Pushing the Limits: Dark Matter Search with SuperCDMS. Wolfgang Rau Queen s University Kingston For the SuperCDMS Collaboration

Transcription

1 Pushing the Limits: Dark Matter Search with Wolfgang Rau Queen s University Kingston For the Collaboration

2 Dark Matter Velocity Observed Zwicky Expected (Kepler) Radius Rubin Luminous Matter (< 1 %) Ordinary Matter (~ 4 %) Dark Energy (>70 %) Dark Matter (~23 %) CMB

3 Dark Matter Here, but not yet observed in nature: Weakly interacting WIMP (Weakly Interacting Massive Particle) Not observed in accelerator experiments: Massive Large scale structure of the Universe: Slowly moving ( cold ) Predicted by SUSY: Neutralino Universal extra dimensions: Kaluza-Klein particles

4 W. Rau at SNOLAB May 2012 Overview 4 Dark Matter Detection Technology Results Conclusions

5 W. Rau at SNOLAB May 2012 Dark Matter Detection Landscape and Background 5 Dark Matter Sensitivity (pb) Background free 1 event /kg/d 1 event /t /7d 10 kg y 1 t y 5/t/y Sensitivity (cm 2 ) Results Conclusion Exposure (kg d)

6 W. Rau at SNOLAB May 2012 / Collaboration 6 California Institute of Technology Z. Ahmed, S.R. Golwala, D. Moore, R. Nelson Fermi National Accelerator Laboratory D. A. Bauer, J. Hall, D. Holmgren, L. Hsu, B. Loer, R.B. Thakur Massachusetts Institute of Technology A. J. Anderson, E. Figueroa-Feliciano, S.A. Hertel, S.W. Leman, K.A. Mccarthy NIST K. Irwin Queen s University C.H. Crewdson, P. C.F. Di Stefano, J. Fox, O. Kamaev, C. Martinez, P. Nadeau, K. Page, W. Rau, Y. Ricci, M.-A. Verdier Santa Clara University B. A. Young SLAC/KIPAC M. Asai, A. Borgland, D. Brandt, P.L. Brink,, E. Do Couto E Silva, G.L. Godrey, J. Hasi, M. Kelsey, C. J. Kenney, P. C. Kim, M.E. Monzani, R. Partridge, R. Resch, D. Wright Southern Methodist University J. Cooley, B. Karabuga, H. Qiu, S. Scorza Stanford University B. Cabrera, R. Moffat, M. Pyle, P. Redl, B. Shank, S. Yellin, J. Yen Syracuse University R. Bunker, Y. Chen, M.. Kiveni, R. W. Schnee Texas A&M R. Harris, A. Jastram, K. Koch, R. Mahapatra, J. Sander University of California, Berkeley M. Daal, T. Doughty, N. Mirabolfathi, A. Phipps, B. Sadoulet, B. Serfass, D. Speller, K.M. Sundqvist University of California, Santa Barbara D.O. Caldwell University of Colorado Denver M.E. Huber University of Florida R. Agnese, D. Balakishiyeva, T. Saab, B. Welliver Universidad Autonoma de Madrid D. Credeño, L. Esteban University of Minnesota H. Chagani, J. Beaty, P. Cushman, S. Fallows, M. Fritts, T. Hofer, V. Mandic, R. Radpour, A. Reisetter, A. Villano, J.Zhang University of Zurich S. Arrenberg, T. Bruch, L. Baudis Dark Evidence Matter Results Conclusion

7 W. Rau at SNOLAB May 2012 Technology Operating Principle 7 Phonon signal Charge signal Thermal bath Electron recoil Thermal coupling e + - n Target Phonon sensor Nuclear recoil Phonon signal: measures energy deposition Ionization signal: quenched for nuclear recoils (lower signal efficiency) Allows us to distinguish potential signal from background Ionization energy [kev eeq] Electron recoils from β s and γ s Nuclear recoils from neutrons Dark Evidence Matter Results Conclusion Phonon energy [kev]

8 W. Rau at SNOLAB May 2012 Cryogenic ionization detectors, Ge (Si) = 7 cm, h = 1 cm, m = 250 g (100 g) Technology Detectors Thermal readout: superconducting phase transition sensor (TES) Transition temperature: mk 4 sensors/detector, fast signal (< ms) Charge readout: Al electrode, divided 8 Dark Evidence Matter Results Conclusion

9 W. Rau at SNOLAB May 2012 Technology Detector Performance 9 Ionization/Recoil energy Ionization/Recoil energy γ-band n-band Recoil energy [kev] γ-band β-band n-band Z -sensitive I onization and P honon detectors surface event rising edge slope nuclear recoil γs βs neutrons Dark Evidence Matter Results Conclusion Recoil energy [kev]

10 W. Rau at SNOLAB May 2012 The Family I 6 detectors 1 kg Ge (30 kgd ) σ < 3.5e-42 cm SUF, 10 mwe 2 Soudan, 2100 mwe exposures are after all cuts! SNOLAB, 6000 mwe II 30 detectors ~4 kg Ge (400 kgd) σ < 3.5e-44 cm Soudan 15 detectors 10 kg Ge (~2500 kgd) σ < 5e-45 cm SNOLAB detectors 100 kg Ge (~35000 kgd) σ < 2e-46 cm test SNOLAB (2011) Dark Evidence Matter Results Conclusion

11 W. Rau at SNOLAB May 2012 at Soudan Experimental Setup 11 Tower (6 Detectors) Cryostat, Coldbox Shielding Soudan Underground lab (2000 m w.e.) 5 Towers (~ 5 kg Ge ) operated Dark Evidence Matter Results Conclusion

