By: Christopher Hayes November 29, 2012 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 Also works for neutron decay and muon decay Historical document---First succesful theory of the creation of massive particles

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

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

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

Decay Distribution and Lifetime

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

Calculation of Lifetime Δ = 2.5%

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.