Measurement of the Spin of the Xi(1530) Resonance

TL;DR

This study measures the spin of the Xi(1530) resonance, confirms it to be 3/2, and explores interference effects revealing insights into its decay dynamics and related resonances.

Contribution

It provides the first clear demonstration of the Breit-Wigner phase motion for Xi(1530) and investigates S-wave contributions and interference effects in its decay.

Findings

Confirmed Xi(1530) spin as 3/2

Identified S-wave amplitude in Xi- pi+ system

Observed interference effects affecting lineshape fits

Abstract

The properties of the Xi(1530) resonance are investigated in the Lambdac+ --> Xi- pi+ 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 inverse fb. The spin of the Xi(1530) is established to be 3/2. The existence of an S-wave amplitude in the Xi- pi+ system is inferred, and its interference with the Xi(1530)0 amplitude provides the first clear demonstration of the Breit-Wigner phase motion expected for the Xi(1530). The P_1(cos[theta(Xi-)]) Legendre polynomial moment indicates the presence of a significant S-wave amplitude for Xi- pi+ mass values above 1.6 GeV/c^2, and a dip in the mass distribution at approximately 1.7 GeV/c^2 is interpreted as due to coherent addition of a Xi(1690)0 contribution to this amplitude. This would imply J^P=1/2^- for the Xi(1690). Attempts at fitting the Xi(1530)0 lineshape yield unsatisfactory results, and this failure is attributed to interference effects associated with the amplitudes describing the K+ pi+ and/or Xi- K+ systems.