Persona:
Fernández Ramírez, César

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0000-0001-8979-5660
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Fernández Ramírez
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César
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2009 - 200912010 - 20131
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Autor: Bernstein, Aaron M. × search.filters.applied.f.itemFacultad: Facultad de Ciencias ×

Resultados de la búsqueda

Mostrando 1 - 2 de 2
  • Miniatura
    Publicación
    Upper energy limit of heavy baryon chiral perturbation theory in neutral pion photoproduction
    (Elsevier, 2013-07-23) Fernández Ramírez, César; Bernstein, Aaron M.
    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 ∼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 (1232). We also find that data and multipoles can be well described up to ∼185 MeV with Taylor expansions in the partial waves up to first order in pion energy.
  • Miniatura
    Publicación
    Low-energy D-wave effects in neutral pion photoproduction
    (Elsevier, 2009-08-10) Fernández Ramírez, César; Bernstein, Aaron M.; Donnelly, T. W.
    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 O(q4), 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 E0+ 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.