Measurement of radiative widths of $a_2(1320)$ and ${\pi }_2(1670)$

Abstract

The COMPASS Collaboration at CERN has investigated the reaction ${\pi }^{-}\gamma \to {\pi }^{-}{\pi }^{-}{\pi }^{+}$ embedded in the Primakoff reaction of $190\text{GeV}$ pions scattering in the Coulomb field of a lead target, ${\pi }^{-}\text{Pb}\to {\pi }^{-}{\pi }^{-}{\pi }^{+}\text{Pb}$. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at momentum transfer below $0.001(\text{GeV}/c{)}^2$. Using a partial-wave analysis the amplitudes and relative phases of the $a_2(1320)$ and ${\pi }_2(1670)$ mesons have been extracted, and the Coulomb and the diffractive contributions have been disentangled. Measuring absolute production cross sections we have determined the radiative width of the $a_2(1320)$ to be ${\Gamma }_0(a_2(1320)\to \pi \gamma )=(358\pm 6_{\text{stat}}\pm 42_{\text{syst}})\text{keV}$. As the first measurement, ${\Gamma }_0({\pi }_2(1670)\to \pi \gamma )=(181\pm 11_{\text{stat}}\pm 27_{\text{syst}})\text{keV}\cdot ({\text{BR}}_{f_2\pi }^{\text{PDG}}/{\text{BR}}_{f_2\pi })$ is obtained for the radiative width of the ${\pi }_2(1670)$, where in this analysis the branching ratio ${\text{BR}}_{f_2\pi }^{\text{PDG}}=0.56$ has been used. We compare these values to previous measurements and theoretical predictions.

arXiv comment27 pages, 12 figures and 3 tables

References in corpus (8)

• The COMPASS Experiment at CERN
• Cross sections for low-energy ${\pi }^{-}\gamma$ reactions
• Covariant Helicity-Coupling Amplitudes: A New Formulation
• First Measurement of Chiral Dynamics in π^- γ-> π^- π^- π^+
• Chiral corrections to ${\pi }^{-}\gamma \to 3\pi$ processes at low energies
• Radiative decay width of the a2(1320)^- meson
• Coulomb-nuclear interference in pion-nucleus bremsstrahlung
• A remark on the Primakoff effect

Cited by in corpus (7)

• Light isovector resonances in ${\pi }^{-}p\to {\pi }^{-}{\pi }^{-}{\pi }^{+}p$ at 190 GeV/$c$
• Radiative resonance couplings in $\gamma \pi \to \pi \pi$
• Light-Meson Spectroscopy with COMPASS
• Resonance Production and $\pi \pi$ S-wave in ${\pi }^{-}+p\to {\pi }^{-}{\pi }^{-}{\pi }^{+}+p_{recoil}$ at 190 GeV/c
• Dispersive analysis of the Primakoff reaction $\gamma K\to K\pi$
• Polarizabilities from kaon Compton scattering
• Highlights from the COMPASS experiment at CERN -- Hadron spectroscopy and excitations