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Future Zero-Neutrino Double Beta Decay Experiments

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Future Zero-Neutrino Double Beta Decay Experiments
Outline Neutrino Mass and bb General Experimental Issues The Matrix Elements The New Proposals Steve Elliott, UK Forum 2003

Neutrino Mass: What do we want to know?
Relative Mass Scale Absolute Mass Scale Dirac or Majorana ne n1 n2 n3 Mixing Steve Elliott, UK Forum 2003

3 Complementary Experimental Techniques
Need all three types of experiments to fully understand the nature of the n. Steve Elliott, UK Forum 2003

Neutrino Masses <mb> < 2.2 eV Sets mn scale > 50 meV
Direct mass and bb experiments set absolute mass scale. <mb> < 2.2 eV The results of oscillation experiments set the relative mass scale. Sets mn scale > 50 meV bb addresses Dirac/Majorana nature of n. Steve Elliott, UK Forum 2003

Example Decay Scheme In many even-even nuclei, b decay is
Endpoint Energy In many even-even nuclei, b decay is energetically forbidden. This leaves bb as the allowed decay mode. Steve Elliott, UK Forum 2003

bb(2n): Allowed and observed 2nd order weak process.
bb(2n) vs. bb(0n) bb(2n): Allowed and observed 2nd order weak process. bb(0n): requires massive Majorana neutrinos even in presence of alternative mechanisms. Steve Elliott, UK Forum 2003

Energy Spectrum for the 2 e-
Endpoint Energy Steve Elliott, UK Forum 2003

bb Decay Rates G are calculable phase space factors. G0n ~ Q5
|M| are nuclear physics matrix elements. Hard to calculate. mn is where the interesting physics lies. Steve Elliott, UK Forum 2003

What about mixing, mn & bb(0n)?
No mixing: virtual n exchange e = ±1, CP cons. Mbb is a coherent sum because the neutrino is virtual. Mv is an incoherent sum because the neutrinos are real. Compare to b decay result: real n emission Steve Elliott, UK Forum 2003

From KamLAND, solar n and atmospheric n
Neutrino Mixing From KamLAND, solar n and atmospheric n Steve Elliott, UK Forum 2003

Min. <mbb> as a vector sum
<mbb> is the modulus of the resultant vector in the complex plane. (In this example, <mbb> has a min. It cannot be 0.) min Figure from: PR D63, Steve Elliott, UK Forum 2003

More General: 3 n (Inverted Heir.)
<mbb> 30 meV or few x 1027 yr Plot Thanks to Petr Vogel msmallest Steve Elliott, UK Forum 2003

More General: (Normal Heir.)
30 meV or few x 1027 yr Plot Thanks to Petr Vogel Steve Elliott, UK Forum 2003

Physics Reach Solar + KamLAND + Atmospheric (Ue3~ 0) Normal Hierarchy
Inverted Hierarchy Degenerate m1 ~ 0 meV ~55 meV = M > about 100 meV m2 ~ 7 meV M m3 ~ 55 meV ~0 meV <mbb> ~ 5 meV 28 or 55 meV M/2 or M Solar + KamLAND + Atmospheric (Ue3~ 0) Steve Elliott, UK Forum 2003

For the next experiments:
An exciting time for bb! For at least one neutrino: For the next experiments: < mbb > in the range of 10 - 50 meV is very interesting. Steve Elliott, UK Forum 2003

<mbb> History 1948 Earliest measurements by Fireman used Geiger counter tube coincidence to look for 2 electrons.. Early 50ies, Cloud chamber experiments were an improvement Mid fifties, the big step forward was the meausruement of the sum energy of the 2 electrons and looking for a peak. ~2015 |M| Reference Eur. Lett. 13, 31 (1990) Steve Elliott, UK Forum 2003

An Ideal Experiment Maximize Rate/Minimize Background
Large Mass (~ 1 ton) Good source radiopurity Demonstrated technology Natural isotope Small volume, source = detector Good energy resolution Ease of operation Large Q value, fast bb(0n) Slow bb(2n) rate Identify daughter Event reconstruction Nuclear theory Steve Elliott, UK Forum 2003

