Tensor-polarized quark and antiquark distribution functions in a spin-one hadron

To understand orbital-angular-momentum contributions is becoming crucial for clarifying nucleon-spin issue in the parton level. Twist-two structure functions b_1 and b_2 for spin-one hadrons could probe orbital-angular-momentum effects, which reflect a different aspect from current studies for the spin-1/2 nucleon, since they should vanish if internal constituents are in the S state. These structure functions are related to tensor structure in spin-one hadrons. Studies of such tensor structure will open a new field of high-energy spin physics. The structure functions b_1 and b_2 are described by tensor-polarized quark and antiquark distributions delta_T-q and delta_T-qbar. Using HERMES data on the b_1 structure function for the deuteron, we made an analysis of extracting the distributions delta_T-q and delta_T-qbar in a simple x-dependent functional form. Optimum distributions are proposed for the tensor-polarized valence and antiquark distribution functions from the analysis. A finite tensor polarization is obtained for antiquarks if we impose a constraint that the first moments of tensor-polarized valence-quark distributions vanish. It is interesting to investigate a physics mechanism to create a finite tensor-polarized antiquark distribution.