  The dissipation of magnetized turbulence is fundamental to understanding
energy transfer and heating in astrophysical systems. Collisionless
interactions, such as resonant wave-particle process, are known to play a role
in shaping turbulent astrophysical environments. Here, we present evidence for
the mediation of turbulent dissipation in the solar wind by ion-cyclotron
waves. Our results show that ion-cyclotron waves interact strongly with
magnetized turbulence, indicating that they serve as a major pathway for the
dissipation of large-scale electromagnetic fluctuations. We further show that
the presence of cyclotron waves significantly weakens observed signatures of
intermittency in sub-ion-kinetic turbulence, which are known to be another
pathway for dissipation. These observations results suggest that in the absence
of cyclotron resonant waves, non-Gaussian, coherent structures are able to form
at sub-ion-kinetic scales, and are likely responsible for turbulent heating. We
further find that the cross helicity, i.e. the level of Alfv\'enicity of the
fluctuations, correlates strongly with the presence of ion-scale waves,
demonstrating that dissipation of collisionless plasma turbulence is not a
universal process, but that the pathways to heating and dissipation at small
scales are controlled by the properties of the large-scale turbulent
fluctuations. We argue that these observations support the existence of a
helicity barrier, in which highly Alfv\'enic, imbalanced, turbulence is
prevented from cascading to sub-ion scales thus resulting in significant
ion-cyclotron resonant heating. Our results may serve as a significant step in
constraining the nature of turbulent heating in a wide variety of astrophysical
systems.

Space Physics;Solar and Stellar Astrophysics;Plasma Physics