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Register a new userPrecision measurement of the $Lambda_c^+$, $Xi_c^+$ and $Xi_c^0$ baryon lifetimes
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We report measurements of the lifetimes of the $Lambda_c^+$, $Xi_c^+$ and $Xi_c^0$ charm baryons using proton-proton collision data at center-of-mass energies of 7 and 8tev, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment. The charm baryons are reconstructed through the decays $Lambda_c^+to pK^-pi^+$, $Xi_c^+to pK^-pi^+$ and $Xi_c^0to pK^-K^-pi^+$, and originate from semimuonic decays of beauty baryons. The lifetimes are measured relative to that of the $D^+$ meson, and are determined to be begin{align*} tau_{Lambda_c^+} &= 203.5pm1.0pm1.3pm1.4~{rm fs}, ewline tau_{Xi_c^+} &= 456.8pm3.5pm2.9pm3.1~{rm fs}, ewline tau_{Xi_c^0} &= 154.5pm1.7pm1.6pm1.0~{rm fs}, end{align*} where the uncertainties are statistical, systematic, and due to the uncertainty in the $D^+$ lifetime. The measurements are approximately 3--4 times more precise than the current world average values. The $Lambda_c^+$ and $Xi_c^+$ lifetimes are in agreement with previous measurements; however, the $Xi_c^0$ baryon lifetime is approximately 3.3 standard deviations larger than the world average value.
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Using a data sample of 980 ${rm fb}^{-1}$ of $e^+e^-$ annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we report the results of a study of excited $Xi_c$ states that decay, via the emission of photons and/or charged pions, into $Xi_c^0$ or $Xi_c^+$ ground state charmed-strange baryons. We present new measurements of the masses of all members of the $Xi_c^{prime}$, $Xi_c(2645)$, $Xi_c(2790)$, $Xi_c(2815)$, and $Xi_c(2980)$ isodoublets, measurements of the intrinsic widths of those that decay strongly, and evidence of previously unknown transitions.
Measurements on the weak decay asymmetry parameters of charmed baryon, say $Xi_c$, provide more information on the $W$-emission and $W$-exchange mechanisms controlled by the strong and weak interactions. Taking advantage of the spin polarization in the charmed baryon decays, we investigate the possibility to measure the weak decay asymmetry parameters in the $e^{+}e^{-}to Xi_c^0barXi_c^0$ process. We analyze the transverse polarization spontaneously produced in this process and spin transfer in the subsequent $Xi_c$ decays. The sensitivity to measure the asymmetry parameters are estimated for the decay $Xi_ctoXi pi$.
The $Lambda_c^+K^-$ mass spectrum is studied with a data sample of $pp$ collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 fb$^{-1}$ collected by the LHCb experiment. Three $Xi_c^0$ states are observed with a large significance and their masses and natural widths are measured to be begin{eqnarray*} m(Xi_c(2923)^0)&=& 2923.04 pm 0.25 pm 0.20 pm 0.14 ~mathrm{MeV}, Gamma(Xi_c(2923)^0) &=& 7.1 pm 0.8 pm 1.8 ~mathrm{MeV}, end{eqnarray*} begin{eqnarray*} m(Xi_c(2939)^0) &=& 2938.55 pm 0.21 pm 0.17 pm 0.14 ~mathrm{ MeV}, Gamma(Xi_c(2939)^0) &=& 10.2 pm 0.8 pm 1.1 ~mathrm{ MeV}, end{eqnarray*} begin{eqnarray*} m(Xi_c(2965)^0) &=& 2964.88 pm 0.26 pm 0.14 pm 0.14~mathrm{ MeV}, Gamma(Xi_c(2965)^0) &=& 14.1 pm 0.9 pm 1.3~mathrm{ MeV}, end{eqnarray*} where the uncertainties are statistical, systematic, and due to the limited knowledge of the $Lambda_c^+$ mass. The $Xi_c(2923)^0$ and $Xi_c(2939)^0$ baryons are new states. The $Xi_c(2965)^0$ state is in the vicinity of the known $Xi_c(2970)^0$ baryon; however, their masses and natural widths differ significantly.
We present the first measurements of the absolute branching fractions of $Xi_c^+$ decays into $Xi^- pi^+ pi^+$ and $p K^- pi^+$ final states. Our analysis is based on a data set of $(772pm 11)times 10^{6}$ $Bbar{B}$ pairs collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. We measure the absolute branching fraction of $bar{B}^{0} to bar{Lambda}_{c}^{-} Xi_{c}^{+}$ with the $Xi_c^+$ recoiling against $bar{Lambda}_c^-$ in $bar{B}^0$ decays resulting in ${cal B}(bar{B}^{0} to bar{Lambda}_{c}^{-} Xi_{c}^{+}) = [1.16 pm 0.42(rm stat.) pm 0.15(rm syst.)] times 10^{-3}$. We then measure the product branching fractions ${cal B}(bar{B}^{0} to bar{Lambda}_c^- Xi_c^+){cal B}(Xi_c^+ to Xi^- pi^+ pi^+)$ and ${cal B}(bar{B}^{0} to bar{Lambda}_c^- Xi_c^+){cal B}(Xi_c^+ to p K^- pi^+)$. Dividing these product branching fractions by $bar{B}^{0} to bar{Lambda}_{c}^{-} Xi_{c}^{+}$ yields: ${cal B}(Xi_c^+ to Xi^- pi^+ pi^+) = [2.86 pm 1.21(rm stat.) pm 0.38(rm syst.)]%$ and ${cal B}(Xi_c^+ to p K^- pi^+)=[0.45 pm 0.21(rm stat.) pm 0.07(rm syst.)]%$. Our result for ${cal B}(Xi_c^+ to Xi^- pi^+ pi^+)$ can be combined with $Xi_c^+$ branching fractions measured relative to $Xi_c^+ to Xi^- pi^+ pi^+$ to set the absolute scale for many $Xi_c^+$ branching fractions.
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