Abstract
We study the processes $e^+e^-\to\pi^+\pi^-\pi^0\pi^0\pi^0\gamma$ and $\pi^+\pi^-\pi^0\pi^0\eta\gamma$ in which an energetic photon is radiated from the initial state. The data were collected with the BaBar~ detector at SLAC. About 14\,000 and 4700 events, respectively, are selected from a data sample corresponding to an integrated luminosity of 469~$fb^{-1}$. The invariant mass of the hadronic final state defines the effective $e^+e^-$ center-of-mass energy. From the mass spectra, the first precise measurement of the $e^+e^-\to\pi^+\pi^-\pi^0\pi^0\pi^0$ cross section and the first measurement ever of the $e^+e^-\to\pi^+\pi^-\pi^0\pi^0\eta$ cross section are performed. The center-of-mass energies range from threshold to 4.35~GeV. The systematic uncertainty is typically between 10 and 13\%. The contributions from $\omega\pi^0\pi^0$, $\eta\pi^+\pi^-$, and other intermediate states are presented. We observe the $J/\psi$ and $\psi(2S)$ in most of these final states and measure the corresponding branching fractions, many of them for the first time.
Highlights
Electron-positron annihilation events with initial-state radiation (ISR) can be used to study processes over a wide range of energies below the nominal eþe− center-of-mass (c.m.) energy (Ec:m:), as proposed in Ref. [1]
To evaluate the detector acceptance and efficiency, we have developed a special package of Monte Carlo (MC)
A relatively clean sample of πþπ−3π0γ and πþπ−2π0ηγ events is selected by requiring that there be two tracks reconstructed in the drift chamber (DCH), silicon vertex tracker (SVT), or both, and seven or more photons, with an energy above 0.02 GeV, in the electromagnetic calorimeter (EMC)
Summary
Electron-positron annihilation events with initial-state radiation (ISR) can be used to study processes over a wide range of energies below the nominal eþe− center-of-mass (c.m.) energy (Ec:m:), as proposed in Ref. [1]. The calculation is most sensitive to the low-energy region, where the inclusive hadronic cross section cannot be measured reliably and a sum of exclusive states must be used. Studies of the ISR processes eþe− → μþμ−γ [6,7] and eþe− → Xhγ, using data from the BABAR experiment at SLAC, have been previously reported. Previous measurements of the eþe− → πþπ−π0π0π0 cross section were reported by the M3N [18] and MEA [19] experiments, but with very limited precision, leading to a large uncertainty in the corresponding HVP contribution. The BABAR experiment previously measured the eþe− → ηπþπ− reaction in the η → πþπ−π0 [14] and η → γγ [20] decay channels.
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