We report on measurements of the mass and lifetime of the Xi_b^ baryon using about 1800 Xi_b^ decays reconstructed in a protonproton collision data set corresponding to an integrated luminosity of 3.0 fb^{1} collected by the LHCb experiment. The decays are reconstructed in the Xi_b^ > Xi_c^0 pi^, Xi_c^0 > pKKpi+ channel and the mass and lifetime are measured using the Lambda_b^0 > Lambda_c^+ pi mode as a reference. We measure M(Xi_b^)  M(Lambda_b^0) = 178.36 + 0.46 + 0.16 MeV/c^2 and tau(Xi_b^)/tau(Lambda_b^0) = 1.089 + 0.026 + 0.011, where the uncertainties are statistical and systematic, respectively. These results lead to a factor of two better precision on the Xi_b^ mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations.
Invariant mass spectrum, along with the fit projections, for (left) $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^ $ and (right) $\Xi ^_ b \rightarrow \Xi ^0_ c \pi ^ $ candidates. 
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Ratio of the $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^ $ to the $\Xi ^_ b \rightarrow \Xi ^0_ c \pi ^ $ selection efficiencies as a function of decay time. The uncertainties are due to the finite size of the simulated samples. 
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Corrected yield ratio, $N_{\rm cor}(\Xi ^_ b )/N_{\rm cor}(\Lambda ^0_ b )$ in bins of decay time, along with the exponential fit. The uncertainties are statistical only. 
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Animated gif made out of all figures. 
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Fitted yields of $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^ $ and $\Xi ^_ b \rightarrow \Xi ^0_ c \pi ^ $ in each time bin. Uncertainties are statistical only. 
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Supplementary material full pdf 
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Contained are supplementary figures for LHCbPAPER2014048 Fig 4: Invariant mass spectrum for $\Xicz\to p\Km\Km\pip$ candidates that form a $\Xibm$ candidate within 80\mevcc of the $\Xibm$ fitted mass. Fig 5: Invariant mass spectrum for $\Bm\to\Dz\pim$ candidates, with $\Dz\to\Kp\Km\pip\pim$. The analysis is redone using this mode as a normalization mode to provide a crosscheck of our nominal results using the $\Lb\to\Lc\pim$ decay mode as a reference. The fitted mass difference is $M(\Xibm)M(\Bm)=518.72\pm0.51$\,(stat)\mevcc, resulting in a $\Xibm$ mass of $M(\Xibm)=5797.98\pm0.51$\,(stat) \mevcc. Fig 6: Corrected yield ratio, $N_{\rm cor}(\Xibm)/N_{\rm cor}(\Bm)$ in bins of decay time, along with the exponential fit. The uncertainties are statistical only. The fitted slope $\beta=0.0123\pm0.0172$\,(stat) ps$^{1}$. The resulting lifetime using the $\Bm$ mode for normalization is $\tau(\Xibm)=1.609\pm0.045$\,(stat). Fig. 7: Comparison of measurements of the $\Xibm$ and $\Xibz$ masses, along with this measurement. Fig 8: Comparison of measurements of the $\Xibm$ and $\Xibz$ lifetimes, along with this measurement. 
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Created on 10 July 2020.