Abstract
The two-photon physics program of the BESIII Collaboration is mainly motivated by the need of new measurements of transition form factors as input for the Standard Model calculations of $ \mathop a\nolimits_\mu ^{HLbL} $, the hadronic light-by-light scattering contribution to the anomalous magentic moment of the muon. The large data sets acquired at BESIII allow to study the transition form factors of pseudoscalar mesons in the relevant region of momentum transfer for $ \mathop a\nolimits_\mu ^{HLbL} $. In this presentation the status of the respective measurements for π0,η and η’ mesons are discussed, and prospects for studies of multi-meson systems as well as of doubly-virtual transition form factors are given.
Highlights
Transition form factors (TFF) describe the coupling of photons and hadronic matter
The two-photon physics program of the BESIII Collaboration is mainly motivated by the need of new measurements of transition form factors as input for the Standard Model calculations of aHμ LbL, the hadronic light-by-light scattering contribution to the anomalous magentic moment of the muon
The large data sets acquired at BESIII allow to study the transition form factors of pseudoscalar mesons in the relevant region of momentum transfer for aHμ LbL
Summary
Transition form factors (TFF) describe the coupling of photons and hadronic matter. More precisely, they describe the deviation from the point-like interaction of two photons and mesons as described by quantum electrodynamics (QED). Since experimental information on the respective observables is rather scarce, hadronic models have been used in the calculations [2, 11], which in turn introduce a model dependency in the uncertainty estimate of aμHLbL. This fact, as well as the recent results and the prospects of so-called “meson factories” have fostered the development of data-driven approaches [12]. As the differential cross section of two-photon collisions has its maximum at smallest momentum transfers of the scattered leptons, the kinematic region, in which the TFF can be studied, is mostly limited by the detector acceptance and the acquired statistics. This presentation focuses on the investigations in two-photon collisions
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