Measurement of the cross section for $e^{+}{e}^{-}\to \Lambda \bar{\Lambda }$ and evidence of the decay $\psi (3770)\to \Lambda \bar{\Lambda }$

Abstract

The Born cross section of the process $e^{+}{e}^{-}\to \Lambda \bar{\Lambda }$ is measured at 33 center-of-mass energies between 3.51 and 4.60 GeV using data corresponding to the total integrated luminosity of 20.0 fb${}^{-1}$ collected with the BESIII detector at the BEPCII collider. Describing the energy dependence of the cross section requires a contribution from the $\psi (3770)\to \Lambda \bar{\Lambda }$ decay, which is fitted with a significance of 4.6-4.9$\sigma$ including the systematic uncertainty. The lower bound on its branching fraction is $2.4\times 10^{-6}$ at the 90% confidence level (C.L.), at least an order of magnitude larger than expected from predictions using a scaling based on observed electronic widths. This result indicates the importance of effects from vector charmonium(-like) states when interpreting data in terms of e.g., electromagnetic structure observables. The data do not allow for definite conclusions on the interplay with other vector charmonium(-like) states, and we set 90% C.L.upper limits for the products of their electronic widths and the branching fractions.

arXiv comment8 pages, 4 Figures, 1 Supplemental Material with 2 pages, consistent with paper published in Phys. Rev. D 104, L091104 (2021)

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• Timelike nucleon electromagnetic form factors: All about interference of isospin amplitudes
• First simultaneous measurement of ${\Xi }^0$ and ${\bar{\Xi }}^0$ asymmetry parameters in $\psi (3686)$ decay
• Precise Measurement of Born Cross Sections for $e^{+}{e}^{-}\to D\bar{D}$ at $\sqrt{s}=3.80-4.95$ GeV
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• Electromagnetic form factors of neutron and neutral stange hyperons in the oscillating view of point
• Production and decay of polarized hyperon-antihyperon pairs
• Measurement of the cross section of $e^{+}{e}^{-}\to {\Xi }^{-}{\bar{\Xi }}^{+}$ at center-of-mass energies between 3.510 and 4.843 GeV
• Impact of the interference between the resonance and continuum amplitudes on vector quarkonia decay branching fraction measurements
• Compared analysis of time-like hyperon form factors
• Measurement of $e^{+}{e}^{-}\to \Lambda \bar{\Lambda }\eta$ from 3.5106 to 4.6988 GeV and study of $\Lambda \bar{\Lambda }$ mass threshold enhancement
• The cross section of the process $e^{+}{e}^{-}\to \Lambda \bar{\Lambda }$ in the vicinity of charmonium $\psi (3770)$ including three-gluon and $D$-meson loop contributions
• The electromagnetic form factors and spin polarization of ${\Lambda }_c^{+}$ in the process $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$
• Measurement of Born cross section of $e^{+}{e}^{-}\to {\Sigma }^0{\bar{\Sigma }}^0$ at $\sqrt{s}=3.50-4.95$ GeV
• Unraveling the structure of $\Lambda$ hyperons with polarized $\Lambda \bar{\Lambda }$ pairs
• Observation of Transverse Polarization and Determination of Psionic Form Factors of the $\Lambda$ Hyperon at $\sqrt{s}=3.773$ GeV
• Dissociation cross sections of $\psi (3770)$, $\psi (4040)$, $\psi (4160)$, and $\psi (4415)$ mesons with nucleons
• Baryon Form Factors
• Time-like electromagnetic form factors of $\Lambda ,\Sigma$ and ${\Xi }^{+}$ in a light-front quark model