  We show the evidence of ion-cyclotron dissipation mechanism in solar wind
plasma using Helios data. From our statistical analysis we found that the wave
power of high-frequency transverse waves (having frequencies between 0.01 and 1
normalized to the proton gyrofrequency in the plasma frame) correlates with
both, the proton temperature anisotropy, $T_{\perp}/T_{\parallel}$, and the
normalized differential speed, $V_{\alpha p}/V_A$, between alpha particles and
protons. Furthermore, when this speed stays below 0.5, then the alpha-particle
temperature anisotropy correlate positively with the relative power of the
transverse waves. However, if $V_{\alpha p}/V_A$ is larger than 0.6, then the
alpha-particle temperature anisotropy tends to decrease towards values below
unity, despite the presence of transverse waves with relatively large
amplitudes. For small relative wave amplitude, it is found that alpha particles
can even be heated more strongly than protons when the alpha-to-electron
density ratio nearly or below 0.01. Our findings are in good agreement with
predictions of kinetic theory for the resonant interaction of ions with
Alfv\'en-cyclotron waves and for the resulting wave dissipation. Also, the
study suggests that the turbulence could lead to the generation of parallel
Alfven cyclotron waves.
