Measurement of the e+e- --> hadrons cross-section at low energy with ISR events at BABAR

TL;DR

This paper reports a precise measurement of the e+e- to hadrons cross section at low energies using ISR events at BABAR, providing important data for muon g-2 calculations and hadronic cross sections.

Contribution

It introduces a method to measure low-energy hadronic cross sections with ISR at BABAR, improving the precision of these measurements for muon g-2 calculations.

Findings

Measured e+e- to pi+ pi- cross section from threshold to 3 GeV.

Calculated the hadronic contribution to muon magnetic anomaly as (514.1 +- 2.2(stat) +- 3.1(syst)) * 10^{-10}.

Presented additional ISR multihadronic cross section results.

Abstract

The precise measurement of the cross section e+e- --> pi+ pi-(gamma) from threshold to an energy of 3 GeV, using events with Initial State Radiation (ISR) collected with the BABAR detector, is presented. The ISR luminosity is determined from a study of the leptonic process e+e- --> mu+ mu- gamma(gamma), and the method is tested by the comparison with the next-to-leading order (NLO) QED prediction. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the BABAR pi pi cross section measured from threshold to 1.8 GeV is (514.1 +- 2.2(stat) +- 3.1(syst)) * 10^{-10}. Other results on ISR multihadronic cross sections from BABAR are presented.