the exo-200 double beta decay experiment and plans for the future david sinclair valday 2014
TRANSCRIPT
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The EXO-200 Double Beta Decay Experiment and Plans for the Future
David SinclairValday 2014
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The EXOCollaboratio
n
University of Alabama, Tuscaloosa AL, USA - D. Auty, T. Didberidze, M. Hughes, A. Piepke, R. TsangUniversity 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. SinclairColorado State University, Fort Collins CO, USA - C. Benitez-Medina, C. Chambers, A. Craycraft, W. Fairbank, Jr., T. WaltonDrexel University, Philadelphia PA, USA - M.J. Dolinski, M.J. Jewell, Y.H. Lin, E. SmithDuke University, Durham NC, USA – P.S. BarbeauIHEP 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. KaufmanUniversity of California, Irvine, Irvine CA, USA - M. MoeITEP Moscow, Russia - D. Akimov, I. Alexandrov, V. Belov, A. Burenkov, M. Danilov, A. Dolgolenko, A. Karelin, A. Kovalenko, A. Kuchenkov, V. Stekhanov, O. ZeldovichLaurentian University, Sudbury ON, Canada - B. Cleveland, J. Farine, B. Mong, U. WichoskiUniversity of Maryland, College Park MD, USA - C. Davis, A. Dobi, C. Hall, S. Slutsky, Y-R. YenUniversity of Massachusetts, Amherst MA, USA - T. Daniels, S. Johnston, K. Kumar, A. Pocar, D. Shy, J.D. WrightUniversity of Seoul, South Korea - D.S. LeonardSLAC 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. WittgenStanford 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. WeberTechnical University of Munich, Garching, Germany - W. Feldmeier, P. Fierlinger, M. MarinoTRIUMF, Vancouver BC, Canada – J. Dilling, R. Krucken, F. Retière, V. Strickland
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Outline of talk
• Some thoughts on double beta physics• Description of the EXO-200 Detector• Detection of 2 nbb decay in 136Xe• Limits on 0nbb decay in 136Xe• Plans for the future
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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
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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
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Assuming 3 families
AtmosphericMinosT2K
ReactorT2KMinosSolar
LBNE
SolarKAMLAND
0bb n
Pontecorvo Maki Nakagawa Sakata Matrix
(Cosmology favours about 4 but evidence is weakening)
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What do we know about mixing angles
• With good accuracy• F12 = 33.8o from solar, kamland
• F23 = 45o from SuperK, Minos…
• F13 = 9o from reactors• d CP phase not known• 1, 2 a a Majorana phases not known
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Slide from Yvonne WongTaup 2011
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OferLahav
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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
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Seesaw Model
• Neutrino masses are very small because of mR in denominator. mR is at the gut scale
• If mL is not zero it can dominate and give degenerate neutrino masses
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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
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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
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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
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Double Beta (cont.)
• G is known, scales with E5
• M is a nuclear matrix element. Calculations are converging (factor of 2)
• m2bb contains neutrino mixing information
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Nucl. Phys. B659 359
Dark areasShow variation due to phases only
Light colours include experimental errors
Assumed q13 =0
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Klapdor-Kleingrothaus Results for Ge double beta decay
57 kg years of 76Ge data Apply single site criterion
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Candidate Isotopes
Isotope Energy (keV) Abundance %76Ge 2039. 7.8136Xe 2462 8.9130Te 2530 34.582Se 2996 9.2100Mo 3035 9.6150Nd 3367 5.648Ca 4274 0.19
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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)
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Why Xenon
• Favourable Q value• Easy to make very pure• Easiest (least expensive!) isotope to produce• Possibility of background control through
tagging of daughter
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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
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The EXO-200 Detector
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Measuring Electron lifetime
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EXO-200 has achievedVery long lifetimes
Supports plans for largerDetector
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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
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Current state of sourceReproductionThere are no freeParameters except overallnormalization
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Moving on to Neutrinoless Decay
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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
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nEXO at SNOLAB
Water
Cryostat
Detector
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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
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nEXO Exclusion Limit (90% confidence 4 years)
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The Big Challenge
• The biggest challenge for the project will be securing 5 T of enriched 136Xe
• Russia is the only country that has the capability of producing such an enormous amount of isotopically separated material
• We need to look at this project as a global endeavor
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TPC or Scintillator?
• Scintillator can proceed with minor changes to existing detector
• Good self shielding from clean scintillator
• Great detector for exclusion limit
• TPC has better energy resolution (we aim for 1%)
• TPC gives more handles to discriminate against backgrounds
• Probably better ability to make discovery
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Can we reach the normal hierarchy?
• Need to control even better the backgrounds• We may be able to tag events with the
production of 136Ba• Process involves extraction of the Ba ion from
xenon, trapping it, and identification by laser spectroscopy
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Barium tagging
2P1/2
4D3/2
2S1/2
493nm
650nm
metastable 80s
Requires Ba+ ion
Double beta decay produces Ba++
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Extraction of Ions from gas
• Test process using atmospheric pressure electrospray source and a quadrupole mass spec
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Conversion from Ba++ to Ba+
• Pass ions through low pressure TEA• TEA has low IP and can give up an electron to
Ba++ but not to Ba+• Use triple quadrupole system. First quad
selects Ba++, second contains the TEA, third analyses the products
• Conversion efficiency looks very high and no evidence for molecular formation
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Timescale for Next Phase
• EXO is taking 0 neutrino search data now• Will probably reach background limit in couple
of years• DOE has indicated it wants to make a decision
on next generation detector in ~ 2 years• We need to have a developed proposal on this
timescale