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Combined parametrization of GEn and \(\gamma^{\ast} N \rightarrow \Delta (1232)\) quadrupole form factors

  • G. RamalhoEmail author
Regular Article - Theoretical Physics
  • 15 Downloads

Abstract.

Models based on SU(6) symmetry breaking and large Nc limit provide relations between the pion cloud contributions to the \(\gamma^{\ast} N \rightarrow \Delta (1232)\) quadrupole form factors, electric (GE) and Coulomb (GC), and the neutron electric form factor GEn, suggesting that those form factors are dominated by the same physical processes. Those relations are improved in order to satisfy a fundamental constraint between the electric and Coulomb quadrupole form factors in the long wavelength limit, when the photon three-momentum vanishes (Siegert’s theorem). Inspired by those relations, we study alternative parametrizations for the neutron electric form factor. The parameters of the new form are then determined by a combined fit to the GEn and the \( \gamma^{\ast} N \rightarrow \Delta (1232)\) quadrupole form factor data. We obtain a very good description of the GE and GC data when we combine the pion cloud contributions with small valence quark contributions to the \( \gamma^{\ast} N \rightarrow \Delta (1232)\) quadrupole form factors. The best description of the data is obtained when the second momentum of GEn is \( r_{n}^{4} \simeq -0.4\) fm4. We conclude that the square radii associated with GE and GC, \( r_{E}^{2}\) and \( r_{C}^{2}\), respectively, are large, revealing the long extension of the pion cloud. We conclude also that those square radii are related by \( r_{E}^{2} - r_{C}^{2} = 0.6 \pm 0.2\) fm2. The last result is mainly the consequence of the pion cloud effects and Siegert’s theorem.

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Copyright information

© Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Laboratório de Física Teórica e Computacional - LFTCUniversidade Cruzeiro do SulSão PauloBrazil

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