Abstract :
[en] We study the spectrum of the isoscalar pentaquark $udsc\overline{c}$,
of either positive or negative parity,
in a constituent quark model with linear confinement and a flavor-spin hyperfine interaction
previously extended to SU(4) and used to describe the spectrum of the $uudc\overline{c}$ pentaquarks observed at LHCb in 2019.
For positive parity we make a distinction between the case where one unit of angular momentum
is located in the subsystem of four quarks and the case where the angular momentum is located
in the relative motion between a ground state four-quark subsystem and the antiquark.
The novelty is that we introduce the coupling between different
flavor states, due to the breaking of exact SU(4)-flavor symmetry of the Hamiltonian model,
both for positive and negative parity states.
An important consequence is that the lowest state, located at 4404 MeV, has quantum numbers $J^P$ = $1/2^-$
while without coupling the lowest state has $J^P$ = $1/2^+$ or $3/2^+$.
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