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Observation of new $Xi_c^0$ baryons decaying to $Lambda_c^+ K^-$

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 Added by Emmy Gabriel
 Publication date 2020
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and research's language is English




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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.



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We report the first observation of two charmed strange baryons that decay into $Lambda_c^+ K^-pi^+$. The broader of the two states is measured to have a mass of $2978.5pm 2.1pm 2.0$ MeV/$c^2$ and a width of $43.5pm 7.5pm 7.0$ MeV/$c^2$. The mass and width of the narrow state are measured to be $3076.7pm 0.9pm 0.5$ MeV/$c^2$ and $6.2pm 1.2pm 0.8$ MeV/$c^2$, respectively. We also perform a search for the isospin partner states that decay into $Lambda_c^+ K_S^0pi^-$ and observe a significant signal at the mass of $3082.8pm 1.8pm 1.5$ MeV/$c^2$. The data used for this analysis was accumulated at or near the $Upsilon(4S)$ resonance, using the Belle detector at the $e^+ e^-$ asymmetric-energy collider KEKB. The integrated luminosity of the data sample used is $461.5 ~mathrm{fb}^{-1}$.
The first observation of the $Omega_b^-toXi_c^+ K^- pi^-$ decay is reported using proton-proton collision data at centre-of-mass energies of $7$, $8$ and $13,mathrm{TeV}$ collected by the LHCb experiment, corresponding to an integrated luminosity of $9,mathrm{fb}^{-1}$. Four excited $Omega_c^0$ baryons are observed in the $Xi_c^+ K^-$ mass projection of the $Omega_b^-toXi_c^+ K^- pi^-$ decays with significance exceeding five standard deviations. Their relative production rates, masses and natural widths are measured, and a test of spin hypotheses is performed. Moreover, the branching ratio of $Omega_b^-toXi_c^+ K^- pi^-$ is measured relative to the $Omega_b^-to Omega_c^0 pi^-$ decay mode and a precise measurement of the $Omega_b^-$ mass of $6044.3 pm 1.2 pm 1.1^{,+0.19}_{,-0.22},mathrm{MeV}$ is obtained.
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