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Title: Spin and parity of the Pc(4440) and Pc(4457) pentaquarks
Plain: 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: $\mathrm{Pc}(4440)+$ 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.
Settled by: 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.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: open
Status note: No spin-parity determination of either state had been published, to our knowledge, as of mid-2026.
Posed since: 2019