neutrinoless double beta decay with exo-200 and nexo · neutrinoless double beta decay with ......
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Michelle Dolinski!Drexel University!22 October 2015!
Neutrinoless double beta decay with EXO-200 and nEXO!
What we know about neutrinos
• Is there CP violation in the neutrino sector?!• Do neutrino masses follow the normal hierarchy or the inverted hierarchy?!• What is the absolute mass scale?!• What is the quantum nature of the neutrino? Dirac vs. Majorana…!
NH IH
mee! Σ mi
2
Double beta decay
0νββ can only occur for nonzero Majorana neutrino mass term!!
M.G
oepp
ert-M
ayer
,!Ph
ys. R
ev. 4
8 (1
935)
512!
2νββ
0νββ
2νββ spectrum!(normalized to 1)!
0νββ peak!(normalized to 10-6)!
0νββ peak!(normalized to 10-2)!
G0ν is a phase space factor ∝ Q 5!M0ν is the nuclear matrix element!T1/2
0ν!" #$−1=G0ν ∗ M 0ν 2
∗ mββ
2
Nuclear matrix elements
V.A. Rodin, A. Faessler, F. Simkovic, and P. Vogel, Phys. Rev. C 68, 044302 (2003);!V.A. Rodin, A. Faessler, F. Simkovic, and P. Vogel, Nucl. Phys. A 793, 213 (2007), and erratum A 793, 213 (2007).!Dong-Liang Fang, A. Faessler, V. Rodin, F. Simkovic, Phys. Rev. C 82, 051301 (2010);.!F. Simkovic Phys.Part.Nucl. 42 (2011) 598.!T.R. Rodriguez, G. Martinez-Pinedo, Prog.Part.Nucl.Phys. 66 (2011) 436.!T.R. Rodr+gez and G. Martinez-Pinedo, Phys. Rev. Lett. 105, 252503 (2010).!P.K. Rath, R. Chandra, K. Chaturvedi, P.K. Raina, J.G. Hirsch, Phys. Rev. C 82, 064310 (2010); P.K. Rath J.Phys.Conf.Ser. 322 (2011) 012019.!J. Barea, F. Iachello, Phys. Rev. C 79, 044301 (2009); !F. Iachello, J. Barea, Nucl.Phys.Proc.Suppl. 217 (2011) 5; !F. Iachello, J. Barea, AIP Conf.Proc. 1355 (2011) 7.!J. Menendez, A. Poves E. Caurier, F. Nowacki J.Phys.Conf.Ser. 312 (2011) 072005;!J. Menendez, A. Poves, E. Caurier, and F. Nowacki, Nucl. Phys. A 818, 139 (2009).!
Bilenky and Giunti, arXiv:1203.5250v1!
!!
Need to observe 0νββ in multiple isotopes!!
T1/20ν!" #$
−1=G0ν ∗ M 0ν 2
∗ mββ
2
4
Using the standard representation of the PNMS matrix, the effective Majorana neutrino mass is given as:!
( ) ( )( ) ( )
3
12
αi13
23
ααi13
212
22
132
122
1ββ
eθsinm
eθsin1θsinm
θsin1θsin1mm
⋅−
−⋅
⋅⋅
+⋅−⋅⋅
+−⋅−⋅=
The three CP phases α1, α2, and α3 are unknown. This uncertainty is expressed by varying:!
( ) ( ) ( ) ( )( ) 13
232
132
122
21132
122
1ββ
θsinm
θsin1θsinmθsin1θsin1mm
⋅±
−⋅⋅±−⋅−⋅=
T1/20ν!" #$
−1=G0ν ∗ M 0ν 2
∗ mββ
2
Effective Majorana mass
5
Now we insert the standard neutrino oscillation parameters (central values). No total cancellation is possible for the inverted hierarchy.!!!Plots courtesy Andreas Piepke.!
Inverted hierarchy
6
Once one of the CP phases is allowed to become negative the mass becomes negative, introducing the characteristic discontinuity into the absolute value of the mass.
For the normal hierarchy variation of the unknown CP-phases introduces: 1) considerable
variation of the effective mass,
2) allows destructive interference for certain values of mmin and choice of phases.
Normal hierarchy
7
Combined phase space
Inverted and normal hierarchy including 3σ errors on oscillation parameters.!
8
Claim for observation of 0νββ Fit model:! 6 gaussians + linear bknd.!!Fitted excess @ Qββ ! 28.75 ± 6.86 → 4.2 σ!!!!!!![H.V.Klapdor-Kleingrothaus ! and I.Krivosheina, ! Mod.Phys.Lett. A21 (2006) 1547]!
T1/2 = 2.23−0.31+0.44 ⋅1024 yr
mββ = 0.32± 0.03 eV
76Ge Q-value!
???!
214Bi!214Bi!
