Prompt J/Psi production at LHC: new evidence for the kt-factorization

TL;DR

This paper tests the color-singlet mechanism within the $k_T$-factorization framework for prompt $J/psi$ production at $\sqrt{s}=7$ TeV, including direct and feed-down contributions from $\chi_{c1,2}$ and $\psi^\prime$. Using off-shell matrix elements and unintegrated gluon densities from ${\rm CCFM}$ and ${\rm KMR}$, the authors achieve good agreement with CMS, ATLAS and LHCb data, with feed-down essential at high $p_T$. They also predict three polarization parameters $\lambda_\theta$, $\lambda_\phi$, and $\lambda_{\theta \phi}$ in two reference frames and find no need for color-octet contributions in this setup. The results suggest that LO $k_T$-factorization effectively captures higher-order effects and provide a robust framework for quarkonium production studies and model discrimination at the LHC.

Abstract

In the framework of the kt-factorization approach, the production and polarization of prompt J/Psi mesons in pp collisions at the LHC energy 7 TeV is studied. Both the direct production mechanism as well as feed-down contributions from chic1, chic2 and psi' decays are taken into account. Our consideration is based on the color singlet model supplemented with the off-shell matrix elements for the corresponding partonic subprocesses. The unintegrated gluon densities in a proton are determined using the CCFM evolution equation as well the Kimber-Martin-Ryskin prescription. We compare our numerical predictions with the first experimental data taken by the CMS, ATLAS and LHCb collaborations. The estimation of all polarization parameters which determine J/Psi spin density matrix is performed.

Figures (3)

• Figure 1: The double differential cross sections $d\sigma/dydp_T$ of prompt $J/\psi$ production at $\sqrt s = 7$ TeV compared to the CMS data26. The solid, dashed and dash-dotted curves correspond to the results obtained using the CCFM A0, CCFM B0 and KMR gluon densities, respectively. The dotted curves represent the contribution from sole direct production mechanism calculated with the CCFM A0 gluon distribution.
• Figure 2: The double differential cross sections $d\sigma/dydp_T$ of prompt $J/\psi$ production at $\sqrt s = 7$ TeV compared to the ATLAS data27. Notation of all histograms is the same as in Fig. 1.
• Figure 3: The double differential cross sections $d\sigma/dydp_T$ of prompt $J/\psi$ production at $\sqrt s = 7$ TeV compared to the LHCb data28. Notation of all histograms is the same as in Fig. 1.