Testing charmonium production mechanism via the polarized J/ψ pair production at the LHC

At present the color-octet mechanism is still an important and debatable part in non-relativistic QCD (NRQCD). In this work we find that the polarized double charmonium production at the LHC may pose a stringent test on the charmonium production mechanism. The result shows that the transverse momentum (pT) scaling behavior of double J/ψ differential cross sections in color-singlet and -octet production mechanisms deviates distinctively from each other when pT is larger than 7 GeV. In the color-octet mechanism, the two J/ψs in one pair are mostly transversely polarized when pT 2mc, as expected from the fragmentation limit point of view. In the color-singlet mechanism, there is about one-half of the charmonium pairs with at least one J/ψ being longitudinally polarized at a moderate transverse momentum. The energy dependence of the polarized J/ψ pair production is found to be weak, and this process is found to be experimentally attainable in the early phase of the LHC operation.

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