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

Abstract

6We study the process e + e − → π + π − π + π − γ, 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 e + e − center-of-mass energy, so that these data can be compared with the corresponding direct e + e − measurements. From the 4π-mass spectrum, the cross section for the process e + e − → π + π − π + π − is measured for center-of-mass energies from 0.6 to 4.5 GeV. The uncertainty in the cross section measurement is typically 5%. We also measure the cross sections for the final statesWe observe the J/ψ in all three final states and measure the corresponding branching fractions. We search for X(3872) in J/ψ(→ µ + µ − )π + π − and obtain an upper limit on the product of the e + e − width of the X(3872) and the branching fraction for X(3872) → J/ψπ + π − .