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The "a₁(1420)" peak as the π f₀(980) decay mode of the a₁(1260)
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The "a₁(1420)" peak as the π f₀(980) decay mode of the a₁(1260)
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We study the decay mode of the $a_1(1260)$ into a $\pi^+$ in p-wave and the $f_0(980)$ that decays into $\pi^+ \pi^-$ in s-wave. The mechanisms proceeds via a triangular mechanism where the $a_1(1260)$ decays into $K^* \bar K$, the $K^*$ decays to an external $\pi^+$ and an internal $K$ that fuses with the $\bar K$ to produce the $f_0(980)$ resonance. The mechanism develops a singularity at a mass of the $a_1(1260)$ around 1420 MeV, producing a peak in the cross section of the $\pi p$ reaction, used to generate the mesonic final state, which provides a natural explanation of all the features observed in the COMPASS experiment, where a peak observed at this energy is tentatively associated to a new resonance called $a_1(1420)$. On the other hand, the triangular singularity studied here gives rise to a remarkable feature, where a peak is seen for a certain decay channel of a resonance at an energy about 200 MeV higher than its nominal mass.
Forward citations
Cited by 4 Pith papers
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The $a_1(1420)$ in a Unitary Coupled-Channel Three-Body Approach
Nine-channel unitary three-body fits to COMPASS lineshapes reproduce the a1(1420) enhancement by triangle singularity without requiring a genuine a1(1420) pole.
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Three-body unitary determination of the $f_1(1285)$ and $f_1(1420)$ pole positions
Fitting a spectator-isobar three-body unitary amplitude to BESIII K0S K0S pi0 data yields poles at (1277±2±1)-i(12±1±0) MeV for f1(1285) and (1435±2±7)-i(40±2±1) MeV for f1(1420), with the latter traced to a K Kbar* q...
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The $a_1(1420)$ in a Unitary Coupled-Channel Three-Body Approach
Unitary coupled-channel three-body model fitted to COMPASS data reproduces the a1(1420) enhancement via triangle singularity, indicating no genuine resonance pole is required.
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Effects of Final State Interactions on Landau Singularities
Triangle singularities mimicking resonances are analyzed in the presence of final-state rescattering using Landau equations and a scattering formalism enforcing two- and three-body unitarity.
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