Measurement of the spin of the Ξ(1530) resonance

The properties of the Ξ(1530) resonance are investigated in the Λc+→Ξ-π+K+ decay process. The data sample was collected with the BABAR detector at the SLAC PEP-II asymmetric-energy e+e- collider operating at center-of-mass energies 10.58 and 10.54 GeV. The corresponding integrated luminosity is approximately 230  fb-1. The spin of the Ξ(1530) is established to be 3/2. The existence of an S-wave amplitude in the Ξ-π+ system is inferred, and its interference with the Ξ(1530)0 amplitude provides the first clear demonstration of the Breit-Wigner phase motion expected for the Ξ(1530). The P1(cos⁡θΞ-) Legendre polynomial moment indicates the presence of a significant S-wave amplitude for Ξ-π+ mass values above 1.6  GeV/c2, and a dip in the mass distribution at approximately 1.7  GeV/c2 is interpreted as due to the coherent addition of a Ξ(1690)0 contribution to this amplitude. This would imply JP=1/2- for the Ξ(1690). Attempts at fitting the Ξ(1530)0 line shape yield unsatisfactory results, and this failure is attributed to interference effects associated with the amplitudes describing the K+π+ and/or Ξ-K+ systems.