Measurement of the Energy-Dependent Electromagnetic Form Factors of a Charmed Baryon

Abstract

We study the process $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$ at twelve center-of-mass energies from $4.6119$ to $4.9509\mathrm{GeV}$ using data samples collected by the BESIII detector at the BEPCII collider. The Born cross sections and effective form factors ($|G_{\mathrm{eff}}|$) are determined with unprecedented precision after combining the single and double-tag methods based on the decay process ${\Lambda }_c^{+}\to p{K}^{-}{\pi }^{+}$. Flat cross sections around $4.63\mathrm{GeV}$ are obtained and no indication of the resonant structure $Y(4630)$, as reported by Belle, is found. In addition, no oscillatory behavior is discerned in the $|G_{\mathrm{eff}}|$ energy-dependence of ${\Lambda }_c^{+}$, in contrast to what is seen for the proton and neutron cases. Analyzing the cross section together with the polar-angle distribution of the ${\Lambda }_c^{+}$ baryon at each energy point, the moduli of electric and magnetic form factors ($|G_E|$ and $|G_M|$) are extracted and separated. For the first time, the energy-dependence of the form factor ratio $|G_E/G_M|$ is observed, which can be well described by an oscillatory function.

10 pages, 3 figures

References in corpus (22)

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• New Features in the Electromagnetic Structure of the Neutron
• Measurement of the proton form factor by studying $e^{+}{e}^{-}\to p\bar{p}$
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• Measurement of proton electromagnetic form factors in the time-like region using initial state radiation at BESIII
• Dispersion-theoretical analysis of the electromagnetic form factors of the nucleon: Past, present and future
• On the strong energy dependence of the e^+e^- to ppbar amplitude near threshold
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• Are the $Y$ states around 4.6 GeV from $e^{+}{e}^{-}$ annihilation higher charmonia?
• Measurement of the cross section for $e^{+}{e}^{-}\to \Lambda \bar{\Lambda }$ and evidence of the decay $\psi (3770)\to \Lambda \bar{\Lambda }$
• New fit of time-like proton electromagnetic form factors from $e^{+}{e}^{-}$ colliders
• Re-examining the $X(4630)$ resonance in the reaction $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$
• Probing the internal structure of baryons
• Measurement of $\Lambda$ baryon polarization in $e^{+}{e}^{-}\to \Lambda \bar{\Lambda }$ at $\sqrt{s}=3.773$ GeV
• Timelike nucleon electromagnetic form factors: All about interference of isospin amplitudes
• Final-state interaction in the process $e^{+}{e}^{-}\to {\Lambda }_c{\bar{\Lambda }}_c$
• The electromagnetic form factors of ${\Lambda }_c$ hyperon in the vector meson dominance model
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• Global coupled-channel analysis of $e^{+}{e}^{-}\to c\bar{c}$ processes in $\sqrt{s}=3.75-4.7$ GeV
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• $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$ cross sections and the ${\Lambda }_c^{+}$ electromagnetic form factors within the extended vector meson dominance model
• Production of $D^{(\ast )}{\bar{D}}^{(\ast )}$ near the thresholds in $e^{+}{e}^{-}$ annihilation
• First observation of ${\Lambda }_c^{+}\to \Lambda K^{+}{\pi }^0$ and evidence of ${\Lambda }_c^{+}\to \Lambda K^{+}{\pi }^{+}{\pi }^{-}$
• The electromagnetic form factors and spin polarization of ${\Lambda }_c^{+}$ in the process $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\bar{\Lambda }}_c^{-}$
• Measurement of the branching fractions of the decays ${\Lambda }_c^{+}\to \Lambda K_S^0{K}^{+}$, ${\Lambda }_c^{+}\to \Lambda K_S^0{\pi }^{+}$ and ${\Lambda }_c^{+}\to \Lambda K^{\ast +}$
• Measurements of Born Cross Sections for $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\bar{\Lambda }}_c(2595{)}^{-}+c.c.$ and $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\bar{\Lambda }}_c(2625{)}^{-}+c.c.$ at $\sqrt{s}=$4918.0 and 4950.9 MeV
• Measurement of Born cross section of $e^{+}{e}^{-}\to {\Sigma }^0{\bar{\Sigma }}^0$ at $\sqrt{s}=3.50-4.95$ GeV
• First observation of the decay ${\Lambda }_c^{+}\to n{K}_S^0{\pi }^{+}{\pi }^0$
• Search for $e^{+}{e}^{-}\to \varphi {\chi }_{c0}$ and $\varphi {\eta }_{c2}(1D)$ at center-of-mass energies from 4.47 to 4.95 GeV
• Search for the Cabibbo-suppressed decays ${\Lambda }_c^{+}\to {\Sigma }^0{K}^{+}{\pi }^0$ and ${\Lambda }_c^{+}\to {\Sigma }^0{K}^{+}{\pi }^{+}{\pi }^{-}$
• Puzzles in charmed baryon semileptonic decays with $SU(3{)}_F$ flavor symmetry and lattice inputs