Pentaquark Search and Other Multiquark Candidates at BES

TL;DR

This paper reports on searches for pentaquark states and other multiquark candidates in J/psi and psi(2S) decays, setting upper limits on pentaquark signals and observing various mass spectrum enhancements.

Contribution

It provides the first search results for the pentaquark candidate Theta(1540) in these decay channels and reports new observations of mass spectrum enhancements near certain thresholds.

Findings

No evidence for Theta(1540) pentaquark was observed.

A narrow enhancement near 2m_p in p p̄ invariant mass spectrum.

Enhancements near m_p + M_Λ and m_K + m_Λ thresholds were observed.

Abstract

Results are presented on $\psi(2S)$ and $J/\psi$ hadronic decays to $K^0_SpK^-\bar n$ and $K^0_S\bar p K^+n$ final states from data samples of 14 million $\psi(2S)$ and 58 million $J/\psi$ events accumulated at the BES II detector. No $\Theta(1540)$ signal, the pentaquark candidate, is observed, and the upper limits are set. We also present a narrow enhancement near $2m_p$ in the invariant mass spectrum of $p \bar{p}$ pairs from $J/\psi \to \gamma p \bar{p}$ decays, an enhancement near the $m_p + M_{\Lambda}$ mass threshold and an enhancement near the $m_K + m_{\Lambda}$ mass threshold from $J/\psi \to p K^- \bar{\Lambda} + c.c.$ decays, based on 58 million $J/\psi$ events.