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Register a new userPrecision measurement of the $Xi_{cc}^{++}$ mass
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A measurement of the $Xi_{cc}^{++}$ mass is performed using data collected by the LHCb experiment between 2016 and 2018 in $pp$ collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.6 $mathrm{fb}^{-1}$. The $Xi_{cc}^{++}$ candidates are reconstructed via the decay modes $Xi_{cc}^{++}toLambda_c^+K^-pi^+pi^+$ and $Xi_{cc}^{++}toXi_c^+pi^+$. The result, $3621.55 pm 0.23{rm,(stat),} pm 0.30 {rm,(syst),}{rm MeV}/c^2$, is the most precise measurement of the $Xi_{cc}^{++}$ mass to date.
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The first measurement of the lifetime of the doubly charmed baryon $Xi_{cc}^{++}$ is presented, with the signal reconstructed in the final state $Lambda_c^+ K^- pi^+ pi^+$. The data sample used corresponds to an integrated luminosity of $1.7,mathrm{fb}^{-1}$, collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of $13mathrm{,Tekern -0.1em V}$. The $Xi_{cc}^{++}$ lifetime is measured to be $0.256,^{+0.024}_{-0.022}{,rm (stat),} pm 0.014 {,rm(syst)}mathrm{,ps}$.
A highly significant structure is observed in the $Lambda_c^+K^-pi^+pi^+$ mass spectrum, where the $Lambda_c^+$ baryon is reconstructed in the decay mode $pK^-pi^+$. The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon $Xi_{cc}^{++}$. The difference between the masses of the $Xi_{cc}^{++}$ and $Lambda_c^+$ states is measured to be $1334.94 pm 0.72 (mathrm{stat}) pm 0.27 (mathrm{syst}~mathrm{MeV}/c^2$, and the $Xi_{cc}^{++}$ mass is then determined to be $3621.40 pm 0.72 (mathrm{stat}) pm 0.27 (mathrm{syst} pm 0.14 , (Lambda_c^+)~mathrm{MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the $Lambda_c^+$ mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 $mathrm{fb}^{-1}$, and confirmed in an additional sample of data collected at 8 TeV.
A search for the doubly charmed baryon $Xi_{cc}^{+}$ is performed through its decay to the $Lambda_c^+ K^- pi^+$ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13$mathrm{,Tekern -0.1em V}$. The data correspond to a total integrated luminosity of $9,mathrm{fb}^{-1}$. No significant signal is observed in the mass range from 3.4 to 3.8$mathrm{,Gekern -0.1em V}/c^2$. Upper limits are set at $95%$ credibility level on the ratio of the $Xi_{cc}^{+}$ production cross-section times the branching fraction to that of $Lambda_c^+$ and $Xi_{cc}^{++}$ baryons. The limits are determined as functions of the $Xi_{cc}^{+}$ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15$mathrm{,Gekern -0.1em V}/c$.
The doubly charmed baryon decay $Xi_{cc}^{++} rightarrow Xi_{c}^{+} pi^{+}$ is observed for the first time, with a statistical significance of $5.9sigma$, confirming a recent observation of the baryon in the $Lambda_c^{+} K^{-} pi^{+} pi^{+}$ final state. The data sample used corresponds to an integrated luminosity of $1.7,mathrm{fb}^{-1}$, collected by the LHCb experiment in $pp$ collisions at a center-of-mass energy of $13mathrm{,Tekern -0.1em V}$. The $Xi_{cc}^{++}$ mass is measured to be begin{equation} onumber 3620.6pm 1.5~(text{stat})pm 0.4~(text{syst}) pm 0.3~(Xi_{c}^{+})~text{MeV}/it{c}^{2}, end{equation} and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be begin{equation} onumber frac{mathcal{B} (Xi_{cc}^{++} rightarrow Xi_{c}^{+} pi^{+}) times mathcal{B}(Xi_{c}^{+} rightarrow pK^{-}pi^{+})} {mathcal{B} (Xi_{cc}^{++} rightarrow Lambda_c^{+} K^{-} pi^{+} pi^{+}) times mathcal{B}(Lambda_c^{+} rightarrow pK^{-}pi^{+})} = 0.035pm 0.009~(text{stat}) pm 0.003~(text{syst}). end{equation}
We calculate the semileptonic and a subclass of sixteen nonleptonic two-body decays of the double charm baryon ground states $Xi_{cc}^{++},,Xi_{cc}^{+}$ and $Omega_{cc}^+$ where we concentrate on the nonleptonic decay modes. We identify those nonleptonic decay channels in which the decay proceeds solely via the factorizing contribution precluding a contamination from $W$-exchange. We use the covariant confined quark model previously developed by us to calculate the various helicity amplitudes which describe the dynamics of the $1/2^+ to 1/2^+$ and $1/2^+ to 3/2^+$ transitions induced by the Cabibbo favored effective $(c to s)$ and $(d to u)$ currents. We then proceed to calculate the rates of the decays as well as polarization effects and angular decay distributions of the prominent decay chains resulting from the nonleptonic decays of the double heavy charm baryon parent states.
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