Classes of Background bb(2n) tail
Need good energy resolution. Natural U, Th in source and shielding Pure materials, identify bb daughter, pulse shape, timing, position. Cosmic ray activation Store and prepare materials underground. Steve Elliott, UK Forum 2003

bb(2n) as a Background. Sum Energy Cut Only
next generation experimental goal Steve Elliott, UK Forum 2003

Target: t(bb(0n) ~ 1027 years Cryostat, or other experimental support
Natural Activity The Problem: t(U, Th) ~ 1010 years Target: t(bb(0n) ~ 1027 years Detector Shielding Cryostat, or other experimental support Front End Electronics etc. Steve Elliott, UK Forum 2003

Cosmic Ray Induced Activity
Material dependent. Need for depth to avoid activation. Need for storage to allow activation to decay. Steve Elliott, UK Forum 2003

Evidence of 68Ge From: NIM A292 (1990) Experimental data from two 1.05 kg natural detectors Integral of this spectrum equals integral of this peak. ROI This peak decays with the right half life. Steve Elliott, UK Forum 2003

Depth Requirement Remove Surface Activation
100 mwe, low E neutrons from rock Muons ~30% of events in ROI vetoed at 2500 mwe Muon-induced secondary activation Still observed at low E at 2000 mwe. For MOON-like natMo expt., ~ Mo(n,2n)91Mo per year m directly induced OK at 4700 mwe (e.g. SAGE) Unknown components Deeper is better! Steve Elliott, UK Forum 2003

There are many calculations.
Matrix Elements There are many calculations. Most authors quote mass limits derived from all or at least representatives of the whole range. How do we interpret the uncertainty associated with the mass due to the nuclear physics? Steve Elliott, UK Forum 2003

<mbb> Uncertainties
Imagine signal at 7x1026 years 500 kg for 10 years ~50% unc. for t1/2 (with BG) ~20% without BG |M| Range: meV Statistics (with BG): ±25 meV Steve Elliott, UK Forum 2003

Statistical contribution contribution to uncertainty.
Consider a 100 meV result. Statistical contribution to uncertainty. Our conclusion about the possible range of m1 would be greatly affected by this uncertainty. In fact if coupled with a fortuitous beta decay measurement the possibility to exclude the inverse hierarchy could be lost. Matrix Element contribution to uncertainty. Would this exclude the inverted hierarchy with small msmallest? Need improvement in the Theory. Steve Elliott, UK Forum 2003

“Found” Peaks Need more than one experiment A 2527-keV Ge-det.
PR D45, 2548 (1992) A 2527-keV Ge-det. peak that was an electronic artifact. NP B35 (Proc. Supp.), 366 (1994). A ~2528-keV Te-det. peak that was a 2s Statisticalflucuation. Steve Elliott, UK Forum 2003

A Great Number of Proposed Experiments
COBRA Te-130 10 kg CdTe semiconductors DCBA Nd-150 20 kg Nd layers between tracking chambers NEMO Mo-100, Various 10 kg of bb isotopes (7 kg of Mo) CAMEO Cd-114 1 t CdWO4 crystals CANDLES Ca-48 Several tons CaF2 crystals in liquid scint. CUORE 750 kg TeO2 bolometers EXO Xe-136 1 ton Xe TPC (gas or liquid) GEM Ge-76 1 ton Ge diodes in liquid nitrogen GENIUS GSO Gd-160 2 t Gd2SiO5:Ce crystal scint. in liquid scint. Majorana 500 kg Ge diodes MOON Mo-100 Mo sheets between plastic scint., or liq. scint. Xe 1.56 t of Xe in liq. Scint. XMASS 10 t of liquid Xe Steve Elliott, UK Forum 2003

Potential Large-Mass (~1 ton) Future Experiments
Experiments in Europe CUORE, GENIUS NUSEL Candidates EXO*, MAJORANA, MOON Smaller Mass and Development Experiments Cobra*, DCBA, NEMO*, CAMEO, CANDLES, GSO… Steve Elliott, UK Forum 2003

