Mapping states with explicit gluonic degrees of freedom in the light sector is a challenge, and has led to controversies in the past. In particular, the experiments have reported two different hybrid ...candidates with spin-exotic signature, π_{1}(1400) and π_{1}(1600), which couple separately to ηπ and η^{'}π. This picture is not compatible with recent Lattice QCD estimates for hybrid states, nor with most phenomenological models. We consider the recent partial wave analysis of the η^{(')}π system by the COMPASS Collaboration. We fit the extracted intensities and phases with a coupled-channel amplitude that enforces the unitarity and analyticity of the S matrix. We provide a robust extraction of a single exotic π_{1} resonant pole, with mass and width 1564±24±86 and 492±54±102 MeV, which couples to both η^{(')}π channels. We find no evidence for a second exotic state. We also provide the resonance parameters of the a_{2}(1320) and a_{2}^{'}(1700).
We study the nature of the new signal reported by LHCb in the J/ψp spectrum. Based on the S-matrix principles, we perform a minimum-bias analysis of the underlying reaction amplitude, focusing on the ...analytic properties that can be related to the microscopic origin of the Pc(4312)+ peak. By exploring several amplitude parametrizations, we find evidence for the attractive effect of the Σc+D¯0 channel, which is not strong enough, however, to form a bound state.
Three-body scattering: ladders and resonances Mikhasenko, M.; Wunderlich, Y.; Jackura, A. ...
The journal of high energy physics,
08/2019, Letnik:
2019, Številka:
8
Journal Article
Recenzirano
Odprti dostop
A
bstract
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.
The microscopic nature of the XYZ states remains an unsettled topic. We show how a thorough amplitude analysis of the data can help constraining models of these states. Specifically, we consider the ...case of the Zc(3900) peak and discuss possible scenarios of a QCD state, virtual state, or a kinematical enhancement. We conclude that current data are not precise enough to distinguish between these hypotheses, however, the method we propose, when applied to the forthcoming high-statistics measurements should shed light on the nature of these exotic enhancements.
In recent years, different on-shell 3→3 scattering formalisms have been proposed to be applied to both lattice QCD and infinite-volume scattering processes. We prove that the formulation in the ...infinite volume presented by Hansen and Sharpe in M. T. Hansen and S. R. Sharpe, Phys. Rev. D 92, 114509 (2015). and subsequently Briceño et al. in R. A. Briceño, M. T. Hansen, and S. R. Sharpe, Phys. Rev. D 95, 074510 (2017). can be recovered from the B-matrix representation, derived on the basis of S-matrix unitarity, presented by Mai et al. in M. Mai, B. Hu, M. Döring, A. Pilloni, and A. Szczepaniak, Eur. Phys. J. A 53, 177 (2017). and Jackura et al. in A. Jackura, C. Fernández-Ramírez, V. Mathieu, M. Mikhasenko, J. Nys, A. Pilloni, K. Saldaña, N. Sherrill, and A. P. Szczepaniak (JPAC Collaboration), Eur. Phys. J. C 79, 56 (2019). Therefore, both formalisms in the infinite volume are equivalent and the physical content is identical. Additionally, the Faddeev equations are recovered in the nonrelativistic limit of both representations.
We study the nature of the new signal reported by LHCb in the $J/Ψp$ spectrum. Based on the S-matrix principles, we perform a minimum-bias analysis of the underlying reaction amplitude, focusing on ...the analytic properties that can be related to the microscopic origin of the $P_c$(4312)+ peak. By exploring several amplitude parameterizations, we find evidence for the attractive effect of the $Σ^+_c$$\bar{D}^0$ channel, that is not strong enough, however, to form a bound state.
We perform an analysis of the three-pion system with quantum numbers JPC=1++ produced in the weak decay of τ leptons. The interaction is known to be dominated by the axial meson a1(1260). We build a ...model based on approximate three-body unitary and fix the free parameters by fitting it to the ALEPH data on τ−→π−π+π−ντ decay. We then perform the analytic continuation of the amplitude to the complex energy plane. The singularity structures related to the ππ subchannel resonances are carefully addressed. Finally, we extract the a1(1260) pole position mp(a1(1260))−iΓp(a1(1260))/2 with mp(a1(1260))=(1209±4−9+12) MeV, Γp(a1(1260))=(576±11−20+89) MeV.
In the search for exotic mesons, the GlueX Collaboration will soon extract moments of the ηπ0 angular distribution. In the perspective of these results, we generalize the formalism of moment ...extraction to the case in which the two mesons are produced with a linearly polarized beam and build a model for the reaction γ→p→ηπ0p. The model includes resonant S, P, and D waves in ηπ0, produced by natural exchanges. Moments of the ηπ0 angular distribution are computed with and without the P wave, to illustrate the sensitivity to exotic resonances. Although little sensitivity to the P wave is found in moments of even angular momentum, moments of odd angular momentum are proportional to the interference between the P wave and the dominant S and D waves. We also generalize the definition of the beam asymmetry for two mesons photoproduction and show that, when the meson momenta are perpendicular to the reaction plane, the beam asymmetry enhances the sensitivity to the exotic P wave.
The microscopic nature of the XYZ states remains an unsettled topic. We show how a thorough amplitude analysis of the data can help constraining models of these states. Specifically, we consider the ...case of the Zc(3900) peak and discuss possible scenarios of a QCD state, virtual state, or a kinematical enhancement. Here, we conclude that current data are not precise enough to distinguish between these hypotheses, however, the method we propose, when applied to the forthcoming high-statistics measurements should shed light on the nature of these exotic enhancements.
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, which 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 line shapes 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 Λc+→pK−π+ decay.
PDF
