cern.ch

Precision measurement of the $\Lambda_c^+$, $\Xi_c^+$ and $\Xi_c^0$ baryon lifetimes

[to restricted-access page]

Abstract

We report measurements of the lifetimes of the $\Lambda_c^+$, $\Xi_c^+$ and $\Xi_c^0$ charm baryons using proton-proton collision data at center-of-mass energies of 7 and 8\tev, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment. The charm baryons are reconstructed through the decays $\Lambda_c^+\to pK^-\pi^+$, $\Xi_c^+\to pK^-\pi^+$ and $\Xi_c^0\to pK^-K^-\pi^+$, and originate from semimuonic decays of beauty baryons. The lifetimes are measured relative to that of the $D^+$ meson, and are determined to be \begin{align*} \tau_{\Lambda_c^+} &= 203.5\pm1.0\pm1.3\pm1.4 {\rm fs}, \newline \tau_{\Xi_c^+} &= 456.8\pm3.5\pm2.9\pm3.1 {\rm fs}, \newline \tau_{\Xi_c^0} &= 154.5\pm1.7\pm1.6\pm1.0 {\rm fs}, \end{align*} where the uncertainties are statistical, systematic, and due to the uncertainty in the $D^+$ lifetime. The measurements are approximately 3--4 times more precise than the current world average values. The $\Lambda_c^+$ and $\Xi_c^+$ lifetimes are in agreement with previous measurements; however, the $\Xi_c^0$ baryon lifetime is approximately 3.3 standard deviations larger than the world average value.

Figures and captions

Invariant-mass distributions for candidate (top left) $ D ^+ $ in $B\rightarrow D ^+ \mu ^- \overline{\nu } _\mu X$, (top right) $\Lambda ^+_ c $ in $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \mu ^- \overline{\nu } _\mu X$, (bottom left) $\Xi ^+_ c $ in ${\Xi ^0_ b \rightarrow \Xi ^+_ c \mu ^- \overline{\nu } _\mu X}$, and (bottom right) $\Xi ^0_ c $ in ${\Xi ^-_ b \rightarrow \Xi ^0_ c \mu ^- \overline{\nu } _\mu X}$ candidate decays. The results of the fits, as described in the text, are overlaid.

MassPl[..].pdf [23 KiB]
HiDef png [279 KiB]
Thumbnail [204 KiB]
*.C file
MassPlot_DMu_rs_def_paper.pdf
MassPl[..].pdf [23 KiB]
HiDef png [262 KiB]
Thumbnail [200 KiB]
*.C file
MassPlot_LcMu_rs_def_paper.pdf
MassPl[..].pdf [30 KiB]
HiDef png [293 KiB]
Thumbnail [223 KiB]
*.C file
MassPlot_XicMu_rs_def_paper.pdf
MassPl[..].pdf [29 KiB]
HiDef png [299 KiB]
Thumbnail [229 KiB]
*.C file
MassPlot_XiczMu_rs_def_paper.pdf

Decay-time spectra for (top left) $ D ^+ $ signal in $B\rightarrow D ^+ \mu ^- \overline{\nu } _\mu X$, (top right) $\Lambda ^+_ c $ signal in $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \mu ^- \overline{\nu } _\mu X$, (bottom left) $\Xi ^+_ c $ signal in $\Xi ^0_ b \rightarrow \Xi ^+_ c \mu ^- \overline{\nu } _\mu X$, and (bottom right) $\Xi ^0_ c $ signal in $\Xi ^-_ b \rightarrow \Xi ^0_ c \mu ^- \overline{\nu } _\mu X$ candidate decays. Overlaid are the fit results, as described in the text, along with the uncertainties due to finite sizes of the simulated samples.

XcDeca[..].pdf [32 KiB]
HiDef png [215 KiB]
Thumbnail [126 KiB]
*.C file
XcDecaytimeFit_DMu_2012_def_paper.pdf
XcDeca[..].pdf [17 KiB]
HiDef png [154 KiB]
Thumbnail [125 KiB]
*.C file
XcDecaytimeRatioFit_LcMu_DMu_2012_tauReweight203_paper.pdf
XcDeca[..].pdf [19 KiB]
HiDef png [181 KiB]
Thumbnail [130 KiB]
*.C file
XcDecaytimeRatioFit_XicMu_DMu_2012_tauReweight455_paper.pdf
XcDeca[..].pdf [19 KiB]
HiDef png [213 KiB]
Thumbnail [136 KiB]
*.C file
XcDecaytimeRatioFit_XiczMu_DMu_2012_tauReweight155_paper.pdf

Animated gif made out of all figures.

PAPER-2019-008.gif
Thumbnail
thumbnail_PAPER-2019-008.gif

Tables and captions

Yields from the binned maximum-likelihood fits to the $H_c$ invariant mass spectra in $H_c\mu ^- $ signal candidates. For the $\Lambda ^+_ c $ and $ D ^+ $ modes, only 10% of the sample is used, since the yields in the full data set are much larger than needed in this analysis.

Table_1.pdf [42 KiB]
HiDef png [158 KiB]
Thumbnail [60 KiB]
tex code
Table_1.pdf

Summary of systematic uncertainties on the ratio of the charm baryon to $ D ^+ $ meson lifetimes (in units of $10^{-4}$). The statistical uncertainty on the measurements is also provided for reference.

Table_2.pdf [61 KiB]
HiDef png [145 KiB]
Thumbnail [67 KiB]
tex code
Table_2.pdf

Supplementary Material [file]

Supplementary material full pdf

supple[..].pdf [94 KiB]
supplementary.pdf

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2019-008. The files are: supplementary.tex supplementary.pdf, and the figures in the supplementary section invarious formats: *.pdf, *.png, *.eps.

Fig1-S.pdf [13 KiB]
HiDef png [112 KiB]
Thumbnail [71 KiB]
*C file
Fig1-S.pdf
Fig2-S.pdf [13 KiB]
HiDef png [242 KiB]
Thumbnail [110 KiB]
*C file
Fig2-S.pdf
Fig3-S.pdf [14 KiB]
HiDef png [222 KiB]
Thumbnail [112 KiB]
*C file
Fig3-S.pdf
Fig4-S.pdf [13 KiB]
HiDef png [204 KiB]
Thumbnail [97 KiB]
*C file
Fig4-S.pdf

Created on 19 October 2019.