Heidelberg-Moscow Collaboration split over this result, and it is still
controversial.!9
Sensitivity of DBD experiments
• Large mass!• High isotopic abundance!• Good energy resolution!• High efficiency!• Low background!
For the source = detector configuration:!!!!!f is the number of atoms of the ββ isotope/molecule; !A is the molecular mass; !M is the mass; !t is the running time; !B is the number of background counts/keV/kg/year; !ΔE is the energy resolution of the detector in keV;!ε is the detector efficiency in the ββ region!
€
F0ν = ln 2 ⋅ NAfA
MtBΔE%
& '
(
) * 1/2
ε
KamLAND-Zen!
10
Why Xe?!• Q-value of 2458 keV [Redshaw et al., PRL 98, 053003 (2007)] gives favorable phase space and a 0νββ region of interest above most naturally occurring γ-rays.!• Natural isotopic abundance of 8.9% with inexpensive enrichment.!• Noble gas/liquid detector allows continuous purification.!• Possibility of tagging the Ba+ daughter ion.!
EXO-200 and nEXO are part of a program to search for the decay 136Xe → 136Ba++ + 2e-!
Ultimate goal is a tonne scale detector with real time Ba+ tagging and sensitivity to mββ of ~10 meV.!
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EXO-200Liquid Xe TPC!
~100 kg fiducial mass Xe enriched to 80% in 136Xe, ultralow background construction.!
Readout plane is made up of LAAPDs + crossed wire grid.! 12
University of Alabama, Tuscaloosa AL, USA — D Auty, T Didberidze, M Hughes, A Piepke, R Tsang!University of Bern, Switzerland — S Delaquis, R Gornea†, J-L Vuilleumier !†Now at Carleton University!University of California, Irvine, Irvine CA, USA — M Moe!California Institute of Technology, Pasadena CA, USA — P Vogel!Carleton University, Ottawa ON, Canada — M Dunford, R Gornea, K Graham, C Hargrove, R Killick, T Koffas, C Licciardi, D Sinclair!Colorado State University, Fort Collins CO, USA — C Chambers, A Craycraft, W Fairbank Jr., T Walton!Drexel University, Philadelphia PA, USA — MJ Dolinski, YH Lin, E Smith, Y-R Yen, T Winick!Duke University, Durham NC, USA — PS Barbeau!IBS Center for Underground Physics, Daejeon, South Korea — DS Leonard!IHEP Beijing, People’s Republic of China — G Cao, W Cen, L Wen, J Zhao!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!University of Illinois, Urbana-Champaign IL, USA — D Beck, M Coon, J Walton, L Yang!Indiana University, Bloomington IN, USA — JB Albert, S Daugherty, TN Johnson, LJ Kaufman, J Zettlemoyer!Laurentian University, Sudbury ON, Canada — B Cleveland, A DerMesrobian-Kabakian, J Farine, B Mong, U Wichoski!University of Maryland, College Park MD, USA — C Hall!University of Massachusetts, Amherst MA, USA — S Feyzbakhsh, S Johnston, J King, A Pocar!McGill University, Montreal PQ, Canada — T Brunner!SLAC National Accelerator Laboratory, Menlo Park CA, USA — M Breidenbach, R Conley, T Daniels, J Davis, A Dragone, K Fouts, R Herbst, A Johnson, M Kwiatkowski K Nishimura, A Odian, CY Prescott, PC Rowson, JJ Russell, K Skarpaas, A Waite, M Wittgen!University of South Dakota, Vermillion SD, USA — R MacLellan!Stanford University, Stanford CA, USA — R DeVoe, D Fudenberg, G Gratta, M Jewell, S Kravitz, D Moore, I Ostrovskiy, A Schubert, K Twelker, M Weber!Stony Brook University, SUNY, Stony Brook, NY, USA — K Kumar, O Njoya, M Tarka!Technical University of Munich, Garching, Germany — W Feldmeier, P Fierlinger, M Marino!TRIUMF, Vancouver BC, Canada — J Dilling, R Krücken, F Retière, V Strickland!
The
EX
O-2
00 C
olla
bora
tion
EXO-200 @ WIPP EXO-200 is sited at the Waste Isolation Pilot Plant (WIPP) in Carlsbad, NM, a DOE facility for the disposal of radioactive waste. Provides ~1600 m.w.e. shielding and low U, Th, and Rn.!• TPC housed in thin-walled copper vessel.!• Vacuum insulated cryostat with HFE-7000 for shielding and thermal bath.!• Lead shield.!• Clean room environment.!• Active muon veto.!• Other support systems not shown here (refrigeration, gas handling, etc.).!Operated with enriched Xe from May 2011 to Feb. 2014.!! 15
Anti-correlation of charge and light!Energy measurement!
