Spin and parity of the Pc(4440) and Pc(4457) pentaquarks
In plain words
LHCb found in 2019 that one pentaquark signal is two close peaks, at 4440 and 4457 MeV, both just below the energy of a charmed baryon plus a charmed meson. Molecular models predict spins $1/2$ and $3/2$ for this pair while compact models give other patterns, so measuring the spins tests the pictures.
Precise statement
$\mathrm{Pc}(4440)+$ and $\mathrm{Pc}(4457)+$ appear in $J/\psi\,p$ from $\Lambda_{b} \to J/\psi\,p\,K-$ (LHCb, PRL 122, 222001, 2019), about 20 and 3 MeV below the Sigma_c+ anti-D*0 threshold. Determine $J^{P}$ of each from a full amplitude analysis. Answer: $J^{P}$ values; the Sigma_c anti-D* molecular picture predicts $1/2-$ and $3/2-$, with the ordering set by short-range contact terms.
What would settle it
A full amplitude analysis of $\Lambda_b \to \mathrm{J}/\psi\, \mathrm{p}\, \mathrm{K}-$ with LHCb Run 3 statistics, cross-checked in a second production channel.
Status in the literature
Unverified note
No spin-parity determination of either state had been published, to our knowledge, as of mid-2026.