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Register a new userPrecision measurement of the $e^{+}e^{-}~rightarrow~Lambda_{c}^{+} bar{Lambda}_{c}^{-}$ cross section near threshold
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The Born cross section of the $e^{+}e^{-}~rightarrow~Lambda_{c}^{+} bar{Lambda}_{c}^{-}$ process is measured with unprecedented precision using data collected with the BESIII detector at $sqrt{s}=4574.5$, $45580.0$, $4590.0$ and $4599.5$ $mathrm{MeV}$. The non-zero cross section near the $Lambda_{c}^{+} bar{Lambda}_{c}^{-}$ production threshold is discerned. At center-of-mass energies $sqrt{s}=4574.5$ and $4599.5 $ $mathrm{MeV}$, the higher statistics data enable us to measure the $Lambda_{c}$ polar angle distributions. From these, the ratio between the $Lambda_{c}$ electric and magnetic form factors ($|G_{E}/G_{M}|$) is measured for the first time. They are found to be $1.14pm0.14pm0.07$ and $1.23pm0.05pm0.03$ respectively, where the first uncertainties are statistical and the second are systematic.
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Using $e^+e^-$ collision data at ten center-of-mass energies between 2.644 and 3.080 GeV collected with the BESIII detector at BEPCII and corresponding to an integrated luminosity of about 500 pb$^{-1}$, we measure the cross sections and effective form factors for the process $e^{+}e^{-}rightarrowXi^{0}bar{Xi}^{0}$ utilizing a single-tag method. A fit to the cross section of $e^{+}e^{-}rightarrowXi^{0}bar{Xi}^{0}$ with a pQCD-driven power function is performed, from which no significant resonance or threshold enhancement is observed. In addition, the ratio of cross sections for the processes $e^{+}e^{-}rightarrowXi^{-}bar{Xi}^{+}$ and $Xi^{0}bar{Xi}^{0}$ is calculated using recent BESIII measurement and is found to be compatible with expectation from isospin symmetry.
The Born cross-sections and effective form factors for process $e^+e^-toXi^-bar{Xi}^+$ are measured at eight center-of-mass energies between 2.644 and 3.080 GeV, using a total integrated luminosity of 363.9 pb$^{-1}$ $e^+e^-$ collision data collected with the BESIII detector at BEPCII. After performing a fit to the Born cross-section of $e^+e^-toXi^-bar{Xi}^+$, no significant threshold effect is observed.
The process $e^{+}e^{-}rightarrowLambdabar{Lambda}$ is studied using data samples at $sqrt{s}=2.2324$, 2.400, 2.800 and 3.080 GeV collected with the BESIII detector operating at the BEPCII collider. The Born cross section is measured at $sqrt{s}$=2.2324 GeV, which is 1.0 MeV above the $Lambdabar{Lambda}$ mass threshold, to be $305pm45^{+66}_{-36}$ pb, where the first uncertainty is statistical and the second systematic. The substantial cross section near threshold is significantly larger than that expected from theory, which predicts the cross section to vanish at threshold. The Born cross sections at $sqrt{s}$=2.400, 2.800 and 3.080 GeV are measured and found to be consistent with previous experimental results, but with improved precision. Finally, the corresponding effective electromagnetic form factors of $Lambda$ are deduced.
We report the first observation of the $Xi_{c}(2930)^0$ charmed-strange baryon with a significance greater than 5$sigma$. The $Xi_{c}(2930)^0$ is found in its decay to $K^- Lambda_{c}^+$ in $B^{-} to K^{-} Lambda_{c}^{+} bar{Lambda}_{c}^{-}$ decays. The measured mass and width are $[2928.9 pm 3.0(rm stat.)^{+0.9}_{-12.0}(rm syst.)]$ MeV/$c^{2}$ and $[19.5 pm 8.4(rm stat.) ^{+5.9}_{-7.9}(rm syst.)]$ MeV, respectively, and the product branching fraction is ${cal B}(B^{-} to Xi_{c}(2930)^0 bar{Lambda}_{c}^{-}) {cal B}(Xi_{c}(2930)^0 to K^- Lambda_{c}^{+})=[1.73 pm 0.45(rm stat.) pm 0.21(rm syst.)]times 10^{-4}$. We also measure ${cal B}(B^{-} to K^{-} Lambda_{c}^{+} bar{Lambda}_{c}^{-}) = [4.80 pm 0.43(rm stat.) pm 0.60(rm syst.)] times 10^{-4}$ with improved precision, and search for the charmonium-like state $Y(4660)$ and its spin partner, $Y_{eta}$, in the $Lambda_{c}^{+}bar{Lambda}_{c}^{-}$ invariant mass spectrum. No clear signals of the $Y(4660)$ nor its spin partner are observed and the 90% credibility level (C.L.) upper limits on their production rates are determined. These measurements are obtained from a sample of $(772pm11)times 10^{6} Bbar{B}$ pairs collected at the $Upsilon(4S)$ resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.
The ratios of the branching fractions of the decays $Lambda_{c}^{+} rightarrow p pi^{-} pi^{+}$, $Lambda_{c}^{+} rightarrow p K^{-} K^{+}$, and $Lambda_{c}^{+} rightarrow p pi^{-} K^{+}$ with respect to the Cabibbo-favoured $Lambda_{c}^{+} rightarrow p K^{-} pi^{+}$ decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb$^{-1}$: begin{align*} frac{mathcal{B}(Lambda_{c}^{+} rightarrow p pi^{-} pi^{+})}{mathcal{B}(Lambda_{c}^{+} rightarrow p K^{-} pi^{+})} & = (7.44 pm 0.08 pm 0.18),%, frac{mathcal{B}(Lambda_{c}^{+} rightarrow p K^{-} K^{+})}{mathcal{B}(Lambda_{c}^{+} rightarrow p K^{-} pi^{+})} &= (1.70 pm 0.03 pm 0.03),%, frac{mathcal{B}(Lambda_{c}^{+} rightarrow p pi^{-} K^{+})}{mathcal{B}(Lambda_{c}^{+} rightarrow p K^{-} pi^{+})} & = (0.165 pm 0.015 pm 0.005 ),%, end{align*} where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world-average value for $mathcal{B}(Lambda_{c}^{+} rightarrow p K^{-} pi^{+})$, the corresponding branching fractions are begin{align*} mathcal{B}(Lambda_{c}^{+} rightarrow p pi^{-} pi^{+}) &= (4.72 pm 0.05 pm 0.11 pm 0.25) times 10^{-3}, mathcal{B}(Lambda_{c}^{+} rightarrow p K^{-} K^{+}) &= (1.08 pm 0.02 pm 0.02 pm 0.06) times 10^{-3}, mathcal{B}(Lambda_{c}^{+} rightarrow p pi^{-} K^{+}) &= (1.04 pm 0.09 pm 0.03 pm 0.05) times 10^{-4}, end{align*} where the final uncertainty is due to $mathcal{B}(Lambda_{c}^{+} rightarrow p K^{-} pi^{+})$.
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