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In fast wind or when the local Coulomb collision frequency is low,observations show that solar wind minor ions and ion sub-populations flow withdifferent bulk velocities. Measurements indicate that the drift speed of bothalpha particles and proton beams with respect to the bulk or core protonsrarely exceeds the local Alfv\'en speed, suggesting that a magnetic instabilityor other wave-particle process limits their maximum drift. We comparesimultaneous alpha particle, proton beam, and proton core observations frominstruments on the Wind spacecraft spanning over 20 years. In nearlycollisionless solar wind, we find that the normalized alpha particle driftspeed is slower than the normalized proton beam speed; no correlation betweenfluctuations in both species' drifts about their means; and a stronganti-correlation between collisional age and alpha-proton differential flow,but no such correlation with proton beam-core differential flow. Controllingfor the collisional dependence, both species' normalized drifts exhibit similarstatistical distributions. In the asymptotic, zero Coulomb collision limit, theyoungest measured differential flows most strongly correlate with anapproximation of the Alfv\'en speed that includes proton pressure anisotropy.In this limit and with this most precise representation, alpha particles driftat 67% and proton beam drift is approximately 105% of the local Alfv\'en speed.We posit that one of two physical explanations is possible. Either (1) anAlfv\'enic process preferentially accelerates or sustains proton beams and notalphas or (2) alpha particles are more susceptible to either an instability orCoulomb drag than proton beams.

A comparison of Alpha Particle and Proton Beam Differential flow in Collisionally Young Solar Wind