Measurement of the charged-pion polarisability

Abstract

The COMPASS collaboration at CERN has investigated pion Compton scattering, ${\pi }^{-}\gamma \to {\pi }^{-}\gamma$, at centre-of-mass energy below 3.5 pion masses. The process is embedded in the reaction ${\pi }^{-}\mathrm{Ni}\to {\pi }^{-}\gamma \mathrm{Ni}$, which is initiated by 190\,GeV pions impinging on a nickel target. The exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, $Q^2<0.0015$\,(GeV/$c$)${}^2$. From a sample of 63\,000 events the pion electric polarisability is determined to be $α_π =\ (\,2.0\ \pm\ 0.6_{\mbox{\scriptsize stat}}\ \pm\ 0.7_{\mbox{\scriptsize syst}}\,) \times 10^{-4}\,\mbox{fm}^3$ under the assumption ${\alpha }_{\pi }=-{\beta }_{\pi }$, which relates the electric and magnetic dipole polarisabilities. It is the most precise measurement of this fundamental low-energy parameter of strong interaction, that has been addressed since long by various methods with conflicting outcomes. While this result is in tension with previous dedicated measurements, it is found in agreement with the expectation from chiral perturbation theory. An additional measurement replacing pions by muons, for which the cross-section behavior is unambigiously known, was performed for an independent estimate of the systematic uncertainty.

Published version: 9 pages, 3 figures, 1 table

References in corpus (7)

• The COMPASS Experiment at CERN
• Revisiting γγ->π^+π^- at low energies
• Cross sections for low-energy ${\pi }^{-}\gamma$ reactions
• The polarizability of the pion: no conflict between dispersion theory and chiral perturbation theory
• Radiative corrections to pion Compton scattering
• Radiative Corrections to High Energy Lepton Bremsstrahlung on Heavy Nuclei
• Radiative corrections to real and virtual muon Compton scattering revisited

Cited by in corpus (11)

• Anomalous decay and scattering processes of the eta meson
• Pion light-by-light contributions to the muon $g-2$
• The hadronic light-by-light contribution to the muon's anomalous magnetic moment
• Compton Scattering off Pions and Electromagnetic Polarizabilities
• Chiral extrapolation of the charged-pion magnetic polarizability with Padé approximant
• Dipole polarizabilities of charged pions
• Polarizabilities from kaon Compton scattering
• Dipole polarizabilities of light pseudoscalar mesons within the Domain Model of QCD vacuum
• Tests of Three-Flavor Chiral Perturbation Theory
• Study of the Transverse-Momentum-Dependent structure of the nucleon in Semi-Inclusive DIS
• Search for Axion Like Particles produced via the Primakoff process at COMPASS