Abstract
We study the spin-exotic JPC=1−+ amplitude in single-diffractive dissociation of 190 GeV/c pions into π−π−π+ using a hydrogen target and confirm the π1(1600)→ρ(770)π amplitude, which interferes with a nonresonant 1−+ amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we thus reconcile these experimental findings. We study the nonresonant contributions to the π−π−π+ final state using pseudodata generated on the basis of a Deck model. Subjecting pseudodata and real data to the same partial-wave analysis, we find good agreement concerning the spectral shape and its dependence on the squared four-momentum transfer for the JPC=1−+ amplitude and also for amplitudes with other JPC quantum numbers. We investigate for the first time the amplitude of the π−π+ subsystem with JPC=1−− in the 3π amplitude with JPC=1−+ employing the novel freed-isobar analysis scheme. We reveal this π−π+ amplitude to be dominated by the ρ(770) for both the π1(1600) and the nonresonant contribution. These findings largely confirm the underlying assumptions for the isobar model used in all previous partial-wave analyses addressing the JPC=1−+ amplitude.7 MoreReceived 6 August 2021Accepted 8 September 2021DOI:https://doi.org/10.1103/PhysRevD.105.012005Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDiffractive productionHadron-hadron interactionsPhysical SystemsExotic mesonsNuclear Physics
Highlights
The presently known meson spectrum is to a large extent attributed to quark-antiquark states
We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we reconcile these experimental findings
We study the nonresonant contributions to the π−π−πþ final state using pseudodata generated on the basis of a Deck model
Summary
While production and decay patterns constitute a mandatory but often strongly model-dependent signature, spin-exotic JPC quantum numbers are generally considered the cleanest path to prove the existence of mesonlike objects beyond qq 0. Three such states with JPC 1⁄4 1−þ, the π1ð1400Þ, π1ð1600Þ, and the π1ð2015Þ, have been discussed frequently as first evidence for exotic mesons and their observation was reported by various experiments [20]. Their masses agree qualitatively with lattice QCD calculations [9].
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