Detecting the pure triangle sigularity effect through the $\psi(2S) \to p \bar{p} \eta / p \bar{p} \pi^0$ process

TL;DR

This paper investigates a triangle singularity mechanism in the decay process of $ ext{psi}(2S)$ to $p ar{p} ext{eta}$ or $p ar{p} ext{pi}^0$, predicting a narrow peak in the invariant mass spectrum that can be experimentally observed.

Contribution

It provides a model-independent prediction of a narrow peak caused by triangle singularity in specific decay processes, constrained by experimental data.

Findings

A narrow peak at 1.56387 GeV in the $p ext{eta}$ invariant mass spectrum.

The peak is prominent in $p ext{eta}$ but very small in $p ext{pi}^0$ spectrum.

The effect can be observed by BESIII and STCF experiments.

Abstract

In this work, the triangle singularity mechanism is investigated in the $\psi(2S) \to p \bar{p} \eta / p \bar{p} \pi^0$ process. The triangle loop composed by $J/\psi$, $\eta$ and $p$ has a singularity in the physical kinematic range for the $\psi(2S) \to p \bar{p} \eta / p \bar{p} \pi^0$ process, and it would generate a very narrow peak in the invariant mass spectrum of $p\eta (\pi)$ around $1.56387$ GeV, which is far away from both the threshold and relative resonances. In these processes, all the involved vertices are constrained by the experimental data. Thus, we can make a precise model independent prediction here. It turns out that the peak in the $p\eta$ invariant mass spectrum is visible, while it is very small in the $p\pi^0$ invariant mass spectrum. We expect this effect shown in $p \bar{p} \eta$ final state can be observed by the Beijing Spectrometer (BESIII) and Super Tau-Charm Facility (STCF) in the future.