ISR Hadron Production in e+e- Annihilations and Meson-Photon Transition Form Factors

TL;DR

This paper reports on BaBar collaboration results involving meson production, transition form factors, and their implications for understanding meson structures, QCD tests, and muon magnetic moment calculations.

Contribution

It provides new measurements of meson transition form factors and processes, offering insights into meson structures and QCD models, and improves understanding of the Y(2175) meson and muon anomalous magnetic moment.

Findings

Improved understanding of Y(2175) meson from e+e- processes.

Precise measurements of pi+pi- process enhance muon g-2 calculations.

Discrepancies observed in pi0 transition form factor compared to expectations.

Abstract

We present several recent results from the BaBar collaboration in the areas of initial state radiation physics and transition form factors. An updated study of the processes e+e- -> K+K-pi+pi- and e+e- -> K+K-pi0pi0 provides an improved understanding of the Y(2175) meson. A very precise study of the process e+e- -> pi+pi- improves the precision on the calculated anomalous magnetic moment of the muon and provides by far the best information on excited rho states. Our previous measurements of the timelike transition form factors (TFF) of the eta and eta' mesons at Q^2=112 GeV^2, combined with new measurements of the their spacelike TFFs and those of the pi0 and eta_c mesons, provide powerful tests of QCD and models of the distribution amplitudes of quarks inside these mesons. The eta_c TFF shows the expected behavior over the Q^2 range 1-50 GeV^2, and we are sensitive to next-to-leading-order QCD corrections. The eta and eta' TFFs are consistent with expected behavior, but those for the pi0 are not. Extracting the strange and nonstrange components of the eta and eta' TFFs, we find the nonstrange component to be consistent with theoretical expectations and inconsistent with the measured pi0 TFF.