TY - JOUR
T1 - Compton scattering off pions and electromagnetic polarizabilities
AU - Moinester, Murray
AU - Scherer, Stefan
N1 - Publisher Copyright:
© 2019 World Scientific Publishing Company.
PY - 2019/6/10
Y1 - 2019/6/10
N2 - The electric (απ) and magnetic (βπ) Compton polarizabilities of both the charged and the neutral pion are of fundamental interest in the low-energy sector of quantum chromodynamics (QCD). Pion polarizabilities affect the shape of the γπ → γπ Compton scattering angular distribution at back scattering angles and γγ → ππ absolute cross sections. Theory derivations are given for the γπ → γπ Compton scattering differential cross section, dispersion relations, and sum rules in terms of the polarizabilities. We review experimental charged and neutral polarizability studies and theoretical predictions. The π0 polarizabilities were deduced from DESY Crystal Ball γγ → π0π0 data, but with large uncertainties. The charged pion polarizabilities were deduced most recently from (1) radiative pion Primakoff scattering π-Z → π-Zγ at CERN COMPASS, (2) two-photon pion pair production γγ → π+π- at SLAC Mark II, and (3) radiative pion photoproduction γp → γπ+n from the proton at MAMI in Mainz. A stringent test of chiral perturbation theory (ChPT) is possible based on comparisons of precision experimental charged pion polarizabilities with ChPT predictions. Only the CERN COMPASS charged pion polarizability measurement has acceptably small uncertainties. Its value απ±- βπ± = (4.0 ± 1.8) × 10-4fm3 agrees well with the two-loop ChPT prediction απ±- βπ± = (5.7 ± 1.0) × 10-4fm3, strengthening the identification of the pion with the Goldstone boson of chiral symmetry breaking in QCD.
AB - The electric (απ) and magnetic (βπ) Compton polarizabilities of both the charged and the neutral pion are of fundamental interest in the low-energy sector of quantum chromodynamics (QCD). Pion polarizabilities affect the shape of the γπ → γπ Compton scattering angular distribution at back scattering angles and γγ → ππ absolute cross sections. Theory derivations are given for the γπ → γπ Compton scattering differential cross section, dispersion relations, and sum rules in terms of the polarizabilities. We review experimental charged and neutral polarizability studies and theoretical predictions. The π0 polarizabilities were deduced from DESY Crystal Ball γγ → π0π0 data, but with large uncertainties. The charged pion polarizabilities were deduced most recently from (1) radiative pion Primakoff scattering π-Z → π-Zγ at CERN COMPASS, (2) two-photon pion pair production γγ → π+π- at SLAC Mark II, and (3) radiative pion photoproduction γp → γπ+n from the proton at MAMI in Mainz. A stringent test of chiral perturbation theory (ChPT) is possible based on comparisons of precision experimental charged pion polarizabilities with ChPT predictions. Only the CERN COMPASS charged pion polarizability measurement has acceptably small uncertainties. Its value απ±- βπ± = (4.0 ± 1.8) × 10-4fm3 agrees well with the two-loop ChPT prediction απ±- βπ± = (5.7 ± 1.0) × 10-4fm3, strengthening the identification of the pion with the Goldstone boson of chiral symmetry breaking in QCD.
KW - Pion electric and magnetic polarizabilities
KW - charged pion
KW - chiral perturbation theory
KW - chiral symmetry
KW - dispersion relations
KW - experimental tests
KW - neutral pion
KW - pion Compton scattering
KW - pion generalized dipole polarizabilities
KW - pion virtual Compton scattering
KW - pion-nucleus bremsstrahlung
KW - two-photon pion pair production
KW - virtual photon
UR - http://www.scopus.com/inward/record.url?scp=85067188510&partnerID=8YFLogxK
U2 - 10.1142/S0217751X19300084
DO - 10.1142/S0217751X19300084
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AN - SCOPUS:85067188510
SN - 0217-751X
VL - 34
JO - International Journal of Modern Physics A
JF - International Journal of Modern Physics A
IS - 16
M1 - 1930008
ER -