# Precision experiments in beta decay

Beta-decay offers a convenient and proven way to investigate the standard model of the electroweak interaction. In fact, experiments in beta decay were one of the pillars on which the standard model was built. However, in order to compete with high energy physics experiments the precision of beta decay experiments has to be increased continously, making use of the latest technologies.

4-point interaction/Hamiltonian link

The decay probability, or decay rate, for beta decay is derived from Fermis Golden Rule

... Fermis golden Rule (coupling constant, matrix element, phase space factor, some constants)

When only looking for the dependence on the beta energy, the well-known shape of the beta spectrum results:

... beta spectrum without correlations

where Vud describes ...

when also looking at the particle momenta and spins, correlations between these arise:

JTW equations

pick one, and explain what all can be tested

Symmetries, Vud/unitarity of CKM matrix, coupling constants, search for exotic interactions (S,T,P)

Cx/Cv strenght of interaction x compared to the vector interaction

For more in-depth details see RMP