title: Can Nonrelativistic QCD Explain the γγ^{*}→η_{c} Transition Form Factor Data?
abstract: Unlike the bewildering situation in the γγ^{*}→π form factor, a widespread view is that perturbative QCD can decently account for the recent BABAR measurement of the γγ^{*}→η_{c} transition form factor. The next-to-next-to-leading-order perturbative correction to the γγ^{*}→η_{c,b} form factor, is investigated in the nonrelativistic QCD (NRQCD) factorization framework for the first time. As a byproduct, we obtain, by far, the most precise order-α_{s}^{2} NRQCD matching coefficient for the η_{c,b}→γγ process. After including the substantial negative order-α_{s}^{2} correction, the good agreement between NRQCD prediction and the measured γγ^{*}→η_{c} form factor is completely ruined over a wide range of momentum transfer squared. This eminent discrepancy casts some doubts on the applicability of the NRQCD approach to hard exclusive reactions involving charmonium.
authors.affiliation: China University of Mining and Technology, Beijing 100083, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Feng
authors.affiliation: Institute of High Energy Physics and Theoretical Physics Center for Science Facilities, Chinese Academy of Sciences, Beijing 100049, China.|Center for High Energy Physics, Peking University, Beijing 100871, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Jia
authors.affiliation: School of Physical Science and Technology, Southwest University, Chongqing 400700, China.|State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Wen-Long
authors.initials: WL
authors.lastname: Sang