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

Information

LHCb-PAPER-2019-008
CERN-EP-2019-122
arXiv:1906.08350 [PDF]

(Submitted on 19 Jun 2019)
Phys. Rev. D100 (2019) 032001
Inspire 1740743

Tools

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 [268 KiB] Thumbnail [203 KiB] *.C file
	MassPl[..].pdf [23 KiB] HiDef png [253 KiB] Thumbnail [200 KiB] *.C file
	MassPl[..].pdf [30 KiB] HiDef png [283 KiB] Thumbnail [222 KiB] *.C file
	MassPl[..].pdf [29 KiB] HiDef png [294 KiB] Thumbnail [228 KiB] *.C file
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 [197 KiB] Thumbnail [125 KiB] *.C file
	XcDeca[..].pdf [17 KiB] HiDef png [152 KiB] Thumbnail [125 KiB] *.C file
	XcDeca[..].pdf [19 KiB] HiDef png [173 KiB] Thumbnail [130 KiB] *.C file
	XcDeca[..].pdf [19 KiB] HiDef png [206 KiB] Thumbnail [135 KiB] *.C file
Animated gif made out of all figures.	PAPER-2019-008.gif Thumbnail

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 [56 KiB] HiDef png [130 KiB] Thumbnail [51 KiB] tex code
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 [75 KiB] HiDef png [122 KiB] Thumbnail [55 KiB] tex code

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [94 KiB]
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 [113 KiB] Thumbnail [71 KiB] *C file
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