  As part of a programme to develop parton showers with controlled logarithmic
accuracy, we consider the question of collinear spin correlations within the
PanScales family of parton showers. We adapt the well-known Collins-Knowles
spin-correlation algorithm to PanScales antenna and dipole showers, using an
approach with similarities to that taken by Richardson and Webster. To study
the impact of spin correlations, we develop Lund-declustering based observables
that are sensitive to spin-correlation effects both within and between jets and
extend the MicroJets collinear single-logarithmic resummation code to include
spin correlations. Together with a 3-point energy correlation observable
proposed recently by Chen, Moult and Zhu, this provides a powerful set of
constraints for validating the logarithmic accuracy of our shower results. The
new observables and their resummation further open the pathway to
phenomenological studies of these important quantum mechanical effects.
