Is the Neutrino its Own Antiparticle?

Is the Neutrino its Own Antiparticle? PHYS 294A Jan 24, 2013

Outline What s a neutrino? The case for Majorana neutrinos Probing the nature of the neutrino with neutrinoless double-beta decay 2

What s a Neutrino? Meitner and Hahn (1911): 2 Bi 3

What s a Neutrino? Meitner and Hahn (1911): 2 Po e - 4

What s a Neutrino?? Meitner and Hahn (1911): 2 Po e - 5

What s a Neutrino? Wolfgang Pauli (1931): ν q = 0 spin = ½ m m p color = 0 2 Po e - 6

What s a Neutrino? Enrico Fermi (1934): Little neutral one ν Possible interactions: EM Strong Weak Gravity 2 Po e - 7

Neutrinos and Antineutrinos n ν H e - e + H D ν 37 Ar H e + 37 Cl e - 8

Neutrinos and Antineutrinos Nuclear Reactor Scintillator (CxHy) ν PMTs The Sun Cleaning fluid (Cl) ν + Ar detector 9

Neutrinos and Antineutrinos Nuclear Reactor Scintillator (CxHy) ν Cowan and Reines (1956) PMTs The Sun Cleaning fluid (Cl) ν Ray Davis Jr. (1964) + Ar detector

Neutrinos and Antineutrinos Nuclear Reactor Scintillator (CxHy) νr Cowan and Reines (1956) PMTs The Sun Cleaning fluid (Cl) νl Ray Davis Jr. (1964) + Ar detector 11

Neutrino Handedness neutrinos: left-handed Direction of motion Direction of spin antineutrinos: right-handed 12

Standard Model Particles 13 Credit: Fermilab

Standard Model Particles m = 0, left-handed only 14 Credit: Fermilab

Outline What s a neutrino? The case for Majorana neutrinos Probing the nature of the neutrino with neutrinoless double-beta decay 15

Neutrino Oscillation νe partially νx νe http://www.sciencephoto.com/media/342241/enlarge 16 KamLAND Collaboration, Phys. Rev. D 83, 052002 (2011).

Neutrino Oscillation νe = Ue1ν1 + Ue2ν2 + δν3 νe partially νx νe http://www.sciencephoto.com/media/342241/enlarge m2 2 - m1 2 17 KamLAND Collaboration, Phys. Rev. D 83, 052002 (2011).

Incorporating ν Mass 18 H. Murayama, Physics World (May 2002).

Incorporating ν Mass md md 19 H. Murayama, Physics World (May 2002).

Incorporating ν Mass md Not in SM md 20 H. Murayama, Physics World (May 2002).

Incorporating ν Mass md Not in SM md 21 H. Murayama, Physics World (May 2002).

The Majorana Equation Schrodinger: 22

The Majorana Equation Schrodinger: Dirac: 23

The Majorana Equation Schrodinger: Dirac: Majorana: 24 E. Majorana, Il Nuovo Cimento 14, 171 (1937). English translation: Soryushiron Kenkyu 63, 149 (1981).

Dirac vs Majorana neutrinos Dirac (ν ν) Majorana (ν = ν) νl produces - ( ) νl produces - νr doesn t interact ( ) νr produces + νl doesn t interact Requires Q = -Q = 0 Implies L is violated νr produces + 25 Following B. Kayser.

Seesaw Mechanism mass M, τ ~ 1/M md NR md 26 H. Murayama, Physics World (May 2002).

Seesaw Mechanism mass M, τ ~ 1/M md NR md M md md 27 H. Murayama, Physics World (May 2002).

Seesaw Mechanism mass M, τ ~ 1/M md NR md M md md Majorana mass term mν ~ md 2 /M 28 H. Murayama, Physics World (May 2002).

Seesaw Mechanism mass M, τ ~ 1/M md NR md M md md Majorana mass term mν ~ md 2 /M M md mν for md ~ GeV-TeV: mν ~ mev-ev M ~ 16-19 GeV 29 H. Murayama, Physics World (May 2002).

Grand Unification 30 GUT scale Plank scale = ħc/g

Matter-Antimatter Asymmetry The Big Bang The Universe Today matter + antimatter matter only 31

Sakharov Conditions Interactions out of thermal equilibrium Baryon number violation (baryogenesis) C (charge) and CP (charge-parity) violation 32 A. Sakharov, JETP 5, 24 (1967).

Leptogenesis Decay of heavy Majorana neutrino (N) into SM leptons ( ± ) and Higgs (H): - + N N H H CP violation in ν sector could give these different branching ratios SM processes could convert L to B: baryogenesis! Majorana neutrinos could be the reason we exist at all! 33 Following B. Kayser.

