1. The Biochemistry of 136 Xe David Nygren University of Texas at Arlington 15 December 2014Paris TPC - 20141

2.  decay: Rare transition between same A nuclei –Energetically allowed for some even-even nuclei (Z,A) → (Z+2,A) + e - 1 + 1 + e - 2 + 2 (Z,A) → (Z+2,A) + e - 1 + e - 2 (Z,A) → (Z+2,A) + e - 1 + e - 2 +  15 December 20142

3. Paris TPC - 2014 Two Types of Double Beta Decay If this process is observed: Neutrino mass ≠ 0 Neutrino = Anti-neutrino! Lepton number is not conserved! Neutrinoless double beta decay lifetime Neutrino effective mass A known standard model process and an important calibration tool Z 0  2  15 December 20143

4. Paris TPC - 2014 Two Types of Double Beta Decay If this process is observed: Neutrino mass ≠ 0 Neutrino = Anti-neutrino! Lepton number is not conserved! Neutrinoless double beta decay lifetime Neutrino effective mass A known standard model process and an important calibration tool Z 0  2  ? 4

5. The neutrino effective mass m ν Decay rate ≈ m ν 2 Effective mass m ν depends on phases: 15 December 2014Paris TPC - 20145

6. Normal Inverted Even a null result will constrain the mass spectrum possibilities! A m  limit of ~20 meV would exclude Majorana neutrinos in an inverted hierarchy.  Sensitivity (mixing parameters from arXiv:1106.6028) 15 December 2014Paris TPC - 2014 50 meV Or ~ 10 27 yr 6

7. Paris TPC - 2014 The traditional search for neutrino-less decay: Measure the energy spectrum of the two electrons… Not yet sufficient to reject backgrounds! 15 December 20147 Energy resolution needed: δE/E < 1% FWHM

8. Historically, there are > 100 experimental limits on T 1/2 of the 0  decay. Here are the records expressed as limits on using one set of nuclear matrix elements (RQRPA of Simkovic et al. 2009.) During the last decade the complexity and cost of experiments has increased very dramatically. The slope constant is now leveling off.  trends (updated Elliott/Vogel plot by Vogel) 15 December 2014Paris TPC - 2014 8 Heidlelberg-Moscow

9. EXO result 15 December 2014Paris TPC - 20149 T  > 1.6 x 10 25 y m  < 140-380 meV 120.7 days 79.4 kg 136 Xe In tension with H-M result, but caveat of matrix elements. EXO result combined with KamLAND -ZEN rules out H-M claim

10. Sensitivity, Background and Exposure 15 December 2014Paris TPC - 201410

11. Various Levels of Confidence in a Result Preponderance of the evidence: – Correct peak energy with no 2-ν contamination – Single-site energy deposit – Proper detector distributions (spatial, temporal) – Rate scales with isotope fraction Beyond a reasonable doubt: – Observe the daughter atom – Observe the two-electron nature of the event – Measure kinematic dist. (energy sharing, opening angle) – Observe the excited state decay Smoking Guns: – See the process consistently in several isotopes – A background-free positive result with enriched isotope – See no peak with depleted isotope – no other changes to detector 11 15 December 2014 Paris TPC - 2014

12. Next Time will be different More than a dozen technical/isotopic approaches have been pursued seriously in the past. The discovery class experiments will be very costly in resources and time, and very few in number. ---------------------------------------------------------------------- How does a “discovery class” experiment differ from a background-limited technique that can only set a limit? Should a background-free requirement be imposed? “Eternity is a very long time, especially towards the end” – Woody Allen 15 December 2014Paris TPC - 201412

13. Next Time will be different More than a dozen technical/isotopic approaches have been pursued seriously in the past. The discovery class experiments will be very costly in resources and time, and very few in number. ---------------------------------------------------------------------- How does a “discovery class” experiment differ from a background-limited technique that can only set a limit? Should a background-free requirement be imposed? “Eternity is a very long time, especially towards the end” – Woody Allen 15 December 2014Paris TPC - 201413

14. Perspective Before embarking on any major new project, the NLDBD community should refocus effort on improvements in technique, to evade the quagmire of background contamination. Where might this focus fall? 15 December 2014Paris TPC - 201414

15. Perspective Before embarking on any major new project, the NLDBD community should refocus effort on improvements in technique, to evade the quagmire of background contamination. Where might this focus fall? Identification of the daughter atom 15 December 2014Paris TPC - 201415

