Predictive power of transverse-momentum-dependent distributions

We investigate the predictive power of transverse-momentum-dependent (TMD) distributions as a function of the light-cone momentum fraction x and the hard scale Q defined by the process. We apply the saddle-point approximation to the unpolarized quark and gluon transverse momentum distributions and evaluate the position of the saddle point as a function of the kinematics. We determine quantitatively that the predictive power for an unpolarized transverse momentum distribution is maximal in the large-Q and small-x region. For cross sections the predictive power of the TMD factorization formalism is generally enhanced by considering the convolution of two distributions, and we explicitly consider the case of Z and H^0 boson production. In the kinematic regions where the predictive power is not maximal, the distributions are sensitive to the nonperturbative hadron structure. Thus, these regions are critical for investigating hadron tomography in a three-dimensional momentum space.