Pole determination of PψSΛ (4338) and possible PψSΛ (4255) in B- → J/ψΛ(p)over-bar

The first hidden-charm pentaquark candidate with strangeness, P psi(Lambda)(s)(4338), was recently discovered in B- -> J/psi Lambda(p) over bar by the LHCb Collaboration. P psi(Lambda)(s)(4338) shows up as a bump at the Xi(c)(D) over bar threshold in the J/psi Lambda invariant mass (M-J/psi Lambda) distribution. The MJ(/psi Lambda) distribution also shows a large fluctuation at the Lambda(c)(D) over bar (s) threshold, hinting the existence of a possible P psi(Lambda)(s)(4255). In this work, we determine the P psi(Lambda)(s) (4338) and P psi(Lambda)(s)(4255) pole positions for the first time. For this purpose, we fit a B- -> J/psi Lambda(p) over bar model to the M-J/psi Lambda, MJ(/psi(p) over bar), and M Lambda((p) over bar) and cos theta(K*) distributions from the LHCb simultaneously; chi(2)/ndf similar to 1.21. Then we extract P-psi s(Lambda) poles from a unitary Xi(c)(D) over bar-Lambda(c)(D) over bar (s) coupled-channel scattering amplitude built in the model. In our default fit, the P psi(s)Lambda (4338) pole is found at (4338.2 +/- 1.4)-(1.9 +/- 0.5)(i) MeV while the P psi(Lambda)(s)(4255) pole at 4254.7 +/- 0.4 MeV. The P psi(Lambda)(s) (4338) and P psi(Lambda)(s)(4255) are mostly Xi(c)(D) over bar bound and Lambda(c)(D) over bar (s) virtual states, respectively. Through our analysis, the data disfavors a hypothesis of P psi(Lambda)(s)(4338) as merely a kinematical effect. This pole determination, which is important in its own right, sets a primary basis to study the nature of the P psi(Lambda)(s) states.

Automated summary

In the B- -> J/psi Lambda(p) over bar experiment, the first hidden-charm pentaquark candidate with strangeness, P psi(Lambda)(s)(4338), was discovered. By fitting the experimental data, the pole positions of P psi(Lambda)(s)(4338) and P psi(Lambda)(s)(4255) were determined for the first time. The analysis ruled out the hypothesis that P psi(Lambda)(s)(4338) is solely a kinematical effect.