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(direct) Dark Matter Searches and XMASS experiment

S. Moriyama Kamioka Observatory Institute for Cosmic Ray Research March 3 rd 2007, KEKTC7. (direct) Dark Matter Searches and XMASS experiment. DM search: status, prospects and difficulties for large scale experiments XMASS experiment. WMAP Cosmic Microwave Background

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(direct) Dark Matter Searches and XMASS experiment

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  1. S. Moriyama Kamioka Observatory Institute for Cosmic Ray Research March 3rd 2007, KEKTC7 (direct) Dark Matter Searches andXMASS experiment DM search: status, prospects and difficulties for large scale experiments XMASS experiment

  2. WMAP Cosmic Microwave Background power spectrum decomposed matter, cold dark matter, and dark energy NASA The Bullet cluster: NASA Red: ordinary matter from X-ray Blue: mass from gravitational lensing Dark Matter in the Universe • A lot of evidences on the existence of DM • Orbital velocities of galaxies in clusters • Rotational speed of galaxies • Gravitational lensing of background objects by galaxy clusters • Temperature distributions of hot gas in galaxies and clusters of galaxies • CMB power spectrum analysis in WMAP • The Bullet cluster • Large scale map for dark matter • … • A lot of evidences on the existence of DM All of them are astrophysical observations. “Direct detection” is an urgent issue now.

  3. WIMP Dark Matter • Particles thermally generated at high temperature decouple when the expansion rate ~ the interaction rate. • Weakly interacting, heavy, neutral, and stable particles can be CDM. • (WIMPs != SUSY here) Increasing <sAv> Comoving number density Nequillibrium X=m/Temperature (time ) E.W. Kolb and M.S. Turner, The Early Universe

  4. Dark Matter in the Milky Way R.P.Olling and M.R.Merrifield MNRAS 311, 369- (2000) • Also, the Milky Way (our galaxy) has a large amount of Dark Matter. Dark Halo Steller disk Buldge

  5. Motion of WIMPs around us WIMPs are randomly moving with Maxwell distribution <v>~270km/sec Earth The solar system is moving at ~230km/sec. The earth is moving at ~30km/sec. The earth is rotating. Sun Annual, sidereal modulation “Wind” of Dark Matter DM density ~0.3GeV/cc 100GeV WIMPs  1 WIMP / 7cm cubic, F=105/cm2/sec

  6. (direct) Detection method • Since they are neutral and stable, what we can expect is only a collision with ordinary matter. • Electron recoil does not give enough energy but nuclear recoil gives ~100keV if mDM~O(100GeV). Energy deposit Dark Matter particles

  7. What is the best target?Recoil spectrum (spin independent) WIMP mass 100GeV • Ge and Xe, and Ar give similar rates. • Annual modulation should be seen. Target Xe Ge June Xe Xe Si Diff. ~6% Ge Dec. Si Red: differential, Blue: integrated Assuming quenching factor of 0.2 R.J.Gaitskell, Ann. Rev. Part. Sci., 54 (2004) 315.

  8. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ u d c s t b nt e ne m nm t H+ H10 H20 H- g g Z0 W ~ ~ ~ ~ ~ ~ ~ ~ u d c s t b e ne m nm t nt Neutralino Candidate: Neutrarino in the Supersymmetric Model • SUSY solves the hierarchy problem, stability of boson mass, and it can predict the gauge coupling unification. The prime paradigm beyond the standard model. • Even if SUSY particles are discovered in LHC, direct detection of DM should be done INDEPENDENTLY. H+ H10 H20 H- A0 g g Z W

  9. Expected cross section to nucleon Y.G.Kim et al. 2002 sSI for proton (pb) • Large space of sSI for proton. • SNOWMASS benchmark, many of them: 10-8-10-10pb General MSSM 10-6 10-8 10-10 (1pb = 10-36cm2 ) 10-12 100 400 700 Mc(GeV)

  10. Mission in the real world • Once we make detector, we have 10~100Hz background by ambient gamma rays and internal radioactive contaminations, and neutrons. • What we need to realize is “1count/100day detector”.  108-9 reduction needed

  11. DM Searches: past DAMA: NaI(Tl) scintillator NaI(Tl) at Gran Sasso Exposure 107 ton day Annual modulation over 7 years 6.3sigma C.L. annual modulation 2-6keV data: 0.02000+/-0.0032 cpd/kg/keV T0=140+/-22 days (exp. 152.5th day) T=1.00+/-0.01 year No modulation: 7x10-4 (c2/d.o.f.=71/37) astro-ph/0307403 LIBRA experiment will reject/confirm the result.

