22-27 March 2015
Hotel do Bosque
Brazil/East timezone

A covariant model for the negative parity resonances of the nucleon

23 Mar 2015, 18:30
Hotel do Bosque

Hotel do Bosque

Oral presentation Hadronic structure - reactions, production and decays Hadronic structure - reactions, production and decays


Dr Gilberto Ramalho (UFRN)


One of the challenges of the modern physics is the description of the internal structure of the baryons and mesons. The electromagnetic structure of the nucleon $N$ and the nucleon resonances $N^\ast$ can be accessed through the $\gamma^\ast N \to N^\ast$ reactions, which deppend of the (photon) transfer momentum squared $Q^2$ [1--4]. The data associated with those transitions are represented in terms of helicity amplitudes and have been collected in the recent years at Jefferson Lab, with increasing $Q^2$. The new data demands the development of theoretical models based in the underlying structure of quarks and mesons states [3,4]. Those models can be also very useful to predict the results of the future Jlab--12 GeV upgrade, particularly for resonances in the second and third resonance region (energy $W =1400$--$1750$ GeV) [4]. In that region there are several resonances $N^\ast$ from the supermultiplet $[70,1^-]$ of $SU(6)\otimes O(3)$, characterized by a negative parity [5]. According with the single quark transition model, when the electromagnetic interaction is the result of the photon coupling with just one quark, the helicity amplitudes of the $[70,1^-]$ members depend only of three independent functions of $Q^2$: $A,B$ and $C$ [5,6]. In this work we use the covariant spectator quark model [4,6,7] developed for the $\gamma^\ast N \to N^\ast (1520)$ and $\gamma^\ast N \to N^\ast (1535)$ transitions [8], also members of $[70,1^-]$, to calculate those functions. With the knowledge of the functions $A,B$, and $C$ we predict the helicity amplitudes for the transitions $\gamma^\ast N \to N^\ast(1650)$, $\gamma^\ast N \to N^\ast(1700)$, $\gamma^\ast N \to \Delta(1620)$, and $\gamma^\ast N \to \Delta(1700)$ [6]. To facilitate the comparison with future experimental data at high $Q^2$, we provide also simple parametrizations of the amplitudes $A_{1/2}$ and $A_{3/2}$ for the different transitions, compatible with the expected falloff at high $Q^2$ [6]. [1] I.G. Aznauryan et al. [CLAS Collaboration], Phys. Rev. C 80, 055203 (2009); V.I. Mokeev et al. [CLAS Collaboration], Phys. Rev. C 86, 035203 (2012). [2] L. Tiator, D. Drechsel, S.S. Kamalov and M.Vanderhaeghen, Eur. Phys. J. ST 198, 141 (2011). [3] I.G. Aznauryan and V.D. Burkert, Prog. Part. Nucl. Phys. 67, 1 (2012). [4] I.G. Aznauryan et al. Int. J. Mod. Phys. E 22, 1330015 (2013). [5] V. D. Burkert, R. De Vita, M. Battaglieri, M. Ripani and V. Mokeev, Phys. Rev. C 67, 035204 (2003). [6] G. Ramalho, Phys. Rev. D 90, 033010 (2014). [7] F. Gross, G. Ramalho and M.T.~Peña, Phys. Rev. C 77, 015202 (2008); Phys. Rev. D 85, 093005 (2012). [8] G. Ramalho and M.T. Peña, Phys. Rev. D 89, 094016 (2014); Phys. Rev. D 84, 033007 (2011); G. Ramalho and K. Tsushima, Phys. Rev. D 84, 051301 (2011).

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