Beta spectrum of unique first-forbidden decays as a novel test for fundamental symmetries

Understand

Within the Standard Model, the weak interaction of quarks and leptons is characterized by certain symmetry properties, such as maximal breaking of parity and favored helicity.

• These are related to the $V-A$ structure of the weak interaction.
• These characteristics were discovered by studying correlations in the directions of the outgoing leptons in nuclear beta decays.
• These days, correlation measurements in nuclear beta decays are intensively studied to probe for signatures for deviations from these symmetries, which are an indication of Beyond Standard Model physics.