Recoil and Power Corrections in High-xT Direct-Photon Production

We study a class of nonperturbative corrections to single-inclusive photon cross sections at measured transverse momentum pT , in the large-xT limit. We develop an extension of the joint (threshold and transverse momentum) resummation formalism, appropriate for large xT , in which there are no kinematic singularities associated with recoil, and for which matching to fixed order and to threshold resummation at next-to-leading logarithm (NLL) is straightforward. Beyond NLL, we find contributions that can be attributed to recoil from initial state radiation. Associated power corrections occur as inverse powers of pT and are identified from the infrared structure of integrals over the running coupling. They have significant energy dependence and decrease from typical fixed-target to collider energies. Energy conservation, which is incorporated into joint resummation, moderates the effects of perturbative recoil and power corrections for large xT .