How do you weigh a neutrino?

1. How do you weigh a neutrino? And why would one want to do that! Recent underground experiments have demonstrated that n’s must have mass! • Atmospheric neutrinos: SuperKamiokande (1998) • Solar neutrinos: Chlorine (1970s) --> SNO (2001, 2002) • Reactor antineutrinos: KamLAND (2002) These results tell us neutrinos have mass, but don’t tell us what the mass is. These results also disagree with physicists’ long held “standard” model In the standard model - massless neutrinos were frankly a bit dull, perhaps even boring John Wilkerson

2. n’s with mass: exciting “superhero” particles As n’s travel through space or matter they transform from one type (flavor)of neutrino to another? Neutrinos play important roles in • how stars burn • how stars die (supernovae explosions) • the creation of the heavier elements There are lots of neutrinos in the universe (~330 / cm3). So even with a small mass, they collectively are equal to the mass of all the stars and luminous gases in the universe! Thus they can influence the evolution of the early universe They could potentially be the reason for the observed matter - antimatter asymmetry. (We don’t know yet!) Neutrinos may even be their own anti-particle! (don’t know yet!) John Wilkerson

3. n physics - more questions than answers! Since the current model is wrong, what is the correct model? Mass opens up an array of interesting theoretical possibilities. What is the nature of these “massive” neutrinos? • What is the relationship between the neutrino “flavors” we observe in nature and the neutrino “mass” states. • Is there a connectionbetween neutrinos and other fundamental particles (quarks) and the origin of mass? • What symmetry laws do neutrinos obey? Might neutrinos be their own anti-particle? • What are the neutrino masses? John Wilkerson

4. e- Beta decay: Nucleus (A, Z) Nucleus (A, Z+1)+e-+ne n p +e-+ne Z+1 ne Z 2 n Double Beta decay: Nucleus (A, Z) Nucleus (A, Z+2)+e-+ne+e-+ne 76Ge 76Se+e-+ne +e-+ne e- Z+2 e- ne Z ne e- Z+2 e- ne Z ne How do you weigh a neutrino? NeutrinolessDouble Beta decay Neutrinoless Double Beta decay: Nucleus (A, Z) Nucleus (A, Z+2)+e-+e- 76Ge 76Se+e-+e- John Wilkerson

5. NeutrinolessDouble Beta decay • If neutrinos are their own anti-particles, a nucleus that decays via double beta decay will do so at a rate proportional to effective neutrino mass. • (The slower the decay, the longer lifetime for the nucleus.) • Crucial Challenge - measuring extremely rare decay rates: • Best experiments to date (10 kg) T1/2 > 2  1025 years (~.3 eV) • Requirements for next generation experiments: • Sufficient mass, ~ 500 - 1000 kg (a factor of 100 increase!) • Extremely low backgrounds • deep underground, ultra clean materials • Good detector energy resolution • Goal: T1/2 ~ 1026 - 1027 years John Wilkerson

6. Next generation 0 n bb-decay experiments Majorana CUORE EXO MOON John Wilkerson

7. Majorana Collaboration Proposed Detector • Requires: • 500 kg enriched 85% 76Ge • many crystals, each segmented • advanced signal processing • Pulse shape discrimination • special low bkg materials • deep underground location • Sensitive to effective Majorana n mass as low as 0.02-0.07 eV • 0nbb decay of 76Ge potentially measured at 2039 keV • Based on well known 76Ge detector technology plus: • Pulse-shape analysis • Detector segmentation • Ready to begin now John Wilkerson