Lattice QCD and Three-Particle Decays of Resonances
21 Oct 2019-Annual Review of Nuclear and Particle Science (Annual Reviews)-Vol. 69, Iss: 1, pp 65-107
TL;DR: Most strong interaction resonances have decay channels involving three or more particles, including many of the recently discovered X, Y, and Z resonances as mentioned in this paper, and in order to study such resonances from finite-state models, we need to study the decay channels of these resonances.
Abstract: Most strong-interaction resonances have decay channels involving three or more particles, including many of the recently discovered X, Y, and Z resonances. In order to study such resonances from fi...
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Technische Universität München1, Ludwig Maximilian University of Munich2, Russian Academy of Sciences3, Novosibirsk State University4, Budker Institute of Nuclear Physics5, Forschungszentrum Jülich6, Moscow Institute of Physics and Technology7, National Research Nuclear University MEPhI8, Fudan University9, Beihang University10, University of Cambridge11, Chinese Academy of Sciences12
TL;DR: A review of the progress in the field of exotic $XYZ$ hadrons can be found in this article, with a summary on future prospects and challenges, as well as a survey of the current state-of-the-art.
Abstract: The quark model was formulated in 1964 to classify mesons as bound states made of a quark-antiquark pair, and baryons as bound states made of three quarks. For a long time all known mesons and baryons could be classified within this scheme. Quantum Chromodynamics (QCD), however, in principle also allows the existence of more complex structures, generically called exotic hadrons or simply exotics. These include four-quark hadrons (tetraquarks and hadronic molecules), five-quark hadrons (pentaquarks) and states with active gluonic degrees of freedom (hybrids), and even states of pure glue (glueballs). Exotic hadrons have been systematically searched for in numerous experiments for many years. Remarkably, in the past fifteen years, many new hadrons that do not exhibit the expected properties of ordinary (not exotic) hadrons have been discovered in the quarkonium spectrum. These hadrons are collectively known as $XYZ$ states. Some of them, like the charged states, are undoubtedly exotic. Parallel to the experimental progress, the last decades have also witnessed an enormous theoretical effort to reach a theoretical understanding of the $XYZ$ states. Theoretical approaches include not only phenomenological extensions of the quark model to exotics, but also modern non-relativistic effective field theories and lattice QCD calculations. The present work aims at reviewing the rapid progress in the field of exotic $XYZ$ hadrons over the past few years both in experiments and theory. It concludes with a summary on future prospects and challenges.
298 citations
Technische Universität München1, Ludwig Maximilian University of Munich2, Budker Institute of Nuclear Physics3, Russian Academy of Sciences4, Novosibirsk State University5, Forschungszentrum Jülich6, Moscow Institute of Physics and Technology7, National Research Nuclear University MEPhI8, Fudan University9, Beihang University10, University of Cambridge11, Chinese Academy of Sciences12
TL;DR: A review of the progress in the field of exotic X Y Y Z hadrons can be found in this paper, where the authors present a summary of the future prospects and challenges.
207 citations
TL;DR: The spectrum of two- and three-pion states of maximal isospin obtained recently for isosymmetric QCD with pion mass M≈200 MeV in Hörz and Hanlon is analyzed and ∼2σ evidence for a nonzero value for the contact part of the 3π^{+} (I=3) scattering amplitude is found.
Abstract: We analyze the spectrum of two- and three-pion states of maximal isospin obtained recently for isosymmetric QCD with pion mass M≈200 MeV in Horz and Hanlon, [Phys. Rev. Lett. 123, 142002 (2019)PRLTAO0031-900710.1103/PhysRevLett.123.142002]. Using the relativistic three-particle quantization condition, we find ∼2σ evidence for a nonzero value for the contact part of the 3π^{+} (I=3) scattering amplitude. We also compare our results to leading-order chiral perturbation theory. We find good agreement at threshold and some tension in the energy dependent part of the 3π^{+} scattering amplitude. We also find that the 2π^{+} (I=2) spectrum is fit well by an s-wave phase shift that incorporates the expected Adler zero.
86 citations
TL;DR: In this article, a formalism for three-body systems in moving frames was developed and applied numerically to obtain the three-S$-matrix principle of unitarity.
Abstract: Strong three-body interactions above threshold govern the dynamics of many exotics and conventional excited mesons and baryons. Three-body finite-volume energies calculated from lattice QCD promise an ab initio understanding of these systems. We calculate the three-${\ensuremath{\pi}}^{+}$ spectrum unraveling the three-body dynamics that is tightly intertwined with the $S$-matrix principle of three-body unitarity and compare it with recent lattice QCD results. For this purpose, we develop a formalism for three-body systems in moving frames and apply it numerically.
69 citations
TL;DR: In this article, the authors show that lattice QCD calculations have reached a stage where these three-body states can be accurately resolved, using three positively charged pions, with different lattice geometries and quark masses, and find all states below inelastic threshold agree with predictions from a state-of-theart phenomenological formalism.
Abstract: Three-body states are critical to the dynamics of many hadronic resonances. We show that lattice QCD calculations have reached a stage where these states can be accurately resolved. We perform a calculation over a wide range of parameters and find all states below inelastic threshold agree with predictions from a state-of-the-art phenomenological formalism. This also illustrates the reliability of the formalism used to connect lattice QCD results to infinite volume physics. Our calculation is performed using three positively charged pions, with different lattice geometries and quark masses.
69 citations