Study of $\ep\en$ Collisions in the 1.5-3 Gev C.M. Energy Region Using Isr at \babar

Abstract

A preliminary analysis of low-energy $\ep\en$ collision data produced via initial state radiation (ISR) has been performed using 22 $fb^{-1}$ of \babar \~data. The selection of data samples corresponding to the $\mumu$, $\pipi$, $\kk$, $p \bar p$, $\kk\pi^0$, 3$\pi$, 4$\pi$, 5$\pi$, 6$\pi$, 7$\pi$ final states accompanied by the emitted ISR hard photon has been demonstrated. The invariant mass of the hadronic final state defines the effective collision c.m. energy, and so \babar ISR data can be compared to the relevant direct $\ep\en$ measurements. The resulting distributions are already competitive with DCI and ADONE data in the 1.4-3.0 GeV energy range. In particular, they do not suffer from the relative normalization uncertainties observed for certain reactions when results from different experiments are combined. Eventually, such data may be used to measure the energy dependence of R, the ratio of the $\ep\en\to hadrons$ and $\ep\en\to\mumu$ cross sections, in the low-energy regime where precise measurements will have an impact on the interpretation of the new $(g-2)_{\mu}$ measurements.