Applications of Micro-TPC to Dark Matter Search 1. WIMP signatures 2. Performance of the Micro-TPC 3. WIMP-wind measurement 4. Future works 5. Conclusions Jun. 13, 2003 Atsushi Takeda for the μ-PIC group

1. WIMP signatures Annual modulation Very hard to see… Movement of the earth Expected spectra rate difference is a few % BGs themselves are likely to have it based on the motion of the earth around the sun

WIMP-wind Strongly peaked in the Cygnus direction WIMP-wind blowing from the direction of the solar motion A directional sensitive detector is needed WIMP-wind distribution

2. Performance of the Micro-TPC Micro Pixel Chamber (μ-PIC) Micro Pixel Chamber (μ-PIC) Micro-TPC Micro-TPC μ-PIC: X, Y TPC: Z (drift time) 3D tracking Schematic structure of the μ-PIC Micro-TPC = μ-PIC + TPC Micro pattern gas detector Fine position resolution (400 μm pitch) 2D imaging

10×10cm 2 Pictures of the Micro-TPC Pictures of the Micro-TPC 10×10cm 2 μ-PIC readout TPC TPC gas package 10×10×8cm 3 Micro-TPC has been developed

3D Tracking performance 3D Tracking performance track length > 5 mm (several points, direction) Proton tracks neutron dE/dx (Brag curves) neutron Ar : C 2 H 6 = 9 : 1 (1 atm)

252 Cf run (n+γ) dE/dx [keV/cm] χ 2 /d.o.f 30 0 neutron Na run (γ) dE/dx [keV/cm]500 χ 2 /d.o.f 30 γ-ray discrimination vs dE/dx plot χ 2 vs dE/dx plot neutron events have large dE/dx straight track neutron ( 14 / 500 events ) >95% γ-rays were discriminated n efficiency ~ 1 n efficiency ~ 1 (511 keV γ)

3. WIMP-wind measurement with Micro-TPC Merit recoil track and direction γ-ray discrimination fine pitch (400μm) ⇔ DRIFT(2mm) Mass production Demerit low mass (gas detector)

Target gas Spin-dependent (SD): CF 4, Xe Spin-independent (SI): Xe Gas pressure, target mass threshold: 40 keV track: 5 mm gas Pressure [Torr] Density [g/m 3 ] dE/dx [keV/cm] CF Xe (μ- PIC threshold : 50keV/cm) OK pressure ~ 10×1m 3 detector is needed

~ 10×1m 3 detector prototype : 30×30×30cm 3 large area μ-PIC : 50×50×50cm 3 ×8 = 1m 3 ×8 = 1m 3 1m 3 ×10 μ-PIC drift plane ×8 electronics 1 m 3 volume ×10 modules 50cm 50cm 50cm modularize

spectrum threshold forward/backward >10 Expected signals for SD interaction for SD interaction gas: CF 4 WIMP-p: 0.1 pb recoil asymmetry forward backward WIMP WIND γ F

cos γ more than 5σ asymmetry CF 4 detection possibility CF 4 detection possibility Backgrounds: fast neutron 2×10 -5 cm -2 s ⇒ 0.1 cpd/kg/keV for CF4 (10cm water shield) ⇒ 1600 BG events / 10m×1yr ⇒ 0.1 cpd/kg/keV for CF4 (10cm water shield) ⇒ 1600 BG events / 10m 3 ×1yr / 10m×1yr WIMPs: 260 events / 10m 3 ×1yr

Estimated detection possibility Estimated detection possibility 5σ2σ SISD Xe 10 m 3, 1 year noshield 5σ Xe 30 m 3, 3 years 35cm water shield CF 4 10 m 3, 1 year noshield CF 4 30 m 3, 3 years 35cm water shield 5σ 2σ

4. Future works Gas study CF 4 properties Background study γ-ray discrimination Study of the diffusion effect influence on the sensitivity influence on the sensitivity Energy Calibration track length v.s. energy

5. Conclusions WIMP-wind measurement idea : NOT NEW idea : NOT NEW μ-PIC has a fine pitch (400 μm) μ-PIC has a fine pitch (400 μm)Micro-TPC sensitive to SD and SI factor 10 forward/backward asymmetry CF 4 5σ detection possibility precise studies to do

diffusion for 50×50×50cm 3 Micro-TPC diffusion for 50×50×50cm 3 Micro-TPC ～ 10 cm/μsec 50 cm t ～ 5μsec drift velocity of e - in pure CF 4 D: diffusion coefficient t: drift time diffusion coefficient: D ～ 1.5×10 -3 cm 2 /μsec ～ 2 mm It’s not so large

Preamplifier - ATLAS amplifier shaper discriminator (ASD) chip (64ch/card) - ATLAS amplifier shaper discriminator (ASD) chip (64ch/card) 7.7 Mcps X-ray intensity[mA] DAQ rate[MHz] cm 40cm Readout electronics Readout electronics Position encoding module - 5 FPGAs 40MHz clock

track direction is important track only track+direction F/B ~ 5 F/B ~ 1.3

Expected rate threshold: 40keV WIMP mass: 50 GeV for F, Ar 100GeV for Xe WIMP mass: 50 GeV for F, Ar 100GeV for Xe WIMP- ｐ cross section : 0.1 pb for SD pb for SI gas pressure [torr] density [g/m 3 ] rate [cpd/kg] Event (10m 3 ×1yr) CF Ar Xe(SD) Xe (SI)

S/N calculation threshold: 40keV WIMP mass: 50 GeV for F, Ar 100GeV for Xe WIMP mass: 50 GeV for F, Ar 100GeV for Xe WIMP- ｐ cross section : 0.1 pb for SD pb for SI gas Event (30m 3 ×3yr) F/B ratio Modulation(σ) n BG ×1/100 CF σ40σ Ar σ3σ Xe(SD)1350.1σ1σ Xe (SI) σ5σ

Expected 95 % C.L. sensitivities Spin-DependentSpin-Independent Xe 30 m 3, 3 years 35cm water shield Xe 10 m 3, 1 year noshield CF 4 10 m 3, 1 year noshield CF 4 30 m 3, 3 years 35cm water shield

spectrum Threshold dependency of F/B gas: CF 4 WIMP-p: 0.1 pb forward/backward increases with the increases with the threshold energy threshold energy