Uncertainty of polarized gluon distribution from prompt photon production

Constraint of prompt photon data on the polarized gluon distribution is discussed in terms of uncertainty estimation for polarized parton distribution functions (PDFs). By comparing between uncertainty of the double spin asymmetry A_{LL}^\gamma and expected statistical errors at RHIC, we found that the gluon distribution is effectively constrained in the region 0.04<x_{_T}<0.2 with the data at transverse momentum p_{_T}=10-20 GeV for center-of-mass energies \sqrt{s}=200 and 500 GeV.