C. Fernández-Ramírez

Thomas Jefferson National Accelerator Facility, Ньюпорт-Ньюс, Virginia, United States

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Publications (28)93.34 Total impact

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    ABSTRACT: We compare the low-energy partial wave analyses $\pi N$ scattering with a high-energy data via finite energy sum rules. We construct a new set of amplitudes by matching the imaginary part from the low-energy analysis with the high-energy, Regge parametrization and reconstruct the real parts using dispersion relations.
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    ABSTRACT: New results are reported from a measurement of π^{0} electroproduction near threshold using the p(e,e^{'}p)π^{0} reaction. The experiment was designed to determine precisely the energy dependence of s- and p-wave electromagnetic multipoles as a stringent test of the predictions of chiral perturbation theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the ϕ_{π}^{*} and θ_{π}^{*} angles in the pπ^{0} center of mass was obtained for invariant energies above threshold from 0.5 up to 15 MeV. The 4-momentum transfer Q^{2} coverage ranges from 0.05 to 0.155 (GeV/c)^{2} in fine steps. A simple phenomenological analysis of our data shows strong disagreement with p-wave predictions from ChPT for Q^{2}>0.07 (GeV/c)^{2}, while the s-wave predictions are in reasonable agreement.
    Physical Review Letters 05/2015; 114(19):192503. · 7.73 Impact Factor
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    ABSTRACT: We present an unitary dispersive model for the $\eta \to 3 \pi$ decay process based upon the Khuri-Treiman equations which are solved by means of the Pasquier inversion method. The description of the hadronic final-state interactions for the $\eta \to 3\pi$ decay is essential to reproduce the available data and to understand the existing discrepancies between Dalitz plot parameters from experiment and chiral perturbation theory. Our approach incorporates substraction constants that are fixed by fitting the recent high-statistics WASA-at-COSY data for $\eta \to \pi^+ \pi^- \pi^0$. Based on the parameters obtained we predict the slope parameter for the neutral channel to be $\alpha=-0.022\pm 0.004$. Through matching to next-to-leading order chiral perturbation theory we estimate the quark mass double ratio to be $Q=21.4 \pm 0.4$.
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    ABSTRACT: New results are reported from an experiment to measure $\pi^0$ electroproduction at and above threshold using the $p(e,e^{\prime} p)\pi^0$ reaction. The experiment was designed to precisely determine the energy dependence of $s-$ and $p-$wave electromagnetic multipoles as a stringent test of the predictions of Chiral Perturbation Theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the $\phi^*_{\pi}$ and $\theta^*_{\pi}$ angles in the $p \pi^0$ center-of-mass was obtained for invariant energies above threshold from 0.5~MeV up to 15~MeV. The 4-momentum transfer $Q^2$ coverage ranges from 0.05 to 0.155 (GeV/c)$^2$ in fine steps. A simple phenomenological analysis of our data shows strong disagreement with $p-$wave predictions from ChPT for $Q^2>0.07$ (GeV/c)$^2$, while the $s-$wave predictions are in reasonable agreement.
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    ABSTRACT: We apply the generalized Veneziano model ($B_5$ model) in the double-Regge exchange limit to the $\gamma p \to K^+ K^- p$ reaction. Four different cases defined by the possible combinations of the signature factors of leading Regge exchanges (($K^*,a_2/f_2$), ($K^*,\rho/\omega$), ($K_2^*,a_2/f_2$), and ($K_2^*,\rho/\omega$)) have been simulated through the Monte Carlo method. Suitable event candidates for the double-Regge exchange high-energy limit were selected employing \textit{Van Hove} plots as a better alternative to kinematical cuts in the $K^+ K^- p$ Dalitz plot. In this way we predict and analyze the double-Regge contribution to the $K^+ K^- p$ Dalitz plot, which constitutes one of the major backgrounds in the search for strangeonia, hybrids and exotics using $\gamma p\rightarrow K^+K^-p$ reaction. We expect that data currently under analysis, and that to come in the future, will allow verification of the double-Regge behavior and a better assessment of this component of the amplitude.
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    ABSTRACT: The decays $\omega/\phi \rightarrow 3\pi$ are considered in the dispersive framework that is based on the isobar decomposition and sub-energy unitarity. The inelastic contributions are parametrized by the power series in a suitably chosen conformal variable that properly account 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 $\omega/\phi \rightarrow \pi^0\gamma^*$.
