Study of the $J/ψ\to Λ\barΣ^0η$ reaction

TL;DR

The paper addresses the BESIII observation of an isospin-violating $J/ψ \to Λ \bar{Σ}^0 η$ decay and the prominent $ηΛ$ signal from the $Λ(1670)$ region. It adopts a chiral unitary, coupled-channel approach, treating $J/ψ$ as an $SU(3)$ singlet and deriving the initial $\bar{Σ}^0 BP$ production from dominant $\langle \bar{B} B P \rangle$ and $\langle \bar{B} P B \rangle$ structures, with the $BP$ final-state interaction generating $ηΛ$ in an $S$-wave and the $J/ψ$ polarization providing the needed $P$-wave. The analysis shows that the isospin violation is chiefly driven by $KΞ$ loops, whose charged and neutral mass differences prevent cancellation, and the $Λ(1670)$ appears as a dynamically generated state in this sector. A small incoherent contribution from $Λ(1810)(1/2^+)$ helps reproduce the high-mass tail of the spectrum, and the resulting mass distributions align well with BESIII data. Overall, the work provides a dynamical, molecular-like explanation for the observed resonance structure and isospin violation within the chiral unitary framework, highlighting the role of kaon-loop effects in hadronic decays.

Abstract

We study the isospin violating $J/ψ\to Λ\bar Σ^0 η$ reaction, recently measured by the BESIII collaboration, by looking at the dominant terms with $\bar Σ^0$ and a pair of pseudoscalar-baryon particles that form together an SU(3) singlet and can thus couple to the $J/ψ$. Next we allow these pairs to undergo final state interaction to produce the final $ηΛ$. We find that the relevant original channels are $\bar K N$ and $K Ξ$, and the non cancelation of terms involving charged and neutral particles, because of their different masses, is responsible for the reaction. With that mechanism we find a good agreement with the three experimental mass distributions.

Figures (6)

• Figure 1: Diagrams involving final state interaction of $PB$ pairs leading to the $J/\psi\to \Lambda\bar{\Sigma}^0\eta$ decay.
• Figure 2: Mechanism of $J/\psi \rightarrow \bar{\Sigma}^0 \eta \Lambda$ through $\Lambda(1810)(1/2^+)$ excitation.
• Figure 3: The three different mass distributions with $A$ or $B$ equal zero ($C=0$).
• Figure 4: results of $J/\psi\to \Lambda\bar{\Sigma}^0\eta$ decay.
• Figure 5: The differences between the charged and neutral channels for $t_i$ terms.