  We study the velocity autocorrelations in an experimental configuration of
confined two-dimensional active rotors (disks). We report persistent small
scale oscillations in both rotational and translational velocity
autocorrelations, with their characteristic frequency increasing as rotational
activity increases. While these small oscillations are qualitatively similar in
all experiments, we found that, at strong particle rotational activity, the
large scale particle spin fluctuations tend to vanish, with the small
oscillations around zero persisting in this case, and spins remain
predominantly and strongly anti-correlated at longer times. For weaker
rotational activity, however, spin fluctuations become increasingly larger and
angular velocities remain de-correlated at longer times. We discuss in detail
how the autocorrelation oscillations are related to the rotational activity and
why this feature is generically a signal of the emergence of chirality in the
dynamics of a particulate system.
