  The necessicity of the color-octet mechanism in describing heavy quarkonium
production is a longstanding puzzle. Compared to the yields of heavy
quarkonium, its polarizations should be a sensitive observable to pin down the
color-octet contributions. In this talk, I will focus on the $\chi_c$
polarization in hadroproduction processes, which may provide a unique test for
the color-octet mechanism in nonrelativistic QCD.
