A STUDY OF 3- AND 4-BODY HADRONIC FINAL STATES USING INITIAL STATE RADIATION WITH BABAR

摘要

A study of several 3- and 4-body hadronic final states (π~+π~-π~0, π ~+π~-π~+π~-, K~+K~-π~+π~- and K~+K~-K~+K~-) accompanied by hard photon is presented. These states are produced from e~+ e~-collisions at the c.m. energy near Υ(4S) resonance using 90 fb~(-1) data sample collected with the BABAR detector at the PEP-II colider. The invariant mass of the hadronic final state determines the virtual photon energy, so that data can be compared with direct e~+e~- cross sections. The cross sections for the above final states have been obtained from the threshold to 4.5 GeV with about 5% systematic errors. The accuracy of the results are comparable with the best direct e~+e~- results overall and with much better precision in 1.4-2.5 GeV region where very few data are available. In addition to light meson spectroscopy these data can be used to improve the determination of R - the ratio of e~+e~- → hadrons cross section to e~+e~- → μ~+μ~- - and thereby to impact the understanding of recent (g — 2)_μ measurement. The ISR technique also gives access to J/ψ production. Measurements of branching ratios into 3- and 4-body final states given above are made to a level of precision that is tipically better than that obtained in the combined earlier measurements.