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Register a new userMeasurement of the Cross Section for $e^{+}e^{-}rightarrowLambdabarLambda$ and Observation of the Decay $psi(3770)rightarrowLambdabarLambda$
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The Born cross section of the process $e^{+}e^{-}rightarrowLambdabarLambda$ 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 justification from the $psi(3770)rightarrowLambdabarLambda$ decay, which is fitted with a significance of 4.9$sigma$ with the systematic uncertainty included. The lower bound on its branching fraction is $2.4times10^{-6}$ at the 90% confidence level (C.L.), at least five times larger than expected from predictions using a simple scaling approach. This result indicates the importance of effects from vector charmonium(-like) when interpreting data in terms of {it e.g.}, electromagnetic structure observables. There are no definite conclusions about the interplay with other vector charmonium(-like), and we set 90% C.L.upper limits for the products of the electronic widths and the branching fractions.
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We report new measurements of the cross sections for the production of D Dbar final states at the psi(3770) resonance. Our data sample consists of an integrated luminosity of 2.93/fb of e+e- annihilation data produced by the BEPCII collider and colle
cted and analyzed with the BESIII detector. We exclusively reconstruct three D0 and six D+ hadronic decay modes and use the ratio of the yield of fully reconstructed D Dbar events (double tags) to the yield of all reconstructed D or Dbar mesons (single tags) to determine the number of D0 D0bar and D+D- events, benefiting from the cancellation of many systematic uncertainties. Combining these yields with an independent determination of the integrated luminosity of the data sample, we find the cross sections to be sigma(e+e- --> D0 D0bar)=(3.615 +- 0.010 +- 0.038) nb and sigma(e+e- --> D+D-)=(2.830 +- 0.011 +- 0.026) nb, where the uncertainties are statistical and systematic, respectively.
Using a total of 11.0 fb$^{-1}$ of $e^{+}e^{-}$ collision data with center-of-mass energies between 4.009 GeV and 4.6 GeV and collected with the BESIII detector at BEPCII, we measure fifteen exclusive cross sections and effective form factors for the process $e^{+}e^{-}rightarrowXi^{-}barXi^{+}$ by means of a single baryon-tag method. After performing a fit to the dressed cross section of $e^{+}e^{-}rightarrowXi^{-}barXi^{+}$, no significant $psi(4230)$ or $psi(4260)$ resonance is observed in the $Xi^{-}barXi^{+}$ final states, and upper limits at the 90% confidence level on $Gamma_{ee}mathcal{B}$ for the processes $psi(4230)$/$psi(4260)rightarrowXi^{-}barXi^{+}$ are determined. In addition, an excited $Xi$ baryon at 1820 MeV/$c^{2}$ is observed with a statistical significance of 6.2 $sim$ 6.5$sigma$ by including the systematic uncertainty, and the mass and width are measured to be $M = (1825.5 pm 4.7 pm 4.7)$~MeV/$c^{2}$ and $Gamma = (17.0 pm 15.0 pm 7.9)$~MeV, which confirms the existence of the $J^{P}=frac{3}{2}^{-}$ state $Xi(1820)$.
Using 281 /pb of e^+ e^- collisions recorded at the psi(3770) resonance with the CLEO-c detector at CESR, we determine absolute hadronic branching fractions of charged and neutral D mesons using a double tag technique. Among measurements for three D^0 and six D^+ modes, we obtain reference branching fractions B(D^0 --> K^-pi^+) = (3.891 +- 0.035 +- 0.059 +- 0.035)% and B(D^+ --> K^-pi^+pi^+) = (9.14 +- 0.10 +- 0.16 +- 0.07)%, where the first uncertainty is statistical, the second is all systematic errors other than final state radiation (FSR), and the third is the systematic uncertainty due to FSR. We include FSR in these branching fractions by allowing for additional unobserved photons in the final state. Using an independent determination of the integrated luminosity, we also extract the cross sections sigma(e+e- --> D^0 D^0-bar) = (3.66+- 0.03 +- 0.06) nb and sigma(e+e- --> D^+ D^-) = (2.91+- 0.03 +- 0.05) nb at a center of mass energy, E_cm = 3774 +- 1 MeV.
Using data samples collected with the BESIII detector operating at the BEPCII collider at center-of-mass energies from 3.810 to 4.600 GeV, we perform a study of $e^{+}e^{-} to eta J/psi$ and $pi^0 J/psi$. Statistically significant signals of $e^{+}e^{-} to eta J/psi$ are observed at $sqrt{s}$ = 4.190, 4.210, 4.220, 4.230, 4.245, 4.260, 4.360 and 4.420 GeV, while no signals of $e^{+}e^{-} to pi^{0} J/psi$ are observed. The measured energy-dependent Born cross section for $e^{+}e^{-} to eta J/psi$ shows an enhancement around 4.2~GeV. The measurement is compatible with an earlier measurement by Belle, but with a significantly improved precision.
The cross section of the process $e^+e^- rightarrow etaJ/psi$ is measured at center-of-mass energies from $sqrt{s} =$ 4.178 to 4.600 GeV using data samples corresponding to a total integrated luminosity of 11 fb$^{-1}$ collected with the BESIII detector operating at the BEPCII storage ring. The dependence of the cross section on $sqrt{s}$ shows an enhancement around $4.2$ GeV. While the shape of the cross section cannot be fully explained with a single $psi(4160)$ or $psi(4260)$ state, a coherent sum of the two states does provide a reasonable description of the data.
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