# Precision measurement of the mass and lifetime of the $\Xi_b^0$ baryon

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## Abstract

Using a proton-proton collision data sample corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at center-of-mass energies of 7 and 8 TeV, about 3800 $\Xi_b^0\to\Xi_c^+\pi^-$, $\Xi_c^+\to pK^-\pi^+$ signal decays are reconstructed. From this sample, the first measurement of the $\Xi_b^0$ baryon lifetime is made, relative to that of the $\Lambda_b^0$ baryon. The mass differences $M(\Xi_b^0)-M(\Lambda_b^0)$ and $M(\Xi_c^+)-M(\Lambda_c^+)$ are also measured with precision more than four times better than the current world averages. The resulting values are $\frac{\tau_{\Xi_b^0}}{\tau_{\Lambda_b^0}} = 1.006\pm0.018\pm0.010$, $M(\Xi_b^0) - M(\Lambda_b^0) = 172.44\pm0.39\pm0.17 MeV/c^2$, $M(\Xi_c^+) - M(\Lambda_c^+) = 181.51\pm0.14\pm0.10 MeV/c^2$, where the first uncertainty is statistical and the second is systematic. The relative rate of $\Xi_b^0$ to $\Lambda_b^0$ baryon production is measured to be $\frac{f_{\Xi_b^0}}{f_{\Lambda_b^0}}\frac{{\cal{B}}(\Xi_b^0\to\Xi_c^+\pi^-)}{{\cal{B}}(\Lambda_b^0\to\Lambda_c^+\pi^-)}\frac{{\cal{B}}(\Xi_c^+\to pK^-\pi^+)}{{\cal{B}}(\Lambda_c^+\to pK^-\pi^+)} = (1.88\pm0.04\pm0.03)\times10^{-2}$, where the first factor is the ratio of fragmentation fractions, $b\to\Xi_b^0$ relative to $b\to\Lambda_b^0$. Relative production rates as functions of transverse momentum and pseudorapidity are also presented.

## Figures and captions

 Invariant mass spectrum for (left) $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^-$ and (right) $\Xi ^0_ b \rightarrow \Xi^+_ c \pi ^-$ candidates along with the projections of the fit. Lb2LcP[..].pdf [22 KiB] HiDef png [322 KiB] Thumbnail [238 KiB] *.C file Xib2Xi[..].pdf [30 KiB] HiDef png [320 KiB] Thumbnail [226 KiB] *.C file Efficiency-corrected yield ratio of $\Xi ^0_ b \rightarrow \Xi^+_ c \pi ^-$ relative to $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^-$ decays in bins of decay time. A fit using an exponential function is shown. The uncertainties are statistical only. CorrYi[..].pdf [14 KiB] HiDef png [61 KiB] Thumbnail [45 KiB] *.C file Efficiency-corrected yield ratio of $\Xi ^0_ b \rightarrow \Xi^+_ c \pi ^-$ relative to $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^-$ decays as functions of (left) $p_{\rm T}$ and (right) pseudorapidity, $\eta$. The points are positioned along the horizontal axis at the weighted average value within each bin. The uncertainties are statistical only. Xb_ptRatio.pdf [13 KiB] HiDef png [79 KiB] Thumbnail [67 KiB] *.C file Xb_eta[..].pdf [13 KiB] HiDef png [76 KiB] Thumbnail [69 KiB] *.C file Distributions of the $p K ^- \pi ^+$ invariant mass for (left) $\Lambda ^+_ c$ and (right) $\Xi^+_ c$ candidates along with the projections of the fit. Lb2LcP[..].pdf [29 KiB] HiDef png [218 KiB] Thumbnail [168 KiB] *.C file Xib2Xi[..].pdf [30 KiB] HiDef png [308 KiB] Thumbnail [219 KiB] *.C file Animated gif made out of all figures. PAPER-2014-021.gif Thumbnail

## Tables and captions

 Summary of systematic uncertainties on the reported measurements. Below, PR represents the relative uncertainty on the production ratio measurement. Table_1.pdf [64 KiB] HiDef png [85 KiB] Thumbnail [41 KiB] tex code

## Supplementary Material [file]

 Supplementary material full pdf supple[..].pdf [85 KiB] These 3 figures compare recent masses and lifetimes to those measured in this paper. Fig5.pdf [13 KiB] HiDef png [84 KiB] Thumbnail [73 KiB] *C file Fig6.pdf [12 KiB] HiDef png [82 KiB] Thumbnail [70 KiB] *C file Fig7.pdf [13 KiB] HiDef png [62 KiB] Thumbnail [52 KiB] *C file

Created on 16 August 2019.Citation count from INSPIRE on 20 August 2019.