12 W. Rau at SNOLAB May 2012 Results Spin independent interaction 12 Dark Matter Data EDELWEISS 2009 XENON Dark Evidence Matter Results Conclusion

13 W. Rau at SNOLAB May 2012 Results Spin independent interaction 13 CRESST EDELWEISS II 2011 XENON d CRESST EDELWEISS Dark Evidence Matter Results Conclusion

14 W. Rau at SNOLAB May 2012 DAMA/CoGeNT Low Mass WIMPs? 14 Evidence: DAMA: annual oscillation signal CoGeNT: Exponential rate increase at low energy Both have an interpretation as low mass WIMP (< 10 GeV) signal Sun Erde Dark Evidence Matter Results Conclusion

15 W. Rau at SNOLAB May 2012 DAMA/CoGeNT Low Mass WIMPs? 15 Evidence: DAMA: annual oscillation signal CoGeNT: Exponential rate increase at low energy Both have an interpretation as low mass WIMP (< 10 GeV) signal Data What can we () do? Lower Threshold Background increases BUT: expected WIMP rate shoots up dramatically WIMP Recoil Spectrum Dark Evidence Matter Results Conclusion Low energy extension Standard analysis range

16 W. Rau at SNOLAB May 2012 Low Threshold Analysis SUF and Soudan 16 Stanford Data Soudan Data Low mass WIMPs deposit little energy Study data below discrimination threshold Significant background: understood, but not subtracted Competitive sensitivity Stanford Underground Facility: early run (2001/02): very low noise, low trigger threshold (sub kev) Soudan: lower background, but slightly higher threshold (2 kev) New method of finding limit for multiple detectors with different background performance (Yellin) Dark Evidence Matter Results Conclusion

17 W. Rau at SNOLAB May 2012 Results Low mass WIMPs 17 Soudan 10 kev XENON 100 DAMA PICASSO CoGeNT, SUF CoGeNT interpretation by Hooper et al. Recent CoGeNT reanalysis moved region down considerably (now avoids tension with data) Dark Evidence Matter Results Conclusion

18 W. Rau at SNOLAB May 2012 Annual Modulation Analysis kev nr data CoGeNT Test hypothesis that CoGeNT modulation is caused by nuclear recoils from a setupindependent source (such as dark matter) Need to convert energy scale (CoGeNT measures ionization only; uses phonon signal to determine energy) Dark Evidence Matter Results Conclusion

19 W. Rau at SNOLAB May 2012 Annual Modulation Analysis 19 Nuclear Recoil Hypothesis inconsistent with data What if it is Electron Recoils? Would need to go to lower energy (work in progress; checking down to 2 kev is conceivable) Dark Evidence Matter Results Conclusion

20 W. Rau at SNOLAB May 2012 Soudan 20 Electric Basic field configuration calculation +2 V 0 V Phonon sensors on top and Larger mass per module: ~240 g ~600 g bottom Increased thickness improved bulk/surface ratio Dark Evidence Matter Results Conclusion -2 V 0 V Improved sensor design for better event reconstruction / surface event rejection ZIP with interleaved electrodes: izip

21 W. Rau at SNOLAB May 2012 Soudan 21 New detectors tested underground DAQ adjusted to new requirements Increase total target mass (~10 kg) Detectors cold since November; started collecting dark matter data Improve sensitivity by ~ x Pb source 34,000 betas 0 events leakage Surface events Dark Evidence Matter Results Conclusion Expect limitation from cosmogenic background after 2-3 years of operation

22 log (Muon flux [m -2 s -1 ]) W. Rau at SNOLAB May 2012 Move to SNOLAB Less Cosmic radiation Cleaner environment Good Lab infrastructure CFI proposal submitted Concurrent proposals in US (DOE, NSF) Shileding [mwe] SNOLAB - Setup Setup at SNOLAB Detector volume holds ~ 150 kg of active target Pb/Cu shielding against external radiation PE shielding against neutrons Neutron detector (monitor internal n flux, veto neutrons interacting in Ge detectors) 22 Dark Evidence Matter Results Conclusion

23 Motivation Detector Test Facility Underground at SNOLAB Discrimination power required for 100 kg scale (or larger) experiments cannot be tested above ground (accidental neutron interaction rate too high) Detector modules larger than present detectors are desirable but may not be testable above ground (pile-up) Background from contamination of detectors cannot be measured above ground SUF cryostat being upgraded; installation planned in 2012 Ionization yield W. Rau at SNOLAB May 2012 Mostly neutron background Water Cryostat shield 23 Dark Evidence Matter Results Conclusion Recoil energy [kev] Sketch of Underground detector Testing Facility at SNOLAB

24 W. Rau at SNOLAB May 2012 at SNOLAB 24 Dark Evidence Matter Results Conclusion Ladder Lab Tentative Layout

25 W. Rau at SNOLAB May Conclusion Strong observational evidence for the existence of dark matter WIMPs are probably the best motivated candidates uses cryogenic semiconductor detector to search for WIMP interactions has provided best sensitivities for most of the past decade and continues to be among the top players So far no evidence for WIMPs has been found Low Threshold Analysis in tension with low-mass WIMP interpretation of DAMA and CoGeNT; no evidence for annual modulation in data at Soudan (~10 kg, izip detectors) being commissioned Will be limited by cosmogenic background after 2-3 years Planning kg setup for SNOLAB Underground test facility under construction; commissioning in 2012 Dark Matter Results Conclusion