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High Energy Physics - Experiment, hep-ex
MPINP:
LHCb - Abteilung Hofmann
Abstract:
First observations of the decays $\Lambda_b^0 \to \Lambda_c^+ D_{(s)}^-$ are
reported using data corresponding to an integrated luminosity of $3\,{\rm
fb}^{-1}$ collected at 7 and 8 TeV center-of-mass energy in proton-proton
collisions with the LHCb detector. In addition, the most precise measurement of
the branching fraction ${\mathcal{B}(B_s^0 \to D^+D_s^-)}$ is made and a search
is performed for the decays $B^0_{(s)} \to \Lambda_c^+ \Lambda_c^-$. The
results obtained are
\begin{eqnarray*} \mathcal{B}(\Lambda_b^0 \to \Lambda_c^+
D^-)/\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+ D_{s}^-) &=& 0.042 \pm 0.003({\rm
stat}) \pm 0.003({\rm syst}), \left[\frac{\mathcal{B}(\Lambda_b^0 \to
\Lambda_c^+ D_{s}^-)}{\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}_d^0
\to D^+D_s^-)}\right]\big/\left[\frac{\mathcal{B}(\Lambda_b^0 \to
\Lambda_c^+\pi^-)}{\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}_d^0 \to
D^+\pi^-)}\right] &=& 0.96 \pm 0.02({\rm stat}) \pm 0.06({\rm syst}),
\mathcal{B}(B_s^0 \to D^+D_s^-)/\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em
B}_d^0 \to D^+D_s^-) &=& 0.038\pm0.004({\rm stat})\pm0.003({\rm syst}),
\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}^0 \to \Lambda_c^+
\Lambda_c^-)/\mathcal{B}({\kern 0.2em}\overline{\kern -0.2em B}_d^0 \to
D^+D_s^-) & < & 0.0022\; [95\% \; {\rm C.L.}], \mathcal{B}(B^0_{s} \to
\Lambda_c^+ \Lambda_c^-)/\mathcal{B}(B_s^0 \to D^+D_s^-) & < & 0.30\; [95\% \;
{\rm C.L.}].
\end{eqnarray*} Measurement of the mass of the $\Lambda_b^0$ baryon relative
to the $B^0$ meson gives ${M(\Lambda_b^0) -M(B^0) = 339.72\pm 0.24({\rm stat})
\pm 0.18({\rm syst})}$ MeV$/c^2$. This result provides the most precise
measurement of the mass of the $\Lambda_b^0$ baryon to date.
