# PERC - Introduction

Neutron beta decay is described by two parameters in the Standard Model of particle physics, the ratio of axial vector and vector coupling constant and the quark mixing matrix element for the first generation. However, in neutron decay many different observables can be defined, for example beta-, neutrino-, or proton asymmetry or the precise shapes of the electron or the proton spectrum. These observables are related to the parameters of the theory. Measuring them with high precision does not only allow calculating these parameters but also checking the consistency of the theory. In this way, exotic couplings like right-handed, scalar- or tensor-like can be searched for.
Presently, this research is limited experimentally at the 10 |