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Register a new userObservation of $Xi_{c}(2930)^0$ and updated measurement of $B^{-} to K^{-} Lambda_{c}^{+} bar{Lambda}_{c}^{-}$ at Belle
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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.
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We report evidence for the charged charmed-strange baryon $Xi_{c}(2930)^+$ with a signal significance of 3.9$sigma$ with systematic errors included. The charged $Xi_{c}(2930)^+$ is found in its decay to $K_{S}^{0} Lambda_{c}^+$ in the substructure of $bar{B}^{0} to K^{0}_{S} Lambda_{c}^{+} bar{Lambda}_{c}^{-}$ decays. The measured mass and width are $[2942.3 pm 4.4 (rm stat.) pm 1.5(rm syst.)]$~MeV/$c^{2}$ and $[14.8 pm 8.8(rm stat.) pm 2.5(rm syst.)]$~MeV, respectively, and the product branching fraction is $cal{B}(bar{B}^{0} to Xi_c(2930)^{+} bar{Lambda}_{c}^{-}) cal{B}(Xi_c(2930)^{+}to bar{K}^{0} Lambda_{c}^{+})=[2.37 pm 0.51 (rm stat.)pm 0.31(rm syst.)]times 10^{-4}$. We also measure $cal{B}(bar{B}^{0} to bar{K}^{0} Lambda_{c}^{+} bar{Lambda}_{c}^{-}) = [3.99 pm 0.76(rm stat.) pm 0.51(rm syst.)] times 10^{-4}$ with greater precision than previous experiments, and present the results of a 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 $Y(4660)$ or $Y_{eta}$ 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.
Using the data sample of 711 fb$^{-1}$ of $Upsilon(4S)$ on-resonance data taken by the Belle detector at the KEKB asymmetric-energy electron-positron collider, we present the first measurements of branching fractions of the decays $B^{-} to bar{Lambda}_{c}^{-} Xi_{c}^{0}$, $B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2645)^{0}$, and $B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2790)^{0} $. The signal yields for these decays are extracted from the recoil mass spectrum of the system recoiling against $bar{Lambda}_{c}^{-}$ baryons in selected $B^-$ candidates. The branching fraction of $B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2790)^{0}$ is measured to be $ (1.1 pm 0.4 pm 0.2)times 10^{-3}$, where the first uncertainty is statistical and the second systematic. The 90% credibility level upper limits on ${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}^{0})$ and ${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2645)^{0})$ are determined to be $6.5times 10^{-4}$ and $7.9times 10^{-4}$, respectively.
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.
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 $mathcal{B}(Lambda_{c}^{+} rightarrow p K^{-} pi^{+})$.
Using data samples of 89.5 and 711 fb$^{-1}$ recorded at energies of $sqrt{s}=10.52$ and $10.58$ GeV, respectively, with the Belle detector at the KEKB $e^+e^-$ collider, we report measurements of branching fractions of semileptonic decays $Xi_{c}^{0} to Xi^{-} ell^{+} u_{ell}$ ($ell=e$ or $mu$) and the $CP$-asymmetry parameter of $Xi_{c}^{0} to Xi^{-} pi^{+}$ decay. The branching fractions are measured to be ${cal B}(Xi_{c}^{0} to Xi^{-} e^{+} u_{e})=(1.31 pm 0.04 pm 0.07 pm 0.38)%$ and ${cal B}(Xi_{c}^{0} to Xi^{-} mu^{+} u_{mu})=(1.27 pm 0.06 pm 0.10 pm 0.37)%$, and the decay parameter $alpha_{Xipi}$ is measured to be $0.63 pm 0.03 pm 0.01$ with much improved precision compared to the current world average. The corresponding ratio ${cal B}(Xi_{c}^{0} to Xi^{-} e^{+} u_{e})/{cal B}(Xi_{c}^{0} to Xi^{-} mu^{+} u_{mu})$ is $1.03 pm 0.05pm 0.07$, which is consistent with the expectation of lepton flavor universality. The first measured asymmetry parameter ${cal A}_{CP} = (alpha_{Xi^{-}pi^{+}} + alpha_{bar{Xi}^{+}pi^{-}})/(alpha_{Xi^{-}pi^{+}} - alpha_{bar{Xi}^{+}pi^{-}}) = 0.024 pm 0.052 pm 0.014$ is found to be consistent with zero. The first and the second uncertainties above are statistical and systematic, respectively, while the third ones arise due to the uncertainty of the $Xi_{c}^{0} to Xi^{-} pi^+$ branching fraction.
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