How Can Neutrinoless Double Beta Decay Tell Us Anything About Neutrinos??

How can Neutrinoless Double Beta Decay tell us anything about Neutrinos??

• The Standard Model has only left-handed neutrinos. Must be massless. • Experiment (oscillations) show neutrinos have mass. We can bring them to rest! • Therefore there must be a right-handed neutrino. Dirac • What is that object? Is it a sterile particle with no interactions, or is it an antineutrino? Majorana

Hamish Robertson, INT Workshop June 23, 2005 How can we find the answer?

• One might suppose trying an experiment to see if neutrinos induce the same reactions as antineutrinos; e.g. Ray Davis showed that 37 37 $ " e + Cl# Ar + e did not proceed. This, however, is an inevitable consequence of the left-handedness of the weak interaction, and does not show

! " e # " e

! Example ββ Decay Scheme

In many even-even 76 As nuclei, β decay is energetically 0+

forbidden. This 76 leaves ββ Ge as the allowed 0+ decay mode. !! 2+ Endpoint Energy 0+

76 Se

S.R. Elliott A Great Number of Proposed Experiments Many international collaborations

48 CARVEL Ca-48 100 kg CaWO4 crystal scintillators COBRA Cd-116, Te-130 10 kg CdTe semiconductors DCBA Nd-150 20 kg Nd layers between tracking chambers NEMO Mo-100, Various 10 kg of ββ isotopes (7 kg of Mo), expand to superNEMO

CAMEO Cd-116 1 t CdWO4 crystals

CANDLES Ca-48 Several tons CaF2 crystals in liquid scint.

CUORE Te-130 750 kg TeO2 bolometers EXO Xe-136 1 ton Xe TPC (gas or liquid) GEM Ge-76 1 ton Ge diodes in liquid nitrogen GENIUS Ge-76 1 ton Ge diodes in liquid nitrogen GERDA Ge-76 ~30-40 kg Ge diodes in LN, expand to larger masses

GSO Gd-160 2 t Gd2SiO5:Ce crystal scint. in liquid scint. Majorana Ge-76 ~180 kg Ge diodes, expand to larger masses MOON Mo-100 Mo sheets between plastic scint., or liq. scint. Xe Xe-136 1.56 t of Xe in liq. Scint. XMASS Xe-136 10 t of liquid Xe

S.R. Elliott A Great Number of Proposed Experiments Many international collaborations

48 CARVEL Ca-48 100 kg CaWO4 crystal scintillators COBRA Cd-116, Te-130 10 kg CdTe semiconductors DCBA Nd-150 20 kg Nd layers between tracking chambers NEMO Mo-100, Se-82 10 kg of ββ isotopes (7 kg of Mo), expand to superNEMO

CAMEO Cd-116 1 t CdWO4 crystals

CANDLES Ca-48 Several tons CaF2 crystals in liquid scint.

e- νe Z

Z + 1 νe e- Z+2 # 2n " 2 p + 2e + 2$ e

S.R. Elliott

! ββ(0ν): requires massive Majorana ν Only practical way to address the particle-antiparticle question e-

Z νe e-

Z +1

" n ! p + e + #e Z+2 (RH " ) e (LH "e ) # !e + n " p + e

S.R. Elliott !

! Energy and Angular Correlations in 0νββ Decay ββ Decay Rates

2 2 2 !2 " = G2" M2 " !0 " = G0" M0 " m"

G are calculable phase space factors. 5 G0ν ~ Q |M| are nuclear physics matrix elements. Hard to calculate. mν is where the interesting physics lies.

S.R. Elliott Key Point:

• No matter what mechanism leads to neutrinoless ββ decay (Majorana mass, Right-handed currents, R- parity violating SUSY particle exchange), it means neutrinos are Majorana particles.

• That follows from the non-conservation of lepton number. What about mixing, mν & ββ(0ν)?

No mixing: m!! = m"e = m1

3 2 m!! = " Uei mi #i with mixing: i=1 ε = ±1, CP cons.

S.R. Elliott Matrix Elements: gpp adjusted to 2νββ

V. Rodin et al. nucl-th/0503063 (Rodin et al. 05)

9.2 / t y for

= 100 meV (Rodin et al.) (Simkovic et al. 04)

9.2 / t y for

= 100 meV (Rodin et al.) (NuSAG’s Choice)

5.9 / t y for

= 100 meV (Rodin et al.) Signal Rates per year per ton of 100Mo

0νββ (ground state) 3 ( / 50 meV)2 ν † 2νββ (ground state) 3.6 x 108 0νββ (0+ state) .03 ( / 50 meV)2 1 ν * + 6 2νββ (0 1 state) 6.9 x 10 0νββ (0+ state) .5 ( / 50 meV)2 2 ν * pp 120 SSM 7Be 40 rates pep 2.5 8B 5.1 13N 4.2 15O 6.1

† QRPA/RQRPA: Rodin et al. nucl-th/0503063 [76Ge : 2.3 2 ( / 50 meV) per year per ton] *QRPA: J. Souhonen, NP A700, 649 (2002). Signal and Background vs Depth R&D: Enriched 100Mo

• VNIIEF is ready to produce 1 kg immediately, and 0.1 t / y soon.

• Centrifugal separation of MoF6 gas • Rate 0.5 t 100Mo (90 %) / 5 y with 6000 centrifuges and 40 processes.

120 0.16

0.14 100 Production rate of ??100 0.12 (g/day) 80 0.1 separator

60 0.08 one of rate izotope output (%) 0.06 40

0.04 production

20 0.02

0 0 10 20 30 40 50 60 70 80 90 100 110 120 number of stages (separators) APS Multidivisional Study (http://www.aps.org/neutrino/)

The APS neutrino study on the future US Neutrino Program made a few things clear. • One of the three principal conclusions: “WE RECOMMEND, AS A HIGH PRIORITY, A PHASED PROGRAM OF SENSITIVE SEARCHES FOR NEUTRINOLESS NUCLEAR DOUBLE BETA DECAY.” • It further recommends a staged approach beginning with 100-200 kg scaling later to 1 ton. – Precision measurement at degenerate scale – Followed by discovery potential at atmospheric scale • It emphasized the need for multiple experiments using different isotopes NSAC Subcommittee

• Nuclear physics has produced dramatic advances in neutrino science, with the demonstration of flavor change, mass, and oscillations. These discoveries open enormous opportunities in neutrino science, which represents a major priority for nuclear physics. • A multipurpose deep underground laboratory, an NSF initiative, remains a high priority for nuclear physics research in the areas of neutrino physics and nuclear astrophysics.

For all succeeding budget scenarios, the subcommittee recommends that funds remain in the program to: initiate new experiments in neutrino science and fundamental symmetries; increase support for nuclear theory; carry out upgrades at the two low-energy user facilities, ATLAS and HRIBF; and continue R&D for RIA.

Tail of 2ν competes with 0ν 10-6 ratio shown: 100Mo is 10-8

5% FWHM

Elliott and Vogel, ARNPS 2002