Testing Charmonium Production Mechanism via Polarized $J/\psi$ Pair Production at the LHC

TL;DR

This paper proposes that polarized double charmonium production at the LHC can effectively distinguish between color-singlet and color-octet mechanisms in charmonium production, especially at high transverse momentum.

Contribution

It introduces polarization measurements of $J/\psi$ pairs as a novel test to differentiate charmonium production mechanisms in NRQCD.

Findings

Color-octet mechanism predicts mostly transversely polarized $J/\psi$ pairs at high $p_T$.

Color-singlet mechanism results in about half of pairs with at least one longitudinally polarized $J/\psi$.

Polarized $J/\psi$ pair production is experimentally feasible at the LHC.

Abstract

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