Exclusive Two-Vector-Meson Production from e^+ e^- Annihilation

TL;DR

This work studies exclusive $e^+e^-$ annihilation into pairs of vector mesons with $J^{PC}=1^{--}$, showing that at high beam energy the process is fragmentation-dominated via $\gamma^*\gamma^*$ leading to independent vector-meson production. It provides explicit fragmentation-based cross sections and angular distributions, and then adds NRQCD-based nonfragmentation corrections for charmonium pairs, highlighting sizable interference effects. The results are confronted with BaBar and Belle data, showing consistency within experimental cuts and uncertainties, and suggesting the potential for observing $J/\psi+J/\psi$ at current $B$-factories. Overall, the paper clarifies the relative importance of fragmentation, nonfragmentation, and interference contributions and offers updated NRQCD inputs that influence the predicted rates for double-charmonium production.

Abstract

The exclusive production of pairs of vector mesons with J^{PC} = 1^{--} in e^+ e^- collisions can proceed through e^+ e^- annihilation into two virtual photons. At energies much greater than the meson masses, the cross section is dominated by the independent fragmentation of the virtual photons into the vector mesons. The fragmentation approximation is used to calculate the cross sections and angular distributions for pairs of vector mesons that can be produced at the B factories. The predicted cross sections for rho^0 + rho^0 and rho^0 + phi production agree with recent measurements by the BaBar Collaboration. For the production of two charmonium vector mesons, the nonfragmentation corrections to the cross sections are calculated by using the NRQCD factorization formalism. The predicted cross sections for J/psi + J/psi and J/psi + psi(2S) production are compatible with upper limits set by the Belle Collaboration.

Figures (3)

• Figure 1: QED fragmentation diagrams that contribute to exclusive two-vector-meson production in $e^+ e^-$ collisions if the two vector mesons have quark contents $q \bar{q}$ and $q' \bar{q}'$.
• Figure 2: QED nonfragmentation diagrams that contribute to exclusive two-vector-meson production in $e^+ e^-$ collisions if the two vector mesons have the same quark content $q \bar{q}$.
• Figure 3: Differential cross sections $d\sigma/d|x|$ for $e^+ e^-$ annihilation into $V_1+V_2$ at $E_{\rm beam}= 5.29$ GeV, where $V_i= \rho^0$, $\phi$, or $J/\psi$. The areas under the curves are the total cross sections.