• Rotation angle determined weekly using 228Th source data, defined as angle which gives best rotated resolution!
• Energy resolution is dominated by APD noise! 16
APD Denoising!Problem: Resolution is dependent on the time-varying correlated noise of the APDs!Software solution (current): Find the optimum combination of APD signals per event, given position and noise!Hardware solution (future): Planned upgrade of APD readout electronics to reduce noise!
Resolution curve from simulation using NEST: http://nest.physics.ucdavis.edu/!
at 2
615
keV
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• Event with 1 charge cluster: single-site events!
• Events with > 1 charge cluster: multi-site events !
Allows for background measurement and reduction!
0νββ: ~90% SS!!
γ-rays: ~30% SS at 0νββ Q-value!
Position and multiplicity reconstruction!
Total error in fiducial volume from position reconstruction: 1.73%!18
Single site 232Th Probability Density Function in copper vessel!
• Variables!• Energy!• Position
(standoff distance)!• Multiplicity!
• SS!• MS!
Background model! Data! Physics Results!+!Maximum!
Likelihood Fit!
Extracting physics results!
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2νββ precision measurement!
Most precise measurement of the 2νββ half-life T1/2
2νββ = 2.165 ± 0.016(stat) ± 0.059(sys) × 1021 yr [PRC 89, 015502 (2014)]!
2νββ signal to background !ratio: !11: 1!!Inner 40% fiducial volume signal to background ratio:!19: 1!
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Single site!
Multi site!
!!0νββ search! Analysis range: !980 keV to 9800 keV!
100 kg⋅yr !736 mol⋅yr 136Xe exposure
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0νββ search results!
Profi
le li
kelih
ood!T1/2
0νββ > 1.1 x 1025 yr!〈mββ〉 < 190 – 450 meV
(90% C.L.)
[Nature 510, 229 (2014)]! 22
Backgrounds in the ROI!
30% reduction of background index in inner 40% fiducial volume!
consistent with previous result ![PRL 109, 032505 (2012)]!
Shrinking fiducial volume!
Backgrounds in ± 2σ R.O.I.!
Th-228 chain! 16.0!
U-232 chain! 8.1!
Xe-137! 7.0!
Total! 31.1 ± 3.8!
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Comparing experiments!
EXO-200 sensitivity (90%CL):!1.9 x 1025 yr!!EXO-200 limit (90%CL):!1.1 x 1025 yr!
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Other recent papers!
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Measurements of the ion fraction and mobility of alpha and beta decay products in liquid xenon using EXO-200, arXiv:1506.00317!!Investigation of radioactivity-induced backgrounds in EXO-200, Phys. Rev. C 92 015503 (2015), arXiv:1503.06241!!Search for Majoron-emitting modes of double-beta decay of 136Xe with EXO-200, Phys. Rev. D 90, 092004 (2014), arXiv:1409.6829!
Experimental outlook!
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An external review of the EXO project was conducted on June 1, 2 2015 at SLAC. The purpose of the review was to assess the scientific potential of further operations, the technical readiness of the detector and the cost and arrangements at the WIPP site. We find that the scientific potential for an additional three years of running the EXO-200 detector remains strong and that the collaboration has already made significant progress towards the restart.!
EXO-200 sensitivity outlook!
EXO-200 ultimate
EXO-200 Nature 2014
EXO-200 current sensitivity (90%CL):!1.9 x 1025 yr!!EXO-200 ultimate sensitivity (90%CL): 3 years additional running with improved energy resolution and Rn removal!
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nEXO!
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14 m
Φ 13 m 5 tonne “conventional” low background LXe detector, possibly sited at SNOLAB.!
Option to include Ba+ tagging…!
