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
30m
Hotel do Bosque

#### Hotel do Bosque

Oral presentation Hadronic structure - reactions, production and decays

### Speaker

Dr Gilberto Ramalho (UFRN)

### Description

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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