Outline What s a neutrino? The case for Majorana neutrinos Probing the nature of the neutrino with neutrinoless double-beta decay 34

Double-Beta Decay M Z 35

Double-Beta Decay 2νββ e - e - νe νe W - W - > Nuclear Process > (A, Z) (A, Z+2) 36

0νββ Decay 2νββ e - e - νe νe W - W - > Nuclear Process > (A, Z) (A, Z+2) 0νββ e - e - Uei νi mi x W - W - Uei > Nuclear Process > (A, Z) (A, Z+2) Γ½ 0ν = G 0ν M 0ν 2 mββ 2 mββ Σ mi Uei 2 37

0νββ Decay 3 2 [mev] ββ m Inverted Normal Normal Inverted 1-1 1 m lightest [mev] 2 3 A. Schubert, H. Murayama Osc. pars. from Fogli et al., arxiv:1205.5254v2.

Claimed Observation Klapdor Kleingrothaus et al., Mod. Phys. Lett. A 21 (2006) p 1547. 71.7 kg y T1/2 = (2.23 +0.44 0.31) x 25 y significance ~6σ mββ < ~150-600 mev

Claimed Observation 40 Klapdor Kleingrothaus et al., Phys. Lett. B 586, 198 (2004).

3 Double-Beta Decay Claimed signal in 76 Ge: Mod. Phys. Lett. A 21 (2006) p 1547. 2 [mev] ββ m 1 Inverted Normal -1 1 m lightest [mev] 2 3

3 Double-Beta Decay Disfavored by 0νββ Claimed signal in 76 Ge: Mod. Phys. Lett. A 21 (2006) p 1547. 2 [mev] ββ m 1 Inverted Normal -1 1 m lightest [mev] 2 3

3 Double-Beta Decay Disfavored by 0νββ Claimed signal in 76 Ge: Mod. Phys. Lett. A 21 (2006) p 1547. 2 [mev] ββ m 1-1 Inverted Normal 1 m lightest [mev] 2 Disfavored by cosmology; To be tested by KATRIN 3

3 Double-Beta Decay Disfavored by 0νββ Claimed signal in 76 Ge: Mod. Phys. Lett. A 21 (2006) p 1547. 2 [mev] ββ m 1-1 Inverted Normal 1 m lightest [mev] 2 Disfavored by cosmology; To be tested by KATRIN 3

3 Double-Beta Decay Disfavored by 0νββ Claimed signal in 76 Ge: Mod. Phys. Lett. A 21 (2006) p 1547. 2 [mev] ββ m 1-1 Inverted Normal 1 m lightest [mev] 2 Disfavored by cosmology; To be tested by KATRIN 3

Testing the Inverted Hierarchy sensitivity (90% CL, QRPA NME) [mev] ββ m 3 2 Mod. Phys. Lett. A 21 (2006), p. 1547 (3σ): (1.30-3.55) x Inverted Hierarchy (m l 0 ev) Zero background 0.1 counts/roi/t/y 1 count/roi/t/y 4 counts/roi/t/y 25 years 25 26 27 28 76 0ν Ge T 1/2 sensitivity (90% CL) [years] -3-2 -1 1 Exposure [tonne years]

0νββ Experiments Construction Operation 47 Elliott, arxiv:1203.70v1 (2012).

0νββ Experiments UW involvement Construction Operation 48 Elliott, arxiv:1203.70v1 (2012).

The MAJORANA DEMONSTRATOR (MJD) 40 kg of Ge detectors, 30 kg enriched. Located at the 4850 level of Sanford Underground Laboratory in SD Modules: Goal: x0 reduction in background using clean materials, hit patterns, pulse-shapes Prototype: 2 strings natge (under construction!) Module 1: 4xnatGe + 3xenrGe (2013) Module 2: up to 7 strings enrge (2014) 49

Summary Neutrinos continue to give us new mysteries to solve Majorana neutrinos may give us insights into Grand Unification and the Matter- Antimatter Asymmetry of the Universe 0νββ experiments are the only known way to probe this aspect of the neutrino. Definitive tests of inverted hierarchy Majorana neutrinos are within reach! 50

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Neutrino Handedness e - C.S. Wu et al. (1957) Co 60 νe 52

The Majorana Fermion Particle physics: Δ Condensed matter: charge-neutral, zero-energy quasi-particle 53 Brouwer, Science 336, 989 (2012).

Testing ν = ν (I) Dirac ν Majorana ν νl produces - ( ) νl produces - νr doesn t interact ( ) νr produces + νl doesn t interact Why not generate νr in a beam and see if it νr produces + produces +? 54 Following B. Kayser.

Testing ν = ν (I) νl π + π + μ + νr μ + π + at rest boost High-E π + beam Boost so that π + beam faster than νl from decay at rest: requires Eπ > 4 PeV (n.b. LHC = 14 TeV) Fraction of decays with helicity flipped: <-15 Since L-violation comes only from Majorana ν masses, any attempt to observe it will be at the mercy of the ν masses. - B. Kayser 55 Following B. Kayser.

Germanium Detectors ~7 cm ~7 cm 56

Point-Contact Ge Detectors Hole vdrift (mm/ns) w/ paths, isochrones 57

Point-Contact Ge Detectors γ + + _ + ++ + + + Edep Hole vdrift (mm/ns) w/ paths, isochrones 58

Point-Contact Ge Detectors ~x 59 Barbeau et al., JCAP 09, 009 (2007).