title: η(c) production at LHC and implications for the understanding of J/ψ production.
abstract: We present a complete evaluation for the prompt η_{c} production at the LHC at next-to-leading order in α_{s} in nonrelativistic QCD. By assuming heavy-quark spin symmetry, the recently observed η_{c} production data by LHCb results in a very strong constraint on the upper bound of the color-octet long-distance matrix element ⟨O^{J/ψ}(^{1}S_{0}^{[8]})⟩ of J/ψ. We find this upper bound is consistent with our previous study of the J/ψ yield and polarization and can give good descriptions for the measurements, but the upper bound is inconsistent with some other theoretical estimates. This may provide important information for understanding the nonrelativistic QCD factorization formalism.
authors: School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China.
authors: Hao
authors: H
authors: Han
authors: Maryland Center for Fundamental Physics, University of Maryland, College Park, Maryland 20742, USA.|Center for High Energy Physics, Peking University, Beijing 100871, China.
authors: Yan-Qing
authors: YQ
authors: Ma
authors: School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China.
authors: Ce
authors: C
authors: Meng
authors: School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China.|Physics Department, Theory Unit, CERN, CH-1211 Geneva 23, Switzerland.
authors: Hua-Sheng
authors: HS
authors: Shao
authors: School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China.|Center for High Energy Physics, Peking University, Beijing 100871, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100871, China.
authors: Kuang-Ta
authors: KT
authors: Chao