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    ABSTRACT: A precision measurement of the differential cross sections dσ/dΩ and the linearly polarized photon asymmetry Σ≡(dσ_{⊥}-dσ_{∥})/(dσ_{⊥}+dσ_{∥}) for the γ[over →]p→π^{0}p reaction in the near-threshold region has been performed with a tagged photon beam and almost 4π detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multiphoton detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the S- and all three P-wave amplitudes for the first time and provide the most stringent test to date of the predictions of chiral perturbation theory and its energy region of agreement with experiment.
    Physical Review Letters 08/2013; 111(6):062004. · 7.73 Impact Factor
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    ABSTRACT: The mini-proceedings of the Workshop on PWA tools in Hadronic Spectroscopy held in Mainz from February 18th to 20th, 2013.
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    C. Fernandez-Ramirez, A. M. Bernstein
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    ABSTRACT: With the availability of the new neutral pion photoproduction from the proton data from the A2 and CB-TAPS Collaborations at Mainz it is mandatory to revisit Heavy Baryon Chiral Perturbation Theory (HBChPT) and address the extraction of the partial waves as well as other issues such as the value of the low-energy constants, the energy range where the calculation provides a good agreement with the data and the impact of unitarity. We find that, within the current experimental status, HBChPT with the fitted LECs gives a good agreement with the existing neutral pion photoproduction data up to $\sim$170 MeV and that imposing unitarity does not improve this picture. Above this energy the data call for further improvement in the theory such as the explicit inclusion of the \Delta (1232). We also find that data and multipoles can be well described up to $\sim$185 MeV with Taylor expansions in the partial waves up to first order in pion energy.
    Physics Letters B 12/2012; 724(4-5). DOI:10.1016/j.physletb.2013.06.020 · 6.02 Impact Factor
  • C. Fernández-Ramírez, L. Muñoz, A. Relaño, J. Retamosa
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    ABSTRACT: Quantum chaos is currently a well established discipline with outreach to many fields of physics. The most important signature of quantum chaos is the statistical analysis of the energy spectrum, which distinguishes between systems with integrable and chaotic classical analogues. The spectral statistical techniques inherited from quantum chaos have been applied to the baryon spectrum revealing its likely chaotic behavior in the low energy regime [1,2]. We present a robust analysis of the spectral fluctuations exhibited by the light meson spectrum. With this analysis we can obtain information about the degree of chaos in the spectrum getting insight on the properties of the underlying interactions. Our analysis unveils that the statistical properties of the light meson spectrum are close, but not exactly equal, to those of chaotic systems [3]. Besides the experimental spectrum, we have analyzed several theoretical spectra [4-7] including the latest lattice QCD calculation [8] finding out that, with the single exception of [5], their statistical properties are close to those of a generic integrable system, and thus incompatible with the experimental result.
    The European Physical Journal Conferences 12/2012; 37:04001-. DOI:10.1051/epjconf/20123704001
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    ABSTRACT: A precision measurement of the differential cross sections $d\sigma/d\Omega$ and the linearly polarized photon asymmetry $\Sigma \equiv (d\sigma_\perp - d\sigma_\parallel) \slash (d\sigma_\perp + d\sigma_\parallel)$ for the $\vec{\gamma} p \rightarrow \pi^0p$ reaction in the near-threshold region has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multi-photon detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$- and all three $P$-wave amplitudes for the first time and provide the most stringent test to date of the predictions of Chiral Perturbation Theory and its energy region of agreement with experiment.
    Physical Review Letters 11/2012; 111(062004). DOI:10.1103/PhysRevLett.111.062004 · 7.73 Impact Factor
  • L. Muñoz, C. Fernández-Ramírez, A. Relaño, J. Retamosa
