Beyond the isobar model: Rescattering in the system of three particles.

Mikhasenko, M.; Ketzer, B.

doi:10.22323/1.272.0024

Cited by 3 publications

(2 citation statements)

References 18 publications

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“…The system of three pions also requires a consistent isospin treatment. An extension of this work to the coupled-channel problem is needed for further investigation of the 3π − KKπ coupled system suggested to be responsible for the exotic candidate a 1 (1420) [6,15,66]. We have left aside the problem of time-reversal symmetry violations in KT, which needs to be addressed in the practical cases.…”

Section: Discussionmentioning

confidence: 99%

Three-body scattering: ladders and resonances

Mikhasenko

Wunderlich

Jackura

et al. 2019

J. High Energ. Phys.

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We discuss unitarity constraints on the dynamics of a system of three interacting particles. We show how the short-range interaction that describes three-body resonances can be separated from the long-range exchange processes, in particular the one-pion-exchange process. It is demonstrated that unitarity demands a specific functional form of the amplitude with a clear interpretation: the bare three-particle resonances are dressed by the initial-and final-state interaction, in a way that is consistent with the considered long-range forces. We postulate that the resonance kernel admits a factorization in the energy variables of the initial-and the final-state particles. The factorization assumption leads to an algebraic form for the unitarity equations, which is reminiscent of the well-known two-body-unitarity condition and approaches it in the limit of the narrow-resonance approximation.

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Section: Discussionmentioning

confidence: 99%

Three-body scattering: ladders and resonances

Mikhasenko

Wunderlich

Jackura

et al. 2019

J. High Energ. Phys.

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“…A general framework for a systematic analysis of diffractive meson production at COMPASS using reaction models based on the principles of the relativistic S-matrix is currently under development in collaboration with the Joint Physics Analysis Center (JPAC) [176][177][178][179]. The goal is to extend the Breit-Wigner based fit models discussed in Section 5.3 to analytic models constrained by unitarity, which allows the extraction of resonance pole positions.…”

Section: Analytical Unitary Modelmentioning

confidence: 99%

Light-Meson Spectroscopy with COMPASS

Ketzer,

Grube,

Ryabchikov

2019

Preprint

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Despite decades of research, we still lack a detailed quantitative understanding of the way quantum chromodynamics (QCD) generates the spectrum of hadrons. Precise experimental studies of the hadron excitation spectrum and the dynamics of hadrons help to improve models and to test effective theories and lattice QCD simulations. In addition, QCD seems to allow hadrons beyond the three-quark and quark-antiquark configurations of the constituent-quark model. These so-called exotic hadrons contain additional constituent (anti)quarks or excited gluonic fields that contribute to the quantum numbers of the hadron. Hadron spectroscopy is currently one of the most active fields of research in hadron physics. The COMPASS experiment at the CERN SPS is studying the excitation spectrum of light mesons, which are composed of up, down, and strange quarks. The excited mesons are produced via the strong interaction, i.e. by Pomeron exchange, by scattering a 190 GeV/c pion beam off proton or nuclear targets. On heavy nuclear targets, in addition the electromagnetic interaction contributes in the form of quasi-real photon exchange at very low four-momentum transfer squared. COMPASS has performed the most comprehensive analyses to date of isovector resonances decaying into ηπ, η π, or π − π − π + final states. In this review, we give a general and pedagogical introduction into scattering theory and the employed partial-wave analysis techniques. We also describe novel methods developed for the high-precision COMPASS data. The COMPASS results are summarized and compared to previous measurements. In addition, we discuss possible signals for exotic mesons and conclude that COMPASS data provide solid evidence for the existence of the manifestly exotic π 1 (1600), which has quantum numbers forbidden for a quark-model state, and of the a 1 (1420), which does not fit into the quark-model spectrum. By isolating the contributions from quasi-real photon exchange, COMPASS has measured the radiative widths of the a 2 (1320) and, for the first time, that of the π 2 (1670) and has tested predictions of chiral perturbation theory for the process π − + γ → π − π − π + .

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Dalitz-plot decomposition for three-body decays

et al. 2020

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We present a general formalism to write the decay amplitude for multibody reactions with explicit separation of the rotational degrees of freedom, which are well controlled by the spin of the decay particle, and dynamic functions on the subchannel invariant masses, which require modeling. Using the three-particle kinematics we demonstrate the proposed factorization, named the Dalitz-plot decomposition. The Wigner rotations, that are subtle factors needed by the isobar modeling in the helicity framework, are simplified with the proposed decomposition. Consequently, we are able to provide them in an explicit form suitable for the general case of arbitrary spins. The only unknown model-dependent factors are the isobar lineshapes that describe the subchannel dynamics. The advantages of the new decomposition are shown through three examples relevant for the recent discovery of the exotic charmonium candidate Zc(4430), the pentaquarks Pc, and the intriguing Λ + c → pK − π + decay. I. INTRODUCTIONPartial-wave decomposition of reaction amplitudes is widely used in the analysis of both fixed target (e.g. COM-PASS, VES, CLAS, GlueX), and collider (e.g. LHCb, BESIII, Belle, BaBar) experiments. It is the most powerful way to account for spin and parity, J P , of various contributions, thus required in quantum number determinations of newly observed resonances. It also provides for the most sensitive way of distinguishing exotic hadrons, including the XY Z states and pentaquark candidates in the heavy quarkonium sector, from usually large contributions by ordinary mesons and baryons. To establish the existence of a resonance in a given partial wave, it is desired to have a representation of the reaction amplitude consistent with the S-matrix principles of unitarity, analyticity and Lorentz invariance. This is nontrivial when dealing with particles with spin, which introduce kinematical singularities and (pseudo)threshold relations between partial waves. Amplitude analysis in the context of the S-matrix constraints has been extensively studied in the past using both covariant [1-3] and noncovariant methods [4][5][6][7]. When several particles with spin are involved, the noncovariant approach is more practical, because spin is universally accounted for through the simple Wigner D-functions. In this paper, we take a step to simplify amplitude construction and discuss a convenient framework which incorporates dynamic subchannel resonances for a multiparticle decay. We present a universal amplitude formula which describes the decay of an arbitrary spin state to three particles, each also with arbitrary spin. Specifically, we write the amplitudes in a factorized form to separate the dependence on the angles that characterize the orientation of the final-state particles (and thus the information about the polarization of the parent particle) from the Dalitz-plot variables that encode the information on the intermediate resonances in the multiparticle final state. We do not focus on details of the two-particle dynamics merely giving ...

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Beyond the isobar model: Rescattering in the system of three particles.

Cited by 3 publications

References 18 publications

Three-body scattering: ladders and resonances

Three-body scattering: ladders and resonances

Light-Meson Spectroscopy with COMPASS

Dalitz-plot decomposition for three-body decays

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