Measurements of $\psi(3686) \to K^{-} \Lambda \bar{\Xi}^{+} +c.c.$ and $\psi(3686) \to \gamma K^{-} \Lambda \bar{\Xi}^{+} +c.c$

TL;DR

This paper reports the first measurements of specific decay processes of the $\psi(3686)$ particle, including the observation of hyperons $\Xi(1690)^-$ and $\Xi(1820)^-$, using a large data sample from the BESIII detector.

Contribution

First measurement of branching fractions and hyperon states in $\psi(3686)$ decays involving $K^-\Lambdaar{\Xi}^+$ final states.

Findings

Observation of $\Xi(1690)^-$ and $\Xi(1820)^-$ hyperons with significances of 4.9σ and 6.2σ.

First measurement of branching fractions for $\psi(3686)$ decays to these hyperon states.

Identification of new decay channels involving $\chi_{cJ}$ states.

Abstract

Using a sample of $1.06\times10^8\ \psip$ events produced in $e^+e^-$ collisions at $\sqrt{s}$ = 3.686 GeV and collected with the BESIII detector at the BEPCII collider, we present studies of the decays $\klx+c.c.$ and $\gklx+c.c.$. We observe two hyperons, $\Xi(1690)^-$ and $\Xi(1820)^-$, in the $K^-\Lambda$ invariant mass distribution in the decay $\klx+c.c.$ with significances of $4.9 \sigma$ and $6.2 \sigma$, respectively. The branching fractions of $\klx+c.c.$, $\ksx+c.c.$, $\psip\to\gamma \chi_{cJ}\to \gamma K^- \Lambda \bar{\Xi}^+ +c.c.$ $(J=0,\ 1,\ 2)$, and $\psip\to \Xi(1690/1820)^{-} \bar{\Xi}^++c.c$ with subsequent decay $\Xi(1690/1820)^-\to K^-\Lambda$ are measured for the first time.