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The EXO-200 Double Beta Decay Experiment and Plans for the Future

The EXO-200 Double Beta Decay Experiment and Plans for the Future. David Sinclair Valday 2014. The EXO Collaboration. University of Alabama, Tuscaloosa AL, USA - D. Auty, T. Didberidze, M. Hughes, A. Piepke, R. Tsang

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The EXO-200 Double Beta Decay Experiment and Plans for the Future

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  1. The EXO-200 Double Beta Decay Experiment and Plans for the Future David Sinclair Valday 2014

  2. The EXO Collaboration University of Alabama, Tuscaloosa AL, USA - D. Auty, T. Didberidze, M. Hughes, A. Piepke, R. Tsang University of Bern, Switzerland - S. Delaquis, G. Giroux, R. Gornea, T. Tolba, J-L. Vuilleumier California Institute of Technology, Pasadena CA, USA - P. Vogel Carleton University, Ottawa ON, Canada - V. Basque, M. Dunford, K. Graham, C. Hargrove, R. Killick, T. Koffas, F. Leonard, C. Licciardi, M.P. Rozo, D. Sinclair Colorado State University, Fort Collins CO, USA - C. Benitez-Medina, C. Chambers, A. Craycraft, W. Fairbank, Jr., T. Walton Drexel University, Philadelphia PA, USA - M.J. Dolinski, M.J. Jewell, Y.H. Lin, E. Smith Duke University, Durham NC, USA – P.S. Barbeau IHEP Beijing, People’s Republic of China - G. Cao, X. Jiang, L. Wen, Y. Zhao University of Illinois, Urbana-Champaign IL, USA - D. Beck, M. Coon, J. Ling, M. Tarka, J. Walton, L. Yang Indiana University, Bloomington IN, USA - J. Albert, S. Daugherty, T. Johnson, L.J. Kaufman University of California, Irvine, Irvine CA, USA - M. Moe ITEP Moscow, Russia - D. Akimov, I. Alexandrov, V. Belov, A. Burenkov, M. Danilov, A. Dolgolenko, A. Karelin, A. Kovalenko, A. Kuchenkov, V. Stekhanov, O. Zeldovich Laurentian University, Sudbury ON, Canada - B. Cleveland, J. Farine, B. Mong, U. Wichoski University of Maryland, College Park MD, USA - C. Davis, A. Dobi, C. Hall, S. Slutsky, Y-R. Yen University of Massachusetts, Amherst MA, USA - T. Daniels, S. Johnston, K. Kumar, A. Pocar, D. Shy, J.D. Wright University of Seoul, South Korea - D.S. Leonard SLAC National Accelerator Laboratory, Menlo Park CA, USA - M. Breidenbach, R. Conley, A. Dragone, K. Fouts, R. Herbst, S. Herrin, A. Johnson, R. MacLellan, K. Nishimura, A. Odian, C.Y. Prescott, P.C. Rowson, J.J. Russell, K. Skarpaas, M. Swift, A. Waite, M. Wittgen Stanford University, Stanford CA, USA - J. Bonatt, T. Brunner, J. Chaves, J. Davis, R. DeVoe, D. Fudenberg, G. Gratta, S.Kravitz, D. Moore, I. Ostrovskiy, A. Rivas, A. Schubert, D. Tosi, K. Twelker, M. Weber Technical University of Munich, Garching, Germany - W. Feldmeier, P. Fierlinger, M. Marino TRIUMF, Vancouver BC, Canada – J. Dilling, R. Krucken, F. Retière, V. Strickland

  3. Outline of talk • Some thoughts on double beta physics • Description of the EXO-200 Detector • Detection of 2nbb decay in 136Xe • Limits on 0nbb decay in 136Xe • Plans for the future

  4. 2 Neutrino Double Beta Decay • Nemo has done a great job of measuring most of the 2 neutrino double beta decay rates • 136Xe is an exception because NEMO cannot use a gas source • Earlier work suggested limits on the 136Xe rate which would make it exceptionally slow

  5. Physics of double beta decay • Understanding Neutrinoless DBD is closely coupled to understanding neutrino masses and mixing • We therefore make a diversion to look at what we know

