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# Can NRQCD Explain the $\gamma\gamma^* \to \eta_c$ Transition Form Factor Data?

## Abstracts

 Unlike the bewildering situation in the?γγ?→π?form factor, a widespread view is that perturbative QCD can decently account for the recent \textsc{BaBar} measurement of?γγ?→ηc?transition form factor. The next-to-next-to-leading order (NNLO) perturbative correction to the?γγ?→ηc,b?form factor, is investigated in the NRQCD factorization framework for the first time. As a byproduct, we obtain by far the most precise order-α2s?NRQCD matching coefficient for the?ηc,b→γγ?process. After including the substantial negative order-α2s?correction, the good agreement between NRQCD prediction and the measured?γγ?→ηc?form factor is completely ruined over a wide range of momentum transfer squared. This eminent discrepancy casts some doubts on the applicability of NRQCD approach to hard exclusive reactions involving charmonium.
Keywords: NRQCD ;
Recommended references： Feng Feng,Yu Jia,Wen-Long Sang.(2016).Can NRQCD Explain the $\gamma\gamma^* \to \eta_c$ Transition Form Factor Data?.[ChinaXiv:201609.00930] (Click&Copy)
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