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Lepton physics & weak interactions

Lepton physics & weak interactions. The neutrino hypothesis. Given that you can only measure. What physics observations/measurements prompted the addition of the neutrino?. How was the neutrino hypothesis confirmed?. Fission reactor. Liquid scintillator. Shielding. Electronics.

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Lepton physics & weak interactions

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  1. Lepton physics &weak interactions

  2. The neutrino hypothesis Given that you can only measure What physics observations/measurements prompted the addition of the neutrino? How was the neutrino hypothesis confirmed?

  3. Fission reactor Liquid scintillator Shielding Electronics Many PMTs The neutrino hypothesis

  4. Neutrino source(Fission reactor)neutron rich nuclides Hydrocarbon scintillator “target” E = 9.1 MeV (b) (a) Light - PMTs Coincidence expt(a) [10s]  (b) Reines & Cowan (Nobel Prize) The neutrino hypothesis

  5. The neutrino hypothesis

  6. The two neutrino hypothesis

  7. Left-handed particles Right-handed particles Neutrino helicity (Not arbitrary assignments!

  8. Eu-152 0  1 Sm-152*  E1 Sm-152 0 Neutrino helicity

  9. Z ISm s se ISm s se Neutrino helicity

  10. Z Z  Method:Measure the direction of the circular polarization of the outgoing photons by an asymmetry experiment using NaI Result:The neutrino emitted here has negative helicity! Neutrino helicity

  11. For electrons(e) For positrons(e+) Lepton helicity Not fundamental properties of e (e+); property of weak interaction - directly related to helicity of 

  12. Lepton families Arbitrary number assignment to conserve leptons - by family! Each lepton has its own anti-lepton

  13. ?? MEGA Lepton families

  14.  at rest Note helicities of neutrinos Note: helicity of e+ due to neutrino helicities Example:  decay

  15. - at rest Note helicities of neutrinos Note: helicity of e-due to neutrino helicities Example: - decay

  16.  at rest Maximum momentum for e+ Example:  decay Minimum momentum for e+

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