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Neutron Beta Decay

Neutron Beta Decay. By: Christopher Hayes November 29, 2012. Fermi’s Original Theory. First Theory of beta decay developed by Fermi (1933) Point-like four fermion vertex Could be applied to any nucleus. Also works for neutron decay and muon decay

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Neutron Beta Decay

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  1. NeutronBetaDecay By: Christopher Hayes November 29, 2012

  2. Fermi’s Original Theory • First Theory of beta decay developed by • Fermi (1933) • Point-like four fermion vertex • Could be applied to any nucleus. Also works for neutron decay and muon decay • Historical document---First succesful theory of the creation of massive particles

  3. Muon Decay • Theory of muon decay is similar to neutron beta decay • Muon decay is a pure weak interaction ---defines the strength of the weak coupling constant • Precision of GF determined by precision of muon lifetime calculation

  4. First Order Calculation of Neutron Decay Rate • Treats neutron and proton as point-like • Dirac particles which couple to W -- • Feynman Diagram similar to muon decay • Matrix element exactly the same as muon decay

  5. Matrix Element Propagator for a massive vector boson: Weak force V-A vertex factor: Matrix Element:

  6. Decay Distribution and Lifetime

  7. Theory of Neutron Decay with Spectator Quarks • Presence of spectator quarks modifies the calculation of the matrix element at the quark-quark vertex • Generational mixing at the quark-quark vertex requires and additional factor of Vud from the CKM matrix

  8. Calculation of Lifetime Δ= 2.5%

  9. Further extensions of the theory of neutron beta decay • More sophisticated theory includes terms which couple directly to the neutron spin vector. • Particle Data Booklet lists values for a, A, B, D • Constants A,B, D determined by experiments with polarized neutrons • Nab experiment at SNS will measure the constants a, b.

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