16. Identify the barium daughter by optical spectroscopy (M.Moe PRC44 (1991) 931) Ba + system best studied (Neuhauser, Hohenstatt, Toshek, Dehmelt 1980) Single ions can be detected from a photon rate of 10 7 /s 2 P 1/2 4 D 3/2 2 S 1/2 493nm 650nm metastable 80s 15 December 2014Paris TPC - 201416

17. Identify the barium daughter by optical spectroscopy (M.Moe PRC44 (1991) 931) Ba + system best studied (Neuhauser, Hohenstatt, Toshek, Dehmelt 1980) Single ions can be detected from a photon rate of 10 7 /s Triplet state is quenched in dense gas! Can excite with blue, look only for red Do this in 3-D? Move ion to trap? 2 P 1/2 4 D 3/2 2 S 1/2 493nm 650nm metastable 80s 15 December 2014Paris TPC - 201417

18. Xenon’s daughter: Ba ++ In the DBD decay of 136 Xe, barium daughter will be strongly ionized by the nascent electrons emerging from the nucleus; Partial neutralization occurs by electron capture from neutral xenon atoms ( first ionization potential is 12.14 eV); Process stops at Ba ++ because second ionization potential of Ba ++ is 10.04 eV. It can’t take another electron from neutral xenon. Ba ++ is the expected outcome in pure xenon; For the Ba + spectroscopy to work, one and only one other electron must come from somewhere: charge exchange,…chemistry? 15 December 2014Paris TPC - 201418

19. Might there be another way? Perhaps. Let’s exploit modern biochemistry. My idea: The technique of Single Molecule Fluorescent Imaging may be adaptable here. SMFI: The transformation of a non-fluorescent precursor into a robust and persistent fluorescent state by capture and chelation of doubly ionized alkaline earth elements, such as Ca ++ Maybe Ba ++ too! Ca and Ba are congeners 15 December 2014Paris TPC - 201419

20. Might there be another way? Perhaps. Let’s exploit modern biochemistry. My idea: The technique of Single Molecule Fluorescent Imaging may be adaptable here. SMFI: The transformation of a non-fluorescent precursor into a robust and persistent fluorescent state by capture and chelation of doubly ionized alkaline earth elements, such as Ca ++ Maybe Ba ++ too! Ca and Ba are congeners! 15 December 2014Paris TPC - 201420

21. Conformal changes in Fluo-3 15 December 2014Paris TPC - 201421 Once Ca ++ is captured by Fluo-3, its responsiveness to external excitation increases by a factor of 60 -80. Two-photon excitation with IR is also possible This might work well for Barium too since barium and calcium are congeners. Fluorophores also exist for for Pb ++, Hg ++, Cu… 2014 Nobel Prize in Chemistry awarded to three physicists for developing SMFI

22. Conformal changes in Fluo-3 15 December 2014Paris TPC - 201422 Once Ca ++ is captured by Fluo-3, its responsiveness to external excitation increases by a factor of 60 -80. Two-photon excitation with IR is also possible This might work well for Barium too since barium and calcium are congeners. Fluorophores also exist for for Pb ++, Hg ++, Cu… 2014 Nobel Prize in Chemistry awarded to three physicists for developing SMFI

23. A TPC with biochemistry? One can imagine the TPC cathode surface is coated with untransformed fluorophores waiting to respond strongly after capture of one Ba ++. The Ba ++ ion is now fixed to the cathode surface One can imagine that the cathode surface is a dielectric belt that transports at a few mm/s the latent image to a line imager.ge of the event, and also the needed energy resolution, a la NEXT 15 December 2014Paris TPC - 201423

24. A TPC with biochemistry? One can imagine the TPC cathode surface is coated with untransformed fluorophores waiting to respond strongly after capture of one Ba ++. The Ba ++ ion is now fixed to the cathode surface One can imagine that the cathode surface is a dielectric belt that transports at a few mm/s the latent image to a line imager.ge of the event, and also the needed energy resolution, a la NEXT 15 December 2014Paris TPC - 201424

25. A TPC with biochemistry? One can imagine the TPC cathode surface is coated with untransformed fluorophores waiting to respond strongly after capture of one Ba ++. The Ba ++ ion is now fixed to the cathode surface One can imagine that the cathode surface is a dielectric belt that transports at a few mm/s the latent image to a line imager.ge of the event, and also the needed energy resolution, a la NEXT 15 December 2014Paris TPC - 201425

26. 15 December 2014Paris TPC - 201426

27. Information content Ionization electrons liberated by the decay electrons provide a 3-D image of the event, and the needed energy resolution, a la NEXT This information establishes the domain of possible ion locations to the projected area on the cathode plane. Only the one molecule that has captured the barium ion fluoresces brightly under excitation 15 December 2014Paris TPC - 201427

