The pi-pi mass spectrum in Y(4260) -> pi-pi-J/psi

TL;DR

This paper investigates different models to fit the pi-pi mass spectrum in Y(4260) decays, finding that some models require arbitrary interference terms or propose new intermediate states, with data analysis limitations noted.

Contribution

It introduces alternative fitting approaches for the pi-pi spectrum in Y(4260) decays, including a new decay sequence hypothesis involving a hypothetical state H.

Findings

Data cannot be fitted by elastic pi-pi S-wave intensity alone.

Adding a destructive interference with the sigma pole improves the fit.

A decay sequence involving a new state H provides a better fit.

Abstract

Three ways of fitting the pi-pi mass spectrum in Y(4260) decays are studied. Data presented recently by Belle cannot be fitted by the pi-pi S-wave intensity for elastic scattering. They can be fitted by adding a rather arbitrary destructive interference with the sigma pole term. A better fit may be obtained with the decay sequence Y -> pi-H, H -> pi-J/psi, where H is a JPC=1-- c-cbar-q-qbar state peaking at 4.0 GeV with a width ~280 MeV. A third possibility, involving a triangle diagram due to Y(4260)-> DD_1(2420), D_1->D*(2007)-pi, DD*->pi-J/psi fails to fit the data. The first and second possibilities could be resolved by analysis of the Y(4260) Dalitz plot and pi-J/psi mass projection, not presently publicly available.