University of Alabama, Tuscaloosa AL, USA — T Didberidze, M Hughes, A Piepke, R Tsang!University of Bern, Switzerland — S Delaquis, R Gornea†, J-L Vuilleumier ! !†Now at Carleton University!Brookhaven National Laboratory, Upton NY, USA — M Chiu, G De Geronimo, S Li, V Radeka, T Rao, G Smith, T Tsang, B Yu!California Institute of Technology, Pasadena CA, USA — P Vogel!Carleton University, Ottawa ON, Canada — Y Baribeau, V Basque, M Bowcock, M Dunford, M Facina, R Gornea, K Graham, P Gravelle, R Killick, T Koffas, C Licciardi, K McFarlane, R Schnarr, D Sinclair!Colorado State University, Fort Collins CO, USA — C Chambers, A Craycraft, W Fairbank Jr., T Walton!Drexel University, Philadelphia PA, USA — MJ Dolinski, YH Lin, E Smith, T Winick, Y-R Yen!Duke University, Durham NC, USA — PS Barbeau, G Swift!University of Erlangen-Nuremberg, Erlangen, Germany — G Anton, R Bayerlein, J Hoessl, P Hufschmidt, A Jamil, T Michel, T Ziegler!IBS Center for Underground Physics, Daejeon, South Korea — DS Leonard!IHEP Beijing, People’s Republic of China — G Cao, W Cen, X Jiang, H Li, Z Ning, X Sun, T Tolba, W Wei, L Wen, W Wu, J Zhao!University of Illinois, Urbana-Champaign IL, USA — D Beck, M Coon, J Walton, L Yang!Indiana University, Bloomington IN, USA — JB Albert, S Daugherty, TN Johnson, LJ Kaufman, G Visser, J Zettlemoyer!University of California, Irvine, Irvine CA, USA — M Moe!ITEP Moscow, Russia — V Belov, A Burenkov, M Danilov, A Dolgolenko, A Karelin, A Kobyakin, A Kuchenkov, V Stekhanov, O Zeldovich!Laurentian University, Sudbury ON, Canada — B Cleveland, A Der Mesrobian-Kabakian, J Farine, B Mong, U Wichoski!Lawrence Livermore National Laboratory, Livermore CA, USA — O Alford, J Brodsky, M Heffner, G Holtmeier, A House, M Johnson, S Sangiorgio!University of Massachusetts, Amherst MA, USA — J Dalmasson, S Feyzbakhsh, S Johnston, J King, A Pocar!McGill University, Montreal PQ, Canada — T Brunner!Oak Ridge National Laboratory, Oak Ridge TN, USA — L Fabris, D Hornback, RJ Newby, K Ziock!Rensselaer Polytechnic Institute, Troy NY, USA — E Brown!SLAC National Accelerator Laboratory, Menlo Park CA, USA — T Daniels,- K Fouts, G Haller, R Herbst, M Kwiatkowski, K Nishimura, A Odian, M Oriunno, PC Rowson, K Skarpaas!University of South Dakota, Vermillion SD, USA — R MacLellan!Stanford University, Stanford CA, USA — R DeVoe, D Fudenberg, G Gratta, M Jewell, S Kravitz, D Moore, I Ostrovskiy, A Schubert, K Twelker, M Weber!Stony Brook University, SUNY, StonyBrook, NY, USA — K Kumar, O Njoya, M Tarka!Technical University of Munich, Garching, Germany — P Fierlinger, M Marino!TRIUMF, Vancouver BC, Canada — J Dilling, P Gumplinger, R Krücken, F Retière, V Strickland!!
The
nEX
O C
olla
bora
tion
EXO-200 to nEXO!
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nEXO is a large, homogenous detector
that builds on the success of EXO-200.
nEXO R&D program!
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TPC E-field simulations: SiPMs: HV testing setup:
Charge readout cell:
1. High Voltage !!2. Photodetectors !!3. Low background, cryogenic electronics!4. Novel, low background TPC concepts!5. Calibration concepts !!6. Low background vessels !!7. Radiopurity investigations !!8. Simulation ! !!
EXO-200 to nEXO!
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The size of the detector allows us to take
advantage of Compton scattering to measure external backgrounds
precisely.
nEXO simulation!
33 nEXO 5 year sensitivity of 6.6x1027 years
nEXO Background measurement!
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35
nEXO sensitivity – worst case NME!
nEXO sensitivity – best case NME!
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nEXO sensitivity outlook!
EXO-200 ultimate
EXO-200 Nature 2014 nEXO 5 year sensitivity (90%CL):!6.6 x 1027 yr!
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nEXO 5 year
nEXO 5 year with Ba tagging
What next? Let’s assume we see it…!The next generation of neutrinoless double beta decay experiments may detect 0νββ at mass scales of mββ ~100 meV. If they do, precision experiments to nail down the nuclear physics and the mechanism!!
• First, precision measurements in multiple isotopes to nail down the nuclear physics.!• Angular correlations to try to understand the mechanism – Low pressure gas TPC or NEMO-like experiment to study angular correlations. Need lots of decays, so this is hard.!• Mechanism would be further constrained by observation of neutrinoless EC/β+ or double EC.!• Finally, Majorana phases?? (Not likely!)!
!But if we rule out the IH…!Need excellent energy resolution, heroic background rejection, and ~10 tons or more of enriched isotope.! 38
Conclusions!
• Neutrinoless double beta decay, the most practical way to test the Majorana nature of neutrinos, is an important part of the neutrino physics program.!
• EXO-200 first observed 136Xe 2νββ and set a lower limit on the 0νββ half-life [Nature 510, 229 (2014)]!
T1/20νββ (136Xe) > 1.1 x 1025 yr (90% C.L.)!
!with a corresponding limit on Majorana neutrino mass of!mν < 190 - 450 meV (90% C.L.)!
• The next generation nEXO experiment is poised to test effective Majorana masses down to the ~10 meV scale.!
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