  12. Ionaization EQ Bolometric EP 1st run Oct.03-Jan.04 2nd run Feb.04-Aug.04 BG band ~EQ/EP Signal band Recoil energy (keV) Recoil energy (keV) DM searches: recent, CDMS (Ge) BG from g, e: EQ~EP Signal : EQ~0.3EP Rise time of Ep, timing diff. btw EP & EQ • Blind analysis done. • World best limit obtained: ~O(kg) 4x250g Ge 2x100g Si

  13. CDMS to SuperCDMS:25kg seems to be straight forward

  14. M. Yamashita IDM2006 DM searches: XENON (2 phase LXe) Liquid xenon scintillator with charge coll. Rare gas liquid: scale up, purification easy XENON10: 10kg target first results soon! XENON100: 100kg target 2007-2009 construction

  15. n e 1ms Integrated waveforms WARP Log(S2/S1) n-like e-like CDMSII Pulse shepe parameter  e-like n-like  DM searches: WARP/ArDM (Liquid Ar) S2/S1 + difference of scintillation waveform for e and nuclear recoil P.Benetti astro-ph/0701286 Need to remove 39Ar (0.8Bq/kg) 100 liter detector soon?

  16. 2003 DAMA 10-6pb • 2007 CDMS 10-7pb DAMA • +5-10year 10-9 ~ -10pb CDMSII (current) B. Sadoulet KEKTC6 Sorry for approximate line ~4events/100kg/year Xe recoil E >25keV • 10-12 pb is really challenging!! ~4events/100ton/year Future: larger scale Exp. Y.G.Kim et al. 2002 sSI for proton (pb) General MSSM 10-6 10-8 10-10 10-12 100 400 700 Mc(GeV)

  17. BG required For 10-12pb 10-12pb detection requires Super-K @ keV DAMA NaI ZEPLIN before PSD cut Kamioka Ge CDMSII Heidelberg Moscow Events/kg/keV/day KamLAND (>0.8MeV) DM signal for LXe 100GeV 10-6pb QF=0.2 Super-K Atm, solar neutrino NC nuclear recoil appear

  18. neutron Difficulties appear ~10-9-10-10pb • Scale-up is always accompanied with new background sources which are caused by: • Low E threshold • Surface effect • Impurities in the targets • Insufficient rej. eff. • Neutron background • Small signals • Surface a & b rays • 39Ar, 85Kr • Large # of BG >108 • muon, parts inside Neutron background Target (Ge, LAr, LXe) Neutron BG will be dominated <10-9pb ~Full target scheme i.e. Ge, XENON, WARP single neutron events cannot be discriminated ?

  19. Currently, “gamma rejection” is extensively studied. CDMS, XENON, and WARP have good discriminations with multiple information. • However, <10-9pb, neutron will be most serious BG. It cannot be discriminated. N. Spooner, DM2004 Strategy for larger target, high sensitivity e, g neutron • Neutron shielding by large amount of target itself.  XMASS!

