Studying triangle singularity through spin observables

In this work, we study the spin density matrix element rho(00) of the phi in the decay J/psi -> eta pi phi In previous studies, a band around 1.4 GeV on the pi(0)phi distribution in Dalitz plot was reported by the BESIII Collaboration. This structure may be caused by the production of a resonance or the triangle singularity mechanism. We find that the predictions of the spin density matrix elements of the final phi based on these mechanisms show distinct features. Thus the measurement of the spin density matrix elements of the phi in this reaction may offer an alternative way to study the triangle singularity and to clarify the reaction mechanisms, i.e., resonance production or kinematic effects. This work also shows the potential of spin observables in studying kinematic singularities.

Automated summary

In this work, the spin density matrix element rho(00) of phi in the decay J/psi -> eta pi phi is studied. The measurement of this spin density matrix element offers an alternative way to study triangle singularity and clarify reaction mechanisms. This work also demonstrates the potential of using spin observables to study kinematic singularities.