SIGN: A Pressurized Noble Gas Approach to WIMP Detection

Transcription

1 SIGN: A Pressurized Noble Gas Approach to WIMP Detection J.T. White Texas A&M University Dark Side of the Universe U. Minnesota, 6/7/2007

2 Why Gaseous Nobles? Original Motivation: Neon Electron mobility possible S2/S1 discrimination fiducial well defined - TPC Another Advantage: Room Temperature Operation!!! Simpler purification No leveling No Cryo,, etc NEW!! S2/S1 Discrimination observed at WIMP Energy scale!

3 Multiple Target Motivation WIMP 1 σ 2 0 scalar A A E_recoil

4 dr de R A 2 Dependence of Recoil Spectra = σ 0 ρ0 2 v min+ ve v min v F ( E ) 2 R erf erf 4vemxmr v0 v0 e

5 Mass / Halo <v> / # species? Xenon Neon

6 Pressurized noble gas Test Cell 12.7 mm Sense Wire Field Tube Primary Scintillation S1 8 mm PTFE Sapphire Windows 12.7 mm TPB Prop. Scintillation S2 S1 S2

7 4-PMT atm Test Cell Field tube PTFE reflector

8 Sapphire Windows TPB coating

9 2.250E-01 R 0.000E E E-01 Z File prefix: tetrav2.eou Plot type: Contour Quantity: Potential (V) Minimum value: 0.000E+00 Maximum value: 4.198E E E E E E E E E E E E E+03 Current view window Field Tuning Adjust field tube potential to optimize E-field uniformity along sense wire

10 Event Waveform (Ne-Xe (0.5%)) Primary (S1) Secondary (S2)

11 Calibration Xe gas: 20 atm 122 kev Gamma (+ some 136) 92 kev e mm 30 kev x-ray Range 92 kev e- ~ 2 mm Range 30 kev x-ray ~ 1 cm Range 30 kev e- ~ 0.2 mm 8 mm 12.7 mm

12 Calibration 122 kev Gamma 92 kev e- 30 kev x-ray unobserved

13 Calibration 122 kev Gamma unobserved 92 kev e- 30 kev x-ray

14 Calibration 122 kev Gamma unobserved 92 kev e- 30 kev x-ray Leff ~ 4.5% if Ws=76ev/ph Qgain ~ 1.2 p.e./e- (here)

15 Neutron Scattering w/ Mono-Energetic Neutrons En En, m θ Θ π Er, M Er Ermax = (4 m M/(m+M) 2 ) En S Wave dn/der CM frame Edge *** Er

16 4-MeV Proton Accelerator at TAMU Tandem van de Graaff Duoplasmatron Ion source up to ~ 15 ua Monochromatic neutrons up to 2 MeV using 7 (Li(p,n) 7 Be reactions. Achieved >1 ua on target >5E6 n/sr/s

17 Results 20 atm ~ 300 psi

18 Digression: Two-Phase Xenon Discrimination Gammas Neutrons S2/S1 TAMU Test Cell AmBe Source Centroid Separation ~ x 2 Acceptance box Recoil Energy (KeVr)

19 Xe 20 atm Nuclear Recoils S2/S1 gammas neutrons Er_max ~ 27 kev

20 S2 Spectra? Co-57 data

21 Xe 20 atm NR Q & L yields 27 kev Assuming Wi = 21.7 ev/e- 39 kev Assuming Leff=4.5%

22 Xe S2/S1 Discrimination Centroid Separation > X4?

23 20 atm Xe Electron Recoils Nuclear Recoils Er edge 39 kev Er edge 20 kev

24 Results 50 atm ~ 750 psi

25 ArXe(0.5%) 50 atm NR Response ~ pb/n Er threshold 40 kevr, Mx=100 GeV Er_max ~ 104 kev

26 Ar Xe(0.5%) Charge Yield Key! (Penning effect ) 85 kev Average over E ~ kv/cm 120 kev

27 ArXe Xe(0.5%) Light Yield Key! E ~ kv/cm E ~ kv/cm

28 Results 100 atm 1600 psi

29 Event Waveforms (Ne-Xe example) Gamma Event Neutron Event Primary (S1) Secondary (S2) Areas Same i.e. ionization same

30 Nuclear Recoil Discrimination: S2 vs S1 Drift regions AmBe Higher field Lower field S2/S1 field (and density) dependent for nuclear recoils Gammas unaffected (Emin ~ 600 v/cm here)

31 Primary Pulse Shape Discrimination

32 S2/S1 AND Primary Shape Discrimination! Primary Pulse Shape Discrimination Gammas Neutrons

33 NeXe(0.5%) 100 atm NR Response ~ Er >= 40 kev Mx=100 GeV Red = 140 kevr Based on S2 Er_max ~ 140 kev

34 NeXe(0.5%) Q&L Yield E ~ kv/cm E ~ kv/cm

35 Light 6 kev 55 Fe 6 kev gamma in Ne-Xe(0.5%) Charge

36 SIGN conceptual design Cylinder WIMP Gas CsI Photocathode Light gain structure using WLS fibers S2 S1 Primary Ionization Prompt Scintillation Photoelectrons

37 Detector Concept Composite Cylinder

38 Composite Vessels Carbon, Kevlar wound Some rated > psi! Used on mass transit (Methane)) Used for Hydrogen fuel cells On jets, spacecraft DOT certified!

39 Hub Structure one example Field Shaping Electrodes Proportional light gain structure WLS Structure

40 Electron Drift Flow

41 Gas Light Multiplier Concept Cirlex plate electron Fluorescence VUV blue or green WLS Structure 100% e- transmission Fluorescence E/P>1 Lit p.e./vuv pho.

42 20 kg 20 atm Xe Prototype 2 m 0.4 m Shielding PMT SS Tube ~0.25 inch wall WLS Fibers CsI

43 Shielding 4 m water shield ~~4-5 m 10 modules 1 ton

44 Plans Phased Program 20 kg Xe 20 atm SS vessel Water shield Only 300 psi Future 200 atm WIMP Mass =???? Halo velocity dispersion =???? Number of species =????