First Determination of the Spin-Parity of (Formula presented) Baryons

The (Formula presented) decay chains are observed, and the spin-parity of (Formula presented) baryons is determined for the first time. The measurement is performed using proton-proton collision data at a center-of-mass energy of (Formula presented), corresponding to an integrated luminosity of (Formula presented), recorded by the LHCb experiment between 2016 and 2018. The spin-parity of the (Formula presented) baryons is determined to be (Formula presented) with a significance of more than (Formula presented) ((Formula presented)) compared to all other tested hypotheses. The up-down asymmetries of the (Formula presented) transitions are measured to be (Formula presented) ((Formula presented)), consistent with maximal parity violation, where the first uncertainty is statistical and the second is systematic. These results support the hypothesis that the (Formula presented) baryons correspond to the first (Formula presented)-wave (Formula presented)-mode excitation of the (Formula presented) flavor triplet.