Beyond leading-order perturbative QCD corrections to γγ→M+M−(M=π,K)

Next-to-leading-order perturbative QCD predictions are obtained for the two-photon exclusive channels γγ→$M^{+}$ $M^{\mathrm{-}}$ (M=π,K) at large momentum transfer. The calculation is carried out in the Feynman gauge. The dimensional-regularization method is used to control both ultraviolet and infrared divergences. The model meson distribution amplitude ${\Phi }_M$∝δ(x-(1/2)) is utilized as a candidate form for the nonperturbative dynamical input. In order to reduce the effect of the particular choice of ${\Phi }_M$, similarity between γγ→$M^{+}$ $M^{\mathrm{-}}$ and ${\gamma }^{\mathrm{*}}$→$M^{+}$ $M^{\mathrm{-}}$ (timelike meson electromagnetic form factor) is employed. In the modified minimal-subtraction (MS¯) scheme definition of ${\alpha }_s$, renormalized at $W_{\gamma \gamma }$ (total center-of-mass energy of the γγ system), and with the present estimates of ${\Lambda }_{\mathrm{MS}\mathrm{¯}}$ (∼150 MeV), it is found that next-to-leading-order corrections become sufficiently small (<25%) only for $W_{\gamma \gamma }$>10 GeV, which is much larger than the highest $W_{\gamma \gamma }$ for which experimental data exist.