Exotic meson <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>1600</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>J</mml:mi><mml:mrow><mml:mi>P</mml:mi><mml:mi>C</mml:mi></mml:mrow></mml:msup><mml:mo>=</mml…

We study the spin-exotic $J^{PC} = 1^{-+}$ amplitude in single-diffractive dissociation of 190 GeV$/c$ pions into $\pi^-\pi^-\pi^+$ using a hydrogen target and confirm $\pi_1(1600) \to \rho(770) \pi$ amplitude, which interferes with nonresonant $1^{-+}$ amplitude. demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models treatment dependence squared four-momentum transfer we thus reconcile their experimental findings. contributions final state pseudo-data generated basis Deck model. Subjecting real data same partial-wave analysis, find good agreement concerning spectral shape its for also other $J^{PC}$ quantum numbers. investigate first time $\pi^-\pi^+$ subsystem 1^{--}$ $3\pi$ employing novel freed-isobar scheme. reveal this dominated by $\rho(770)$ both $\pi_1(1600)$ contribution. determine resonance parameters within three-pion state. These findings largely underlying assumptions isobar model used all analyses addressing