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?