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Dark Matter search with ELEGANT VI CaF 2 detector

Dark Matter search with ELEGANT VI CaF 2 detector. Introduction ELEGANT VI detector Photon counting Analysis Summary & Prospects OGAWA Izumi (Osaka University). CaF 2 scintillation Detector. 19 F : Search for spin coupled Dark Matters large s 48 Ca : Search for 0 nbb decay

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Dark Matter search with ELEGANT VI CaF 2 detector

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  1. Dark Matter search with ELEGANT VICaF2 detector Introduction ELEGANT VI detector Photon counting Analysis Summary & Prospects OGAWA Izumi (Osaka University) TAUP2007

  2. CaF2 scintillation Detector • 19F : Search for spin coupled Dark Matters • large s • 48Ca : Search for 0nbb decay (talk by S. Umehara, on 14th ) • highest Q-value least BG expected Natural abundance 0.187% TAUP2007

  3. 23 CaF2 modules ~3.5 kg 19F ~7.7 g 48Ca Background reduction least material : non hygroscopic 4p active shield CaF2(Eu)+CaF2(pure) roll-off ratio segmentation CsI(Tl) veto detector passive shield OFHC Cu(t:5 cm), Pb(t:10 cm) air-tight box + N2 gas purge Rn in the air LiH + paraffin(t:15 mm), Cd sheet(t:0.6 mm), and H3BO3+H2O tank neutron ELEGANT VI Surrounded by H3BO3 loaded-water tank TAUP2007

  4. PICO-LON TAUP2007

  5. CaF2(Eu) & CaF2(pure) CaF2(pure) as light guide active shield against PMT CaF2(Eu) is not transparent for U.V. light • CaF2(Eu) : from BICRON catalogue • CaF2(pure) : measured value TAUP2007

  6. CaF2(Eu) n = 1.44 CaF2(pure) n = 1.47 Quartz window PMT PMT VL VR Visible light U.V. light Roll-off ratio VL,VR: ADC channel from left & right PMT TAUP2007

  7. Low energy signal by CaF2 scintillator • CaF2(Eu) long falling time (~ 1msec) ~0.5 keV/photoelectron 4 msec gate width baseline fluctuation one photoelectron signal fluctuation noise etc…. ADC TAUP2007

  8. Flash Scaler • Flash scaler • like multichannel scaler (MCS) • dwell time : 50 – 100 nsec • each channel : 8 bits scaler CAMAC module clock F A S T A m p l i f i e r 3 0 0 M H z F l a s h s c a l e r D i s c r i m i n a t o r P M T A D C Signal from PMT Discriminator output Clock signal Flash scaler output 1 2 1 1 3 0 1 1 TAUP2007

  9. Single photon counting in low energy region • Improvement in energy resolution • free from baseline fluctuations single photoelectron • Reject the backgrounds fired at CaF2(pure) crystals Roll-off cut pure Fitting by simple binominal function Eu P : probability counted by left (right) PMT N : total photon number counted Roll-off spectrum by ADC TAUP2007

  10. Roll-off ratio by single photon counting • Fitting by Binominal functions for each Ntot Nl,r : number of photoelectrons counted by left/right PMT : roll-off ratio : modified binominal function (coincidence trigger) PEu: determined by calibration run : fitting parameter TAUP2007

  11. Fitting • Fitting with binominal function for CaF2(#12) • Live time 71.12 days(Run-7) pure Eu TAUP2007

  12. Obtained energy specrum • Single crystal, 71.12 days (Run-7) • Many BG events remains in low energy region • BG reduction using other information • Timing information • ADC TAUP2007

  13. Time difference distribution Calibration run (241Am) Horizontal axis: Tdiff= TL(1st p.e.) - TR(1st p.e.) counts T < 0 T > 0 BG run ex) Ntot=NL+NR=7 In BG run, • peaks at Tdiff= 0, ±500 nsec • continuous events Tdiff TAUP2007

  14. PMT Noise • Measurement was done without scintillators • A peak around Tdiff = 0 nsec • flushing at photocathode ? • continuous events • accidental coincidence • cannot identify peaks around Tdiff= ±500 nsec with same DAQ system Tdiff cut TAUP2007

  15. 1000 ADC (ch) 500 0 25 50 # of p.e. ADC cut • ADC vs. # of p.e. counts Calibration run (241Am) ex) NL6, NR=1 BG run ADC (ch) TAUP2007

  16. 21 22 23 24 25 16 17 18 19 20 11 12 13 14 15 6 7 8 9 10 1 2 3 4 5 Analysis • Run 1001 • 8ch Flash scaler for central CaF2 scintillators • mass : 0.29kg x 8 • live time : 199.3 days • Analysis • Time cut • ADC cut • roll-off cut : select single time bin which corresponds to CaF2(Eu) no binominal fit TAUP2007

  17. Recoil Spectra for each crystal #17 #18 #19 counts/keV/kg/day before cut #12 #13 after cut #7 #8 #9 Energy (keV) TAUP2007

  18. exclusion plots for each crystal #17 #18 #19 WIMP-proton cross section (pbarn) #12 #13 #7 #8 #9 WIMP Mass (GeV) TAUP2007

  19. Preliminarly result this work TAUP2007

  20. Summary & Prospects • ELEGANT VI detector • CaF2 scintillators to search for SD dark matter • Photon counting method by Flash scaler • Analysis without binominal fitting • 460 kg･days of data • exclusion plot for SD dark matter • In progress… • Apply the binominal fit to reduce the CaF2(pure) events expected to be ~1/2 – 1/3 in recoil rate TAUP2007

  21. 終 TAUP2007

  22. TAUP2007

  23. CaF2(pure) Tid2 target paraffin CaF2(Eu) Deuteron beam ~0.75 MeV NaI(Tl) ~3.7 MeV n Heavy metal Neutron detector Recoil response calibration (f-value) • Calibration for our crystal 19F(n, n) elastic scattering 3.2 MV Pelletron (~2 mA at 2 MHz) Result (R. Hazama, et al., NIM A482 (2002) 297) TAUP2007

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