Persona: Fernández Ramírez, César
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Fernández Ramírez
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Publicación Dispersive analysis of 𝜔/𝜙→3𝜋,𝜋𝛾*(American Physical Society, 2015-05-27) Danilkin, J. V.; Fernández Ramírez, César; Guo, P.; Mathieu, V.; Schott, D.; Shi, M.; Szczepaniak, P.The decays 𝜔/𝜙 →3𝜋 are considered in the dispersive framework that is based on the isobar decomposition and subenergy unitarity. The inelastic contributions are parametrized by the power series in a suitably chosen conformal variable that properly accounts for the analytic properties of the amplitude. The Dalitz plot distributions and integrated decay widths are presented. Our results indicate that the final-state interactions may be sizable. As a further application of the formalism we also compute the electromagnetic transition form factors of 𝜔/𝜙 →𝜋0𝛾*.Publicación Determination of the Pole Position of the Lightest Hybrid Meson Candidate(American Physical Society, 2019-01-29) Rodas, A.; Albadalejo, M.; Jackura, A.; Fernández Ramírez, César; Mathieu, V.; Mikhasenko, M.; Nys, J.; Pauk, V.; Ketzer, B.; Szczepaniak, A.P.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, 𝜋1(1400) and 𝜋1(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 𝜋1 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 𝑎2(1320) and 𝑎′ 2(1700).Publicación Equivalence of three-particle scattering formalisms(American Physical Society, 2019-08-13) Jackura, A. W.; Dawid, S. M.; Fernández Ramírez, César; Mathieu, V.; Mikhasenko, M.; Pilloni, A.; Sharpe, S. R.; Szczepaniak, A. P.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.Publicación Interpretation of the LHCb 𝑃𝑐(4312)+ Signal(American Physical Society, 2019-08-29) Fernández Ramírez, César; Pilloni, A; Albadalejo, M.; Jackura, A.; Mathieu, V.; Mikhasenko, M.; Silva castro, J.A.; Szczepaniak, A.P.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 Σ+𝑐¯𝐷0 channel, which is not strong enough, however, to form a bound state.Publicación Regge phenomenology of the 𝑁* and Δ* poles(American Physical Society, 2019-01-13) Silva castro, J.A.; Fernández Ramírez, César; Albaladejo, M.; Danilkin, I.V.; Jackura, A.; Mathieu, V.; Nys, J.; Pilloni, A.; Szczepaniak, A.P.We use Regge phenomenology to study the structure of the poles of the 𝑁* and Δ* spectrum. We employ the available pole extractions from partial wave analysis of meson scattering and photoproduction data. We assess the importance of the imaginary part of the poles (widths) to obtain a consistent determination of the parameters of the Regge trajectory. We compare the several pole extractions and show how Regge phenomenology can be used to gain insight into the internal structure of baryons. We find that the majority of the states in the parent Regge trajectories are compatible with a mostly compact three-quark state picture.