https://doi.org/10.1140/epjc/s10052-019-7453-5
Regular Article - Theoretical Physics
A new angle on an old problem: helicity approach to neutron beta decay in the Standard Model
1
Füüsika Instituut, Tartu Ülikool, W. Ostwaldi 1, 50411, Tartu, Estonia
2
PRISMA+ Cluster of Excellence, Institut für Physik, Johannes Gutenberg-Universität, 55099, Mainz, Germany
3
Division of Theoretical Physics, Institut Rudjer Bošković, Bijenička 54, 10000, Zagreb, Croatia
* e-mail: groote@ut.ee
Received:
1
October
2019
Accepted:
1
November
2019
Published online:
20
November
2019
We elaborate on the dichotomy between the description of the semileptonic decays of heavy hadrons on the one hand and the semileptonic decays of light hadrons such as neutron 
decays on the other hand. For example, almost without exception the semileptonic decays of heavy baryons are described in cascade fashion as a sequence of two two-body decays 
and 
whereas neutron decays are analyzed as true three-body decays 
. Within the cascade approach it is possible to define a set of seven angular observables for polarized neutron decays as well as the longitudinal, transverse and normal polarization of the decay electron. We determine the dependence of the observables on the usual vector and axial vector form factors. In order to be able to assess the importance of recoil corrections we expand the rate and the 
averages of the observables up to NLO and NNLO in the recoil parameter 
. Remarkably, we find that the rate and three of the four parity conserving polarization observables that we analyze are protected from NLO recoil corrections when the second class current contributions are set to zero.
© The Author(s), 2019