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    ABSTRACT: In the last decade quantum chaos has become a well established discipline with outreach to different fields, from condensed-matter to nuclear physics. The most important signature of quantum chaos is the statistical analysis of the energy spectrum, which distinguishes between systems with integrable and chaotic classical analogues. In recent years, spectral statistical techniques inherited from quantum chaos have been applied successfully to the baryon spectrum revealing its likely chaotic behaviour even at the lowest energies. However, the theoretical spectra present a behaviour closer to the statistics of integrable systems which makes theory and experiment statistically incompatible. The usual statement of missing resonances in the experimental spectrum when compared to the theoretical ones cannot account for the discrepancies. In this communication we report an improved analysis of the baryon spectrum, taking into account the low statistics and the error bars associated with each resonance. Our findings give a major support to the previous conclusions. Besides, analogue analyses are performed in the experimental meson spectrum, with comparison to theoretical models.
    Journal of Physics Conference Series 09/2012; 381(1):2031-. DOI:10.1088/1742-6596/381/1/012031
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    L. Munoz, C. Fernandez-Ramirez, A. Relano, J. Retamosa
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    ABSTRACT: We present a robust analysis of the spectral fluctuations exhibited by the light meson spectrum. This analysis provides information about the degree of chaos in light mesons and may be useful to get some insight on the underlying interactions. Our analysis unveils that the statistical properties of the light meson spectrum are close, but not exactly equal, to those of chaotic systems. In addition, we have analyzed several theoretical spectra including the latest lattice QCD calculation. With a single exception, their statistical properties are close to those of a generic integrable system, and thus incompatible with the experimental spectrum.
    Physics Letters B 03/2012; 710(1). DOI:10.1016/j.physletb.2012.02.050 · 6.02 Impact Factor
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    ABSTRACT: The electric form factor of the neutron was determined from studies of the reaction 3He(e,e'n)pp in quasielastic kinematics in Hall A at Jefferson Lab. Longitudinally polarized electrons were scattered off a polarized target in which the nuclear polarization was oriented perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons that were registered in a large-solid-angle detector. More than doubling the Q2 range over which it is known, we find G(E)(n)=0.0236±0.0017(stat)±0.0026(syst), 0.0208±0.0024±0.0019, and 0.0147±0.0020±0.0014 for Q(2)=1.72, 2.48, and 3.41 GeV2, respectively.
    Physical Review Letters 12/2010; 105(26):262302. DOI:10.1103/PhysRevLett.105.262302 · 7.73 Impact Factor
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    C. Fernandez-Ramirez
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    ABSTRACT: It has been commonly assumed that low-energy neutral pion photoproduction from the proton can be described accounting only for S and P waves, and that higher partial waves are irrelevant. We have found that this assumption is not correct and that the inclusion of D waves is necessary to obtain a reliable extraction of the $E_{0+}$ multipole from experimental data. This is due in large measure to the spontaneous breaking of chiral symmetry in QCD which leads to very small S-wave contributions. This makes the usual partial wave expansion less accurate and although D waves are small, their contribution is enhanced through the interference with P waves, which compromises the S-wave extraction from data if D waves are not taken into account. In our work we have used Heavy Baryon Chiral Perturbation Theory to one loop, and up to ${\cal O}(q^4)$, to account for the S and P waves, while D waves are added in an almost model-independent way using standard Born terms and vector mesons. We also show that higher partial waves do not play an important role. Comment: Talk presented in the 6th International Workshop on Chiral Dynamics, July 6-10 2009, Bern, Switzerland. To be published in Proceedings of Science. Uses class Pos.cls (included). 6 pages and 3 figures
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    C. Fernandez-Ramirez, A. M. Bernstein, T. W. Donnelly
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    ABSTRACT: Contributions of D waves to physical observables for neutral pion photoproduction from the proton in the near-threshold region are studied and means to isolate them are proposed. Various approaches to describe the multipoles are employed--a phenomenological one, a unitary one, and heavy baryon chiral perturbation theory. The results of these approaches are compared and found to yield essentially the same answers. D waves are seen to enter together with S waves in a way that any means which attempt to obtain the E{sub 0+} multipole accurately must rely on knowledge of D waves and that consequently the latter cannot be dismissed in analyses of low-energy pion photoproduction. It is shown that D waves have a significant impact on double-polarization observables that can be measured. This importance of D waves is due to the soft nature of the S wave and is a direct consequence of chiral symmetry and the Nambu-Goldstone nature of the pion. F-wave contributions are shown to be negligible in the near-threshold region.
