Dalitz plot analysis and branching fraction measurement of D+ and D s+ → π −π +π + decays

Abstract

Fermilab fixed target experiment E791 obtained a sample of 1172 ± 61 events of D + → π −π +π + and 848 ±44 events of D s + → π −π +π + decays. We find respectively B( D + → π −π +π +)/ B( D + → K −π +π +) = 0.0311 ± 0.0018 −0.0026 +0.0016 and B( D s + → π +π −π +)/ B( D s + → φπ +) = 0.245 ± 0.028 −0.012 +0.019. Using a coherent amplitude analysis to fit the Dalitz plot of the D + → π −π +π + decay, we find strong evidence for a scalar resonance of mass 478 −23 +24 ± 17 MeV/ c 2 and width 324 −40 +42 ± 21 MeV/ c 2, compatible with what is expected for the isoscalar meson σ. The D + → σ(500)π + fraction accounts for approximately half of all three-charged-pion decays of the D +. From the Dalitz plot analysis of the D s + → π −π +π + decay events, we find significant contributions from the channels ϱ 0(770)π +, ϱ 0(1450)π +, f 0(980)π +, f 2(1270)π +, and f 0(1370)π +. We also present new measurement of the masses and widths of the isoscalar resonances f 0(980) and f 0(1370).