Precision Measurement of the e+e- --> K+K-(gamma) Cross Section with the Initial-State Radiation Method at BaBar

TL;DR

This paper presents a high-precision measurement of the e+e- to K+K-(gamma) cross section using the ISR method at BaBar, providing insights into the kaon form factor and contributions to the muon g-2 anomaly.

Contribution

It introduces a precise measurement of the K+K- cross section using ISR at BaBar, improving the understanding of hadronic contributions to muon g-2.

Findings

Measured the lowest-order hadronic vacuum polarization contribution as (22.93 ± 0.18_stat ± 0.22_syst) x 10^{-10}

Extracted the charged kaon form factor and compared it to QCD predictions

Found the form factor magnitude exceeds asymptotic QCD predictions at large energies

Abstract

A precise measurement of the cross section for the process e+e- --> K+K-(gamma) from threshold to an energy of 5 GeV is obtained with the initial-state radiation (ISR) method using 232 fb^{-1} of data collected with the BaBar detector at e+e- center-of-mass energies near 10.6 GeV. The measurement uses the effective ISR luminosity determined from the e+e- --> mu+mu-(gamma)gamma_ISR process with the same data set. The corresponding lowest-order contribution to the hadronic vacuum polarization term in the muon magnetic anomaly is found to be a_mu^{KK, LO}=(22.93 +- 0.18_{stat} +- 0.22_{syst}) * 10^{-10}. The charged kaon form factor is extracted and compared to previous results. Its magnitude at large energy significantly exceeds the asymptotic QCD prediction, while the measured slope is consistent with the prediction.