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.
Highlights
With heavy-quark spin symmetry (HQSS), we find that the ηc production data are compatible with our previous studies [2,5] and may provide a further constraint on the possible values of J=ψ long-distance matrix elements (LDMEs)
LDMEs estimated by the relations and the SDCs calculated up to next-to-leading order (NLO) in αs, we show the sizes of the contributions from these channels in Fig. 1, all of which are smaller than that for the CS channel by about 1 or 2 orders of magnitude, as expected
Summary.—Within NLO nonrelativistic QCD (NRQCD), we demonstrate that only 1S1⁄201 and 3S1⁄218 channels are essential for the ηc production at LHC
Summary
For the J=ψ production, with a relatively large pT cutoff (pT > 7 GeV), our group found that [2] only two linear combinations of the three CO LDMEs can be well constrained by fitting the CDF data [12] of the yields of J=ψ production, which gives week ending 6 MARCH 2015 Based on Eq (2), assuming all CO LDMEs to be positive, we updated our results for the polarization of direct J=ψ production together with that of the feeddown contributions from χc and ψð2SÞ in Ref.
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