 Alpha and gamma have very specific energies  Beta have a continuous distribution of energy  Must be some other particle taking away some of the energy

 Very weakly interacting  “May” be travelling at speed of light  This would imply no rest mass  Measurements done to determine neutrino mass

 2015 Nobel Prize in Physics for Neutrino Oscillations  Two teams: ◦ Japan - Takaaki Kajita ◦ Canada – Art McDonald  Goal is to detect neutrinos ◦ Japanese team used water as target ◦ Canadian team used heavy water

 Causes interference with experiments  Put detector deep underground to shield

 Reverse of beta decay  Neutron absorbs electron neutrino, changes neutron to proton, generates fast electron, detect Cerenkov radiation

 Large tank of Heavy Water, D 2 O  Deuterium in place of hydrogen  Detects neutrinos three ways: ◦ Scatter electron (all neutrinos) ◦ Split deuteron into proton and neutron (all neutrinos) ◦ Inverse beta decay of neutron (electron neutrino only)

 Sun produces only electron neutrinos  Fuses protons into deuterons, release positron and electron neutrino  Detect too few electron neutrinos

 Should see mostly electron neutrinos from Sun  See one third each of electron-, muon- and tau- neutrinos  Means neutrinos change type with time, called Neutrino Oscillations  So…they see the passage of time  Thus, they must have mass  Massless particles travel at the speed of light and do not see the passage of time

Nucleons  Proton 2 U and 1 D  Neutron 2 D and 1 U  Up Q charge +2/3  Down Q charge -1/3

Neutron Proton

 …SNOLAB

 Mass of Up quark 2.3 MeV  Mass of Down quark 4.8 MeV  2 U + 1 D = 9.4 MeV  Mass of Proton = 938 MeV  Only 10% of the Proton mass is quarks?