28. Neutrino Experiment - Xenon TPC Asymmetric TPC with “Separated functions” Paris TPC - 201428 Transparent -HV cathode Energy plane Electroluminescent plane ions Energy & primary scintillation signals recorded here, with PMTs Field cage: teflon EL signal created here Tracking performed here, with “SiPMT” array Virtual Fiducial surface Operating pressure: 10 -15 bars electrons 15 December 2014

29. 29 Topological signature

30. 30 NEXT - DBDM. Energy resolution NEXT-DBDM obtains energy resolution: δE/E = 1.04% FWHM at 667 keV Cs- 137 peak (  0.53% @ Qbb, if not limited by systematics) No tracking. Hard fiducial cut imposed to select only events in the center.

31. 31

32. 32 NEXT Platform and Pb Castle at LSC 65 t of Pb sheets from OPERA disassembled bricks received as a loan (for all the duration of NEXT) by INFN Pb bricks (mainly of standard form) produced by Tecnibusa (5% loss) Three deliveries 7 July 11 August 29 September Cleaning and assembly made by NEXT

33. Perspective The field of NLDBD is entering a new era: “Maybe not big enough to succeed, but too expensive to fail” Failure: a background-dominated result The need for a genuine advance is imperative. Single molecule fluorescent imaging is a novel idea and may open a new pathway to success. – While highly speculative, it serves both as an imagination stretcher and a springboard. 15 December 2014Paris TPC - 201433

34. Summary The discovery of neutrino-less double beta decay would be a major discovery of new physics beyond the Standard Model. – Backgrounds have been present in all sensitive results – Neutrino mass sets sensitivity goal to span inverted hierarchy Discovery class experiments will be very costly ! The need for a genuine advance is imperative. – Single molecule fluorescent imaging of Ba ++ exploiting biochemistry techniques appears possible, and may be practical and efficient A new technique to identify the appearance in space and time of Ba ++ in 136 Xe NLDBD may be a genuine breakthrough! 15 December 2014Paris TPC - 201434

35. Summary The discovery of neutrino-less double beta decay would be a major discovery of new physics beyond the Standard Model. – Backgrounds have been present in all sensitive results – Neutrino mass sets sensitivity goal to span inverted hierarchy Discovery class experiments will be very costly ! The need for a genuine advance is imperative. – Single molecule fluorescent imaging of Ba ++ exploiting biochemistry techniques appears possible, and may be practical and efficient A new technique to identify the appearance in space and time of Ba ++ in 136 Xe NLDBD may be a genuine breakthrough! Thank you for your attention 15 December 2014Paris TPC - 201435

36. Backup slides 15 December 2014Paris TPC - 201436

37. Experimental Parameters W – molecular weight of source f – isotopic abundance x – number of bb isotopes per molecule  – detector efficiency G 0 – decay phase space |M 0 | - matrix element b – background in counts/keV-kg-y  E – energy window in keV M – mass of source in kg T – counting time in years 15 December 2014Paris TPC - 201437 Isotope√(W/(G 0 |M 0 | 2 )) x10 7 Ge2.4(QRPA) 4.7(SM) TeO 2 1.9(QRPA) 3.1(SM) Xe2.4(QRPA) 3.3(SM)

38. 15 December 2014Paris TPC - 201438 The Experimental Challenges Maximize Rate/Minimize Background Large Mass (~ 1 ton) Large Q value, fast  (0 ) Good source radiopurity Demonstrated technology Ease of operation High isotopic abundance Easy enrichment Small volume, source = detector Good energy resolution Slow  (2 ) rate Identify daughter in real time Event reconstruction Nuclear theory b = background/keV ΔE = Energy ROI M = active isotopic mass t live = graduate students

39. Heidelberg-Moscow claim has remained a point of contention ~70 kg-years of data 13 years The “feature” at 2039 keV is arguably present. Data analysis criticized for ex post facto massage NIM A522, 371 (2004) 15 December 201439Paris TPC - 2014

40. Great Number of Proposed Experiments 15 December 201440Paris TPC - 2014 Calorimeter –Semi-conductors –Bolometers –Crystals/nanoparticles immersed in scintillator Tracking –Liquid or gas TPCs –Thin source with wire chamber or scintillator

41. Splitting the window, or in the case of high-event rates, fitting the spectrum. 15 December 2014Paris TPC - 201441 Energy scale for Xe Figure from Mike Moe Fig. from SNO+

42. 42 Energy resolution