  6. Assuming 3 families (Cosmology favours about 4 but evidence is weakening) Pontecorvo Maki Nakagawa Sakata Matrix LBNE Atmospheric Minos T2K Reactor T2K Minos Solar Solar KAMLAND bb 0n

  7. What do we know about mixing angles • With good accuracy • F12 = 33.8ofrom solar, kamland • F23 = 45o from SuperK, Minos… • F13= 9o from reactors • d CP phase not known • a1, a2 Majorana phases not known

  8. Slide from Yvonne Wong Taup 2011

  9. Ofer Lahav

  10. Neutrino mass in the Standard Model • In the standard model neutrino masses are 0 • Because we only observe left handed neutrinos we cannot form a Dirac mass term this way • Possible to form a Majorana mass term

  11. Seesaw Model • Neutrino masses are very small because of mR in denominator. mRis at the gut scale • If mL is not zero it can dominate and give degenerate neutrino masses

  12. Neutrinos and Leptogenesis • The only neutrinos which can impact the baryon asymmetry are the very heavy right handed neutrinos • We would like to understand CP violation in this sector • This is far beyond the reach of experimental physics • May be related to CP violation in light sector • See e.g. Pascoli, Petcov and Riotto, CERN-PH-TH/2006-213 • This can come from either Dirac CP term d or from the Majorana phases a or both

  13. What would we like to learn about neutrinos • Determine the mass hierarchy critical • Determine d • Are neutrinos Majorana • Determine the a parameters • Show violation of total lepton number

  14. Neutrino-less double beta decay • Observation of neutrino-less double beta decay would • Demonstrate that neutrinos are Majorana particles • Demonstrate DL=2 total lepton number violating process • Set mass scale for the neutrino • Rate is given by

  15. Double Beta (cont.) • G is known, scales with E5 • M is a nuclear matrix element. Calculations are converging (factor of 2) • m2bbcontains neutrino mixing information

  16. Nucl. Phys. B659 359 Dark areas Show variation due to phases only Light colours include experimental errors Assumed q13 =0

  17. Klapdor-Kleingrothaus Results for Ge double beta decay 57 kg years of 76Ge data Apply single site criterion

  18. Candidate Isotopes

  19. EXO 200 • Tracking Liquid TPC • 200 kg enriched 136Xe • Ionization + scintilation • No gain in ionization channel – demanding on electronics • Lead shield + HFE (heat transfer fluid)

  20. Why Xenon • Favourable Q value • Easy to make very pure • Easiest (least expensive!) isotope to produce • Possibility of background control through tagging of daughter

  21. What form to use? • Gas (eg NEXT, Gotthard) • Excellent energy resolution • Good tracking • Detector is large so shielding is more challenging • Liquid Scintillator • Refer to Kozlov’s talk • Liquid Xenon • Compact, reasonable resolution, event reconstruction

  22. The EXO-200 Detector

  23. Measuring Electron lifetime

  24. EXO-200 has achieved Very long lifetimes Supports plans for larger Detector

  25. New Analysis out this week • After a lot of work to fully understand the detector response a more precise value has been obtained. • T1/2 = 2.172 +-0.017 (stat) +-0.060 (syst)x1021 y • Most precisely measured 2 neutrino double beta decay rate to date • Possible because of the homogeneous detector design • URL: http://link.aps.org/doi/10.1103/PhysRevC.89.015502 • DOI: 10.1103/PhysRevC.89.015502

  26. Current state of source Reproduction There are no free Parameters except overall normalization

  27. Moving on to NeutrinolessDecay

  28. EXO Future • Next step will be nEXO • 5 T liquid xenon enriched in 136Xe • Location likely to be SNOLAB • 5T is chosen as the mass required to cover the inverted hierarchy • Replace lead with large water shield

  29. nEXO at SNOLAB Water Cryostat Detector

  30. Some changes from EXO-200 • Need internal electronics to cut noise • Have to deal with heat • Go to single ended TPC design to give maximum self-shielded fiducial mass

  31. nEXO Exclusion Limit (90% confidence 4 years)

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