https://doi.org/10.1140/epjc/s10052-021-09416-x
Regular Article - Theoretical Physics
The 
pentaquark from a combined effective field theory and phenomenological perspective
1
School of Physics, Beihang University, 100191, Beijing, China
2
Centre d’Études Nucléaires, CNRS/IN2P3, Université de Bordeaux, 33175, Gradignan, France
3
International Research Center for Nuclei and Particles in the Cosmos and Beijing Key Laboratory of Advanced Nuclear Materials and Physics, Beihang University, 100191, Beijing, China
Received:
16
March
2021
Accepted:
5
July
2021
Published online:
29
July
2021
The observation of the by the LHCb collaboration adds a new member to the set of known hidden-charm pentaquarks, which includes the 
, 
and 
. The is expected to have the light-quark content of a 
baryon (
, 
), but its spin is unknown. Its closeness to the 
threshold – 
in the isospin-symmetric limit – suggests the molecular hypothesis as a plausible explanation for the . While in the absence of coupled-channel dynamics heavy-quark spin symmetry predicts the two spin-states of the to be degenerate, power counting arguments indicate that the coupling with the nearby 
and 
channels might be a leading order effect. This generates a hyperfine splitting in which the 
pentaquark will be lighter than the 
configuration, which we estimate to be of the order of 
. We also point out an accidental symmetry between the and 
potentials. Finally, we argue that the spectroscopy and the 
decays of the might suggest a marginal preference for 
over 
.
© The Author(s) 2021
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