First determination of the spin-parity of ${\Xi}_{c}(3055)^{+,0}$ baryons

TL;DR

This paper reports the first measurement of the spin-parity of ${ m ext{ extXi}_c}(3055)$ baryons, confirming they are $3/2^+$ states, using decay data from proton-proton collisions at 13 TeV recorded by LHCb.

Contribution

The study provides the first determination of the spin-parity of ${ m ext{ extXi}_c}(3055)$ baryons, identifying them as $3/2^+$ states and supporting their interpretation as D-wave $ ext{ extLambda}$-mode excitations.

Findings

${ m extXi}_c(3055)$ baryons have spin-parity $3/2^+$ with >6.5$\sigma$ significance.

Measured up-down asymmetries indicate maximal parity violation.

Results support the D-wave $ ext{ extLambda}$-mode excitation hypothesis.

Abstract

The ${{\Xi}_{b}^{0(-)}\to{\Xi}_{c}(3055)^{+(0)}(\to D^{+(0)}{\Lambda}){\pi}^{-}}$ decay chains are observed, and the spin-parity of ${\Xi}_{c}(3055)^{+(0)}$ baryons is determined for the first time. The measurement is performed using proton-proton collision data at a center-of-mass energy of $\sqrt{s}=13\,\text{TeV}$, corresponding to an integrated luminosity of $5.4\,\text{fb}^{-1}$, recorded by the~$\text{LHCb}$ experiment between 2016 and 2018. The spin-parity of the ${\Xi}_{c}(3055)^{+(0)}$ baryons is determined to be $3/2^{+}$ with a significance of more than $6.5\sigma$ ($3.5\sigma$) compared to all other tested hypotheses. The up-down asymmetries of the ${{\Xi}_{b}^{0(-)}\to{\Xi}_{c}(3055)^{+(0)}{\pi}^{-}}$ transitions are measured to be $-0.92\pm0.10\pm0.05$ ($-0.92\pm0.16\pm0.22$), consistent with maximal parity violation, where the first uncertainty is statistical and the second is systematic. These results support the hypothesis that the ${\Xi}_{c}(3055)^{+(0)}$ baryons correspond to the first $D$-wave $\lambda$-mode excitation of the ${\Xi}_{c}$ flavor triplet.