The MOON Collaboration:
H.Ejiri, Y. Itahashi, N. Kudomi, M. Nomachi, T. Shima RCNP, Osaka Univ. Japan R. Hazama, K. Matsuoka, Y. Sugaya, S. Yoshida Phys. Dept. Osaka Univ. Japan K. Fushimi, K. Ichihara, Y. Shichijo University of Tokushima, Japan P.J. Doe, V. Gehman, R.G.H. Robertson, O. E. Vilches, J.F. Wilkerson, D.I. Will CENPA, Univ. Washington Seattle, USA S.R. Elliott, LANL, USA J. Engel Univ. North Carolina, USA A. Para, FNAL, USA M. Greenfield, International Christian Univ., USA M. Finger Phys. Dept., Charles Univ., Prague, Czech Republic A. Gorin, I.Manouilov, A. Rjazantsev Inst. High Energy Physics, Protvino, Russia K. Kuroda, P. Kavitov, V. Vatulin, VNIIEF, Sarov, Russia V. Kekelidze, V. Kutsalo, G. Shirkov, A. Sisakian, A. Titov, V. Voronov, JINR, Dubna, Russia In Association with: The Majorana Collaboration C. Aalseth, F. Avignone, S.R. Elliott, H. Miley…... Steve Elliott, UK Forum 2003

MOON is 4 experiments… 100Mo  100Tc 100Mo CC Solar n 100Ru 100Ru ?
0.168  100Tc 100Mo 16 s 1.00 x 1019 y -3.034 CC Solar n 100Ru -3.034 100Ru ? 100Mo -1.293  H. Ejiri et al. PRL 85 (2000) 2917 6.1 x 1020 y -1.904 100Ru Hamish Robertson APS, April 5, 2003 Steve Elliott, UK Forum 2003

Signal Rates per year per ton of 100Mo
0nbb (ground state) 20 (<m> / 50 meV)2 2nbb (ground state) 3.6 x 108 0nbb (0+1 state) .03 (<m> / 50 meV)2 2nbb (0+1 state) 0nbb (0+2 state) 6.9 x 106 .5 (<m> / 50 meV)2 pp 120 7Be 40 pep 2.5 8B 5.1 13N 4.2 15O 6.1 * * * SSM rates *QRPA: J. Souhonen, NP A700, 649 (2002). 76Ge : 3.8 (<m> / 50 meV)2 Steve Elliott, UK Forum 2003

MOON Overview 3.3 tons 100Mo, 34 tons Mo
Doesn’t require enriched material (but would probably want it). Scintillator/source sandwich Position and single Eb data play big role in bb(2n) and U, Th rejection. Or possibly bolometer 14% efficiency ELEGANTS is precursor. Steve Elliott, UK Forum 2003

Detection Techniques under Consideration:
Scintillator Mo Foil Sandwich Mo loaded liquid scintillator Cryogenic calorimeter One possible configuration scintillator Readout fibers Mo foil 1 module: Mo foil, 6m x 6m x 0.05 gm/cm Scintillator 6m x 6m x 0.25cm 222 wavelength shifting fibers Super module (detector) 1950 Modules 6m x 6m x 5m 34 t nMo (3 t 100Mo) 13600, 16-anode PMT readout Steve Elliott, UK Forum 2003

MOON Prototype Steve Elliott, UK Forum 2003

Cryogenic Underground Observatory for Rare Events - CUORE
Berkeley Firenze Gran Sasso Insubria (COMO) Leiden Milano Neuchatel U. of South Carolina Zaragoza Spokesperson Ettore Fiorini Milano Steve Elliott, UK Forum 2003

CUORE Overview 0.21 ton, 34% natural abundance 130Te
TeO2 bolometers, 750 g crystals Doesn’t require enriched material. 1020 5x5x5 cm3 crystals 25 towers of 10 layers of 4 crystals Gran Sasso Laboratory CUORICINO is an approved prototype (1 tower). CUORICINO began operation in Feb. 2003 Steve Elliott, UK Forum 2003

CUORE Detector Detector Damping Suspension Dilution Unit Thermal
Shields Steve Elliott, UK Forum 2003

CUORICINO IS OPERATING
FIRST PULSE. Data runs began In Feb. 2003 Steve Elliott, UK Forum 2003

Enriched Xenon Observatory - EXO
U. of Alabama Caltech IBM Almaden ITEP Moscow U. of Neuchatel INFN Padova SLAC Stanford U. U. of Torino U. of Trieste WIPP Carlsbad Spokesperson Giorgio Gratta Stanford Steve Elliott, UK Forum 2003