  20. External g ray from U/Th-chain 250cm dia. 23 ton All volume 20cm wall cut 30cm wall cut (10ton FV) Large self-shield effect BG normalized by mass 0 1MeV 2MeV 3MeV g BG can be efficiently reduced in < 500keV low energy region XMASS (liquid Xe sci.) at Kamioka Self shielding with large target for gamma rays MC: g outside Xenon U-chain gamma rays 80cm dia. 800 kg g Blue : γ tracking Pink : whole liquid xenon Deep pink : fiducial volume

  21. Self shield for fast neutrons (5MeV) 250cm dia. 23 ton Single recoil Vertex distribution Evis>5keV n • Assumption: irreducible BG is only single neutron scattering • 1/100 reduction is possible in 30cm thickness. FV # of events (cm-3) Fiducial volume 0 60 120 Red: single recoil Distance from the center (cm)

  22. “Full” photosensitive, large volume detector 23 ton detector, FV 10t 100kg Prototype FV 3kg 800kg detector FV 100kg ～30cm ～2.5m ～80cm Neutron shield 30cm outer layer >1/100 Neutron BG not serious R&D Dark matter search Realize ~FULL COVERAGE Multipurpose detector (solar neutrino, bb …)

  23. 54 2-inch low BG PMTs Hamamatsu R8778 Liq. Xe (31cm)3 Confirmation with a prototype detector done. MgF2 window 16% photo- coverage Vertex reconstruction Large photoelectron Yield can be obtained ~5 p.e./keV Accurate vertex Reconstruction based on light pattern possible

  24. + + + B A C Demonstration with a prototype detector I Gamma ray injection from collimators DATA MC Reconstruction works well Data well reproduced by MC 30cm cube

  25. Demonstration with a prototype detector II 60Co: 1.17&1.33MeV DATA MC 137Cs: 662keV DATA MC 10-1 10-1 Arbitrary Unit 10-2 10-2 ~1/10 10-3 10-3 ~1/200 PMT saturation 10-4 10-4 10-5 10-5 -15 Reconstructed Z +15cm -15 Reconstructed Z +15cm Confirmed Self shielding >2 orders of magnitude agreements Gamma rays Z= -15 Z= +15

  26. Detail design of the 800kg detector GEANT4 base simulation done 6cm RMS for 5keV @ boundary of FV  Good performance

  27. Background of the 800kg detector • Background origins Neutrons: enough by water shield PMT g rays: low BG PMT Radioactive impurities: distillation PMT g n RI in LXe

  28. Background from PMTs (238U g) Normalized by volume (day-1kg-1keV-1) Fiducial cut Red: 100kg 1.8 mBq-238U/PMT, most clean PMT ever made (achieved) c.f. usual “low” activity PMT ~O(1Bq/PMT) BG <100keV 5cm self shield: ~10-3 /day/kg/keV 10cm self shield: ~10-4 /day/kg/keV 20cm self shield: ~10-5 /day/kg/keV (2events/100kg/5keV/year)

  29. Radioactive contamination Measured with the prototype detector Internal origin of background Target values to achieve our goal 238U: < 1x10-14 g/g 232Th: < 2x10-14 g/g 85Kr: < 1ppt from reactors (9±6) x10-14 g/g Further reduction by filter < 23 x10-14 g/g Upper limit, use filter 3.3±1.1 ppt Distillation system (original) U, Th, Kr near to the goal. Within reach.

  30. Sensitivity of the 800kg detector XMASS FV 0.5ton year (100kg, 5yr) 3s discovery W/O any pulse shape info. x 100 sensitive than CDMSII 106 104 102 1 10-2 10-4 103 Plots exept for XMASS http://dmtools.berkeley.edu Gaitskell & Mandic

  31. 10-6 10-8 Cross section to nucleon (pb) 10-10 10-12 Near future ~5years • Ge, Ar and Xe go down to 10-9pb • Aim to detect DM ~2010

  32. 10-6 10-8 Cross section to nucleon (pb) 10-10 10-12 +10yr, sensitivity of DM exp. <10-10pb • ~10ton volume • Thick outer shield (~30cm) will reduce neutron BG for further >100!

  33. Summary • Direct detection of DM, WIMPs, is an urgent issue. • Solid state & Noble gas liquid are the world trend for large scale experiments. • Search with <10-9pb, neutron will be most serious background, and it should be shielded by the target volume itself.  XMASS • R&D efforts for XMASS done. • XMASS at Kamioka is going to improve factor 100 in the sensitivity (~10-9pb). • Serious competition in the world. Need to start now!

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