Pion polarizability status report

Research output: Contribution to conferencePaperpeer-review

Abstract

The electric απ and magnetic βπ charged pion Compton polarizabilities are of fundamental interest in the low-energy sector of quantum chromodynamics (QCD). They are directly linked to the phenomenon of spontaneously broken chiral symmetry within QCD and to the chiral QCD lagrangian. The combination (αππ) was measured by: (1) CERN COMPASS via radiative pion Primakoff scattering (Bremsstrahlung) in the nuclear Coulomb field, π-Z → π-Zγ, (2) SLAC PEP Mark-II via two-photon production of pion pairs, γγ→π+π-, and (3) Mainz Microtron MAMI via radiative pion photoproduction from the proton, γp → γπ+π. COMPASS and Mark-II agree with one another: (1) αππ = (4.0±1.2stat±1.4syst)×10-4fm3, (2) αππ = (4.4±3.2stat+syst) ×10-4 fm3. The Mainz value (3) αππ = (11.6 ± 1.5stat ± 3.0syst ± 0.5model) ×10-4fm3 is excluded on the basis of a dispersion relations calculation which uses the Mainz value as input, and gives significantly too large γγ→π0π0 cross sections compared to DESY Crystal Ball data. COMPASS and Mark-II polarizability values agree well with the two-loop chiral perturbation theory (ChPT) prediction αππ = (5.7±1.0)×10-4 fm3, thereby strengthening the identification of the pion with the Goldstone boson of QCD.

Original languageEnglish
StatePublished - 2017
Event2017 Meeting of the APS Division of Particles and Fields, DPF 2017 - Batavia, United States
Duration: 31 Jul 20174 Aug 2017

Conference

Conference2017 Meeting of the APS Division of Particles and Fields, DPF 2017
Country/TerritoryUnited States
CityBatavia
Period31/07/174/08/17

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