Abstract
The process $e^+ e^- \to \phi \Lambda \bar{\Lambda}$ is studied using data samples collected with the BESIII detector at the BEPCII collider at center-of-mass energies $\sqrt{s}$ ranging from $3.51$ to $4.60~{\rm GeV}$ . An intermediate resonance structure is observed near the threshold of $\Lambda \bar{\Lambda}$. It has a mass of $(2262 \pm 4 \pm 28)~{\rm{MeV}}/c^{2}$ and a width of $(72 \pm 5 \pm 43)~\rm{MeV}$, where the quoted uncertainties are statistical and systematic, respectively. The $J^{PC}$ quantum numbers of $0^{-+}$ and $0^{++}$ are rejected, while other $J^{PC}$ hypotheses are possible, according to the helicity angle study. The energy-dependent cross section of the $e^+ e^- \to \phi \Lambda \bar{\Lambda}$ process is measured for the first time in this energy region, and contributions from excited $\psi$ states and vector charmonium-like $Y$-states are investigated.
Highlights
In this 21st century, a number of exotic states were discovered [1] in final states with a quarkonium and one or two light hadrons, or with heavy-flavor mesons
The rising rate of the reversed exponential function is measured as 33 Æ 11 Æ 6 MeV=c2
In 2017, a dedicated analysis performed by the BESIII experiment revealed that the so-called Yð4260Þ state is not one Breit-Wigner (BW) resonance and can be a combination of two states [7]
Summary
In this 21st century, a number of exotic states were discovered [1] in final states with a quarkonium and one or two light hadrons, or with heavy-flavor mesons Among these states, there are vector states with JPC 1⁄4 1−− which are usually called Y states, such as the Yð4260Þ [2], Yð4360Þ [3,4], and Yð4660Þ [3]. If the ccquarks in Yð4260Þ annihilate while the sspair survives in the final state, we expect Yð4260Þ decays into strange mesons or baryons, such as φΛΛ Such a signal will manifest itself as a line shape distortion due to the interference between the amplitudes of the Yð4260Þ decay and the eþe− → φΛΛcontinuum production. The vector charmonium/charmoniumlike states are studied based on the energy-dependent cross sections, and an intermediate state in the ΛΛsystem is investigated to extract information on light mesons
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