Evidence for the Cusp Effect in ${\eta }^{\prime }$ Decays into $\eta {\pi }^0{\pi }^0$

Abstract

Using a sample of $4.3\times 10^5$ ${\eta }^{\prime }\to \eta {\pi }^0{\pi }^0$ events selected from the ten billion $J/\psi$ event dataset collected with the BESIII detector, we study the decay ${\eta }^{\prime }\to \eta {\pi }^0{\pi }^0$ within the framework of nonrelativistic effective field theory. Evidence for a structure at ${\pi }^{+}{\pi }^{-}$ mass threshold is observed in the invariant mass spectrum of ${\pi }^0{\pi }^0$ with a statistical significance of around $3.5\sigma$, which is consistent with the cusp effect as predicted by the nonrelativistic effective field theory. After introducing the amplitude for describing the cusp effect, the $\pi \pi$ scattering length combination $a_0-a_2$ is determined to be $0.226\pm 0.060_{\mathrm{stat}}\pm 0.013_{\mathrm{syst}}$, which is in good agreement with theoretical calculation of $0.2644\pm 0.0051$.

References in corpus (10)

• Cusps in K --> 3 pi decays
• Number of $J/\psi$ events at BESIII
• Radiative corrections in K --> 3 pi decays
• Cusps in K_L --> 3 pi decays
• Determination of the Dalitz plot parameter alpha for the decay eta->3pi^0 with the Crystal Ball at MAMI-B
• The cusp effect in eta' --> eta pi pi decays
• K -> 3 pi Final State Interactions at NLO in CHPT and Cabibbo's Proposal to Measure a_0-a_2
• What can we learn about light-meson interactions at electron-positron colliders?
• Detailed Study of the KL -> 3pi0 Dalitz Plot
• Measurement of the matrix elements for the decays ${\eta }^{\prime }\to \eta {\pi }^{+}{\pi }^{-}$ and ${\eta }^{\prime }\to \eta {\pi }^0{\pi }^0$

Cited by in corpus (2)

• Precision measurement of the matrix elements for $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ and $\eta \to {\pi }^0{\pi }^0{\pi }^0$ decays
• Novel method for determining the light quark mass ratio using ${\eta }^{\prime }\to \eta \pi \pi$ decays