EXO Overview (latter talk)
10 ton, ~70% enriched 136Xe 70% effic., ~10 atm gas TPC or LXe chamber Optical identification of Ba ion. Drift ion in gas to laser path or extract on cold probe to trap. TPC performance similar to that at Gottard. 100-kg enrXe prototype (no Ba ID) Isotope in hand Steve Elliott, UK Forum 2003

The Majorana Project Co-Spokespersons Frank Avignone Harry Miley
Duke U. North Carolina State U. TUNL Argonne Nat. Lab. JINR, Dubna ITEP, Moscow New Mexico State U. Pacific Northwest Nat. Lab. U. of Washington LANL LLNL U. of South Carolina Brown Univ. of Chicago RCNP, Osaka Univ. Univ. of Tenn. Co-Spokespersons Frank Avignone Harry Miley Steve Elliott, UK Forum 2003

Majorana Overview 0.5 ton of 86% enriched 76Ge
Segmented detectors using pulse shape discrimination to improve background rejection. Prototype ready to go this fall/winter. (14 crystals, 1 enriched) 100% efficient Can do excited state decay. IGEX is precursor Steve Elliott, UK Forum 2003

Majorana Layout Steve Elliott, UK Forum 2003

AGe + fast n -> 68Ge + X 68Ge 68Ga 68Zn
288d 68Ge 68Ga 68Zn 2.9 MeV 68Ge is the dominate background. For 500-kg enriched detector, initially expect ~500 68Ge decays/day. t1\2 = 288 d The naturally occurring 40K in the human body decays at a rate of decays/second. Steve Elliott, UK Forum 2003

Why Segmentation and Pulse Shape Analysis?
bb is pointlike. b+ or Compton scattered g rays deposit energy in multiple locations. Segmentation and PSD help reduce these Backgrounds. Steve Elliott, UK Forum 2003

Recent Crystal Packaging Test (MEGA)
Steve Elliott, UK Forum 2003

GErmanium NItrogen Underground Setup - GENIUS
MPI, Heidelberg Kurchatov Inst., Moscow Inst. Of Radiophysical Research, Nishnij Novgorod Braunschweig und Technische Universität, Braunschweig U. of L'Aquila, Italy Int. Center for Theor. Physics, Trieste JINR, Dubna Northeastern U., Boston U. of Maryland, USA University of Valencia, Spain Texas A & M U. Spokesperson Hans Klapdor-Kleingrothaus MPI GENIUS Steve Elliott, UK Forum 2003

GENIUS Overview 1 ton, ~86% enriched 76Ge Naked Ge crystals in LN
Very little material near Ge. 1.4x106 liters LN 40 kg test facility is approved. 100% efficient Heid.-Moscow experiment is precursor GENIUS Steve Elliott, UK Forum 2003

GENIUS Layout Clean Room Data Acquisition Insulation Liquid Nitrogen Setup for operation of three 'naked’ Germanium detectors in liquid nitrogen. Steel Vessel 12 m GENIUS Steve Elliott, UK Forum 2003

A Recent Claim for bb(0n)
Mod. Phys. Lett. A16, 2409 (2001) Steve Elliott, UK Forum 2003

The Controversy. Locations of claimed peaks Mod. Phys. Lett. A16, 2409 (2001) If one had to summarize the controversy in a short statement: Consider two extreme background models: 1. Entirely flat in keV region. 2. Many peaks in larger region, only bb peak in small region. These 2 extremes give very different significances for peak at 2039 keV. KDHK chose Model 2 but did not consider a systematic uncertainty associated with that choice. Steve Elliott, UK Forum 2003

Summary of Proposals The <mbb> limits depend on background assumptions and matrix elements which vary from proposal to proposal. Steve Elliott, UK Forum 2003

UG Lab space will be needed for some of that R&D.
Conclusions Research and Development are needed for all the future proposed detectors. UG Lab space will be needed for some of that R&D. The next generation bb experiments have a good possibility of reaching an interesting <mbb> region. Steve Elliott, UK Forum 2003

Pulse Shape Discrimination
Steve Elliott, UK Forum 2003

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