    Physical Review C 12/2009; 80(6). DOI:10.1103/PHYSREVC.80.065201 · 3.88 Impact Factor
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    C. Fernandez-Ramirez, A. M. Bernstein, T. W. Donnelly
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    ABSTRACT: The contribution of D waves to physical observables for neutral pion photoproduction in the near threshold region is studied. Heavy Baryon Chiral Perturbation Theory to one loop, and up to ${\cal O}(q^4)$, is used to account for the S and P waves, while D waves are added in an almost model-independent way using standard Born terms and vector mesons. It is found that the inclusion of D waves is necessary to extract the $E_{0+}$ multipole reliably from present and forthcoming data and to assess the low-energy constants of Chiral Perturbation Theory. Arguments are presented demonstrating that F-wave contributions are negligible in the near-threshold region. Comment: 10 pages, 5 figures
    Physics Letters B 02/2009; 679(1). DOI:10.1016/j.physletb.2009.07.011 · 6.02 Impact Factor
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    C. Fernandez-Ramirez, E. Moya de Guerra, A. Udias, J. M. Udias
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    ABSTRACT: We present an optimization scheme that employs a Genetic Algorithm (GA) to determine the properties of low-lying nucleon excitations within a realistic photo-pion production model based upon an effective Lagrangian. We show that with this modern optimization technique it is possible to reliably assess the parameters of the resonances and the associated error bars as well as to identify weaknesses in the models. To illustrate the problems the optimization process may encounter, we provide results obtained for the nucleon resonances $\Delta$(1230) and $\Delta$(1700). The former can be easily isolated and thus has been studied in depth, while the latter is not as well known experimentally.
    Physical Review C 06/2008; 78(6):65212. DOI:10.1103/PhysRevC.77.065212 · 3.88 Impact Factor
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    C. Fernández-Ramírez, M.C. Martínez, Javier R. Vignote, J.M. Udías
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    ABSTRACT: The spin asymmetry of the photon in the exclusive reaction is computed employing a recently developed fully relativistic model based on elementary pion production amplitudes that include a consistent treatment of the spin-3/2 nucleon resonances. We compare the results of this model to the only available data on Oxygen [K. Hicks, et al., Phys. Rev. C 61 (2000) 054609] and find that, contrary to other models, the predicted spin asymmetry compares well to the available experimental data in the Δ(1232) region. Our results indicate that no major medium modifications in the Δ(1232) properties are needed in order to describe the measured spin asymmetries.
    Physics Letters B 06/2008; 664(1-2-664):57-63. DOI:10.1016/j.physletb.2008.05.003 · 6.02 Impact Factor
  • E. M. Darwish, C. Fernández-Ramírez, E. Moya de Guerra, J. M. Udías
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    ABSTRACT: Recent results are presented for quasifree pion photoproduction off the deuteron in the energy region from threshold up to the Delta(1232)-resonance with inclusion of all leading piNN effects. Final-state interaction effects are investigated and their role in polarized and unpolarized observables are found to be significant. The sensitivity of results to the elementary N(gamma,pi)N operator is discussed and considerable dependence is found. We expect that these results may be useful to interpret the recent measurements from LEGS, A2 and GDH Collaborations.
    04/2008; 1006(1). DOI:10.1063/1.2927607

Publication Stats

134 Citations
93.34 Total Impact Points

Institutions

  • 2014–2015
    • Thomas Jefferson National Accelerator Facility
      • • Division of Physics
      • • Theoretical and Computational Physics Center
      Ньюпорт-Ньюс, Virginia, United States
  • 2012
    • European Centre for Theoretical Studies in Nuclear Physics and Related Areas
      Trient, Trentino-Alto Adige, Italy
  • 2008–2012
    • Complutense University of Madrid
      • Department of Atomic, Molecular and Nuclear Physics
      Madrid, Madrid, Spain
  • 2008–2009
    • Massachusetts Institute of Technology
      • Center for Theoretical Physics
      Cambridge, MA, United States
  • 2007
    • Universidad de Sevilla
      • Atomic, Molecular and Nuclear Physics
      Hispalis, Andalusia, Spain
    • Instituto de Estructura de la Materia
      Madrid, Madrid, Spain
  • 2005–2006
    • Spanish National Research Council
      • Institute for the Structure of Matter
      Madrid, Madrid, Spain