Diffractive Vector-Meson Production from the Light-Front Quark Model

Abstract

We study exclusive diffractive electroproduction of the ${\rho }^0$, $\varphi$, $J/\psi$, and $\psi (2S)$ mesons in the color-dipole picture using two spin-orbit light-front wave functions, S-1 and S-2. S-1 follows from the Melosh--Wigner rotation in the light-front quark model (LFQM), while S-2 is the spin-improved form commonly used in holographic and boosted-Gaussian approaches. Both share the same radial wave function, with their parameters determined from the LFQM Hamiltonian. The color-glass-condensate dipole parameters are fixed from inclusive structure-function data, with no fit to diffractive data. We compare the predictions with measurements of cross sections, $R={\sigma }_L/{\sigma }_T$, $t$ and $W$ dependences, and ${\sigma }_{\varphi }/{\sigma }_{\rho }$. S-1 gives a better description of the light-meson observables, while S-2 provides a better description of the charmonium ratio ${\sigma }_{\psi (2S)}/{\sigma }_{J/\psi }$ and the $J/\psi$ decay constant. We also present the charge, magnetic, and quadrupole form factors of the four mesons and compare them with available lattice-QCD results.

arXiv comment20 pages, 14 figures