The $\epem\to\pi^+\pi^-\pi^+\pi^-$, $K^+K^-\pi^+\pi^-$, and $K^+K^- K^+K^- $ Cross Sections at Center-of-Mass Energies 0.5--4.5 \gev Measured with Initial-State Radiation

TL;DR

This paper measures the cross sections of specific e+e- annihilation processes involving multiple mesons over a range of energies using initial-state radiation data from BaBar, providing detailed insights into hadronic interactions and resonance structures.

Contribution

First measurement of these cross sections across 0.6 to 4.5 GeV, including observation of J/psi and setting limits on X(3872) production, with high precision data analysis.

Findings

Measured e+e- to 4π, K+K-π+π-, and K+K-K+K- cross sections from 0.6 to 4.5 GeV.

Observed J/ψ in all three final states and determined their branching fractions.

Set an upper limit on X(3872) production in e+e- collisions.

Abstract

We study the process $e^+e^-\to\pi^+\pi^-\pi^+\pi^-\gamma$, with a hard photon radiated from the initial state. About 60,000 fully reconstructed events have been selected from 89 $fb^{-1}$ of BaBar data. The invariant mass of the hadronic final state defines the effective \epem center-of-mass energy, so that these data can be compared with the corresponding direct $e^+e^-$ measurements. From the $4\pi$-mass spectrum, the cross section for the process $e^+e^-\to\pi^+\pi^-\pi^+\pi^-$ is measured for center-of-mass energies from 0.6 to 4.5 $GeV/c^2$. The uncertainty in the cross section measurement is typically 5%. We also measure the cross sections for the final states $K^+ K^- \pi^+\pi^-$ and $K^+ K^- K^+ K^-$. We observe the $J/\psi$ in all three final states and measure the corresponding branching fractions. We search for X(3872) in $J/\psi (\to\mu^+\mu^-) \pi^+\pi^-$ and obtain an upper limit on the product of the $e^+e^-$ width of the X(3872) and the branching fraction for $X(3872) \to J/\psi\pi^+\pi^-$.