content_image/343150.jpg content_image/343151.jpg
to remind the nice mass spectra obtained with help of the phenomenological mass relation [39] obtained within the assumption of two clusters of quarks at the ends of a stretched bag in terms of color magnetic interactions: 

<img src='content_image/343150.jpg'>

<img src='content_image/343151.jpg'>

Here i and s are isospins and spins of the two clusters. Notice that the formula involves degeneracy. We adjust the two parameters M 0 =838.2 MeV and M 1 =100.3 MeV in order to reproduce the masses, spins and isospins of the nucleon and of the Roper resonnace: N ∗ (1440). Then we calculate the masses of the other structures without any free parameter. These masses, possible spins and isospins, quark configurations, and parities if only s wave are considered, are shown in Fig. 27. Notice that the parity of the Roper N ∗ (1440) is positive if a P wave between ( qqq ) and q ¯ q ) quark clusters is assumed. 

