First Measurement of Chiral Dynamics in \pi^- \gamma -> \pi^- \pi^- \pi^+

COMPASS collaboration (212 authors); Bordalo, P.; Franco, C.; Nunes, A.S.; Quintans, C.; Ramos, S.; Silva, L.; Stolarski, M.

http://hdl.handle.net/10400.26/26064

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COMPASS collaboration (212 authors)

Abstract(s)

The COMPASS collaboration at CERN has investigated the \pi^- \gamma -> \pi^- \pi^- \pi^+ reaction at center-of-momentum energy below five pion masses, sqrt(s) < 5 m(\pi), embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, t' < 0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the 3\pi-invariant mass m(3\pi) = sqrt(s) were extracted. The absolute cross section was determined in seven bins of $\sqrt{s}$ with an overall precision of 20%. At leading order, the result is found to be in good agreement with the prediction of chiral perturbation theory over the whole energy range investigated.