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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]
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*.C file
Lb2LcPi_def_Y0_05012014.pdf
Xib2Xi[..].pdf [30 KiB]
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Xib2XicPi_def_Y0_05012014.pdf

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]
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*.C file
CorrYieldRatio_XibOverLb_smallerPtBins.pdf

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]
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Xb_ptRatio.pdf
Xb_eta[..].pdf [13 KiB]
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Xb_etaRatio.pdf

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]
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*.C file
Lb2LcPi_LcMass.pdf
Xib2Xi[..].pdf [30 KiB]
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Xib2XicPi_XicMass.pdf

Animated gif made out of all figures.

PAPER-2014-021.gif
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thumbnail_PAPER-2014-021.gif

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]
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tex code
Table_1.pdf

Supplementary Material [file]

Supplementary material full pdf

supple[..].pdf [85 KiB]
supplementary.pdf

These 3 figures compare recent masses and lifetimes to those measured in this paper.

Fig5.pdf [13 KiB]
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Fig5.pdf
Fig6.pdf [12 KiB]
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Fig6.pdf
Fig7.pdf [13 KiB]
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*C file
Fig7.pdf

Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.