Torr E F e- total electronic 2. Drift - electron diffusion spread? 0 V +3 k. V 3. Amplification, scintillation - gain? energy resolution? CCD September 13, camera 2007 TAUP 2007, Sendai 5
Detector Prototype CF 4 gas 100 -380 Torr Drift region: 2. 6 cm, E=580 V/cm Amplification region: Anode: 5 mm pitch, 100 m Ground: 2 mm pitch, 50 m September 13, 2007 TAUP 2007, Sendai CCD Camera Kodak KAF 0401 chip 768 x 512 (9 x 9 mm) Cooled (-20 C) Photographic lens (55 mm) 6 Finger Lakes Instrumentation
Scintillation Profile of Track m 1 A 24 280 Torr of CF 4 5. 5 Me. V alpha tracks 380 Torr Bragg peak 340 Torr 280 Torr Data vs. SRIM 280 Torr 300 Torr 320 Torr 340 Torr September 13, 2007 TAUP 2007, Sendai 360 Torr 380 Torr 7
Diffusion Along Wire Critical parameter� since range for nuclear recoils ~ mm Four alpha sources at different heights in drift region ( z) 0. 5 mm 1. 05 mm 200 Torr September 13, 2007 1. 6 mm 2. 05 mm 340 m for z=1 cm 670 m for z=25 cm TAUP 2007, Sendai Maximum size of drift region 8
Gain, Energy Resolution 150 -350 Torr Calibration of gain, energy resolution with 5. 5 Me. V ’s from Am-241 Light intensity for alphas crossing a wire 2 tracks 1 track 0 tracks September 13, 2007 TAUP 2007, Sendai • E/E: ~9 -15% • gain: <25 ADU/ke. V • stability: ~1/2 day (without flowing gas) • 100 -400 Torr 9
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 September 13, 2007 TAUP 2007, 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 September 13, 2007 TAUP 2007, Sendai 11
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Head-Tail Effect! ar. Xiv: 0708. 2370 Wires at 0 deg: f o n o i t c Dire ons r neut Wires at 180 deg: September 13, 2007 TAUP 2007, Sendai 13
Measure of Head-Tail Effect Skewness of light asymmetry along segment: (dimensionless) Direction tag: < 0 > 0 forward backward Recoil direction September 13, 2007 Recoil direction TAUP 2007, Sendai 14
Head-Tail Results Recoil direction: backward (26± 4)% forward (74± 4)% Filled - wires@0 deg Hollow- wires@180 deg September 13, 2007 TAUP 2007, Sendai 15
Head-Tail Results Fraction of recoils in direction of neutrons� : no asymmetry September 13, 2007 TAUP 2007, Sendai 16
Head-Tail Simulation ± 1 spread in data (points), MC (dashed, shaded) backward forward September 13, 2007 TAUP 2007, Sendai 17
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) September 13, 2007 TAUP 2007, Sendai 18
Control Samples • Null test with neutrons perp. to wires • Same # of recoils to left, right left to right (47. 3± 2. 5%) n F • Alpha track perp. to wires • Symmetric signal ( =0) F right to left (52. 7± 2. 5%) Skewness: < >=0. 032+/- 0. 024 September 13, 2007 TAUP 2007, Sendai 19
Cf-252 Run 3 m. Ci Cf-252 source 3. 6 h live time 5 mg CF 4 (200 Torr) preliminary backward forward no asymmetry September 13, 2007 TAUP 2007, Sendai 20
Background Runs • No source • Unshielded, surface run • ~1 day live time • Cs-137 source (8 Ci) • 1/3 day live time 2 events 0 events 5 mg of CF 4 (200 Torr) September 13, 2007 TAUP 2007, Sendai 21
Summary and Plans § First observation of head-tail effect in low-energy nu� clear recoils (>200 ke. V) § Work on improvements: increase gain (x 2), stability of operation, lower pressure (100 ->50 Torr) § ~1 m 3 chamber underground within a year Head-tail performance with full detector Preliminary MC study September 13, 2007 TAUP 2007, Sendai 22
Backup September 13, 2007 TAUP 2007, Sendai 23
Cf-252 Most of neutrons below threshold for alpha production (~4 Me. V) Neutron energy Energy, angular distribution similar to DM recoils September 13, 2007 TAUP 2007, Sendai 24
Cross Sections Predicted neutron scattering cross sections (ENDF-B/VII. 0) total elastic F(n, n+ )N 14. 1 Me. V September 13, 2007 TAUP 2007, Sendai 45% of F between 100 -800 ke. V 7% of a, 17% of N between 100 -800 ke. V Sample dominated by elastic recoils of fluorine 25
F(n, n+ )N neutrons alphas recoils September 13, 2007 TAUP 2007, Sendai 26
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 X projection y Y projection x September 13, 2007 TAUP 2007, Sendai 27
Head-Tail with Full Detector • Simulation of fluorine recoils with 200 Ge. V WIMPs • Assumes improvements: 20 ->60 counts/ke. V 100 ->50 Torr September 13, 2007 TAUP 2007, Sendai 28
Head-Tail Scan 100 ke. V recoil angle Source Recoil angle 14. 1 Me. V neutrons 80 deg Neutrons from Cf 252 ~57 deg (avg) 200 Ge. V WIMP ~43 deg (avg) total electronic Cf source @200 Torr DT source @200 Torr Cf/DD source <100 Torr September 13, 2007 TAUP 2007, Sendai 29
Size of 1 -Ton Detector DMTPC: 16 x 16 m 3 CMS: 15 x 22 m 3 Gran Sasso Cavern (e. g. ) 20 m 1 ton of CF 4 @50 Torr 100 m Super-K: 41. 4 m (Height) x 39. 3 m (Diameter) UNO: 60 × 180 m 3 September 13, 2007 TAUP 2007, Sendai 30
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