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Evidence for the strangeness-changing weak decay $\Xi_b^-\to\Lambda_b^0\pi^-$

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Abstract

Using a $pp$ collision data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb detector, we present the first search for the strangeness-changing weak decay $\Xi_b^-\to\Lambda_b^0\pi^-$. No $b$ hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be ${{f_{\Xi_b^-}}\over{f_{\Lambda_b^0}}}{\cal{B}}(\Xi_b^-\to\Lambda_b^0\pi^-) = (5.7\pm1.8^{+0.8}_{-0.9})\times10^{-4}$, where $f_{\Xi_b^-}$ and $f_{\Lambda_b^0}$ are the $b\to\Xi_b^-$ and $b\to\Lambda_b^0$ fragmentation fractions, and ${\cal{B}}(\Xi_b^-\to\Lambda_b^0\pi^-)$ is the branching fraction. Assuming $f_{\Xi_b^-}/f_{\Lambda_b^0}$ is bounded between 0.1 and 0.3, the branching fraction ${\cal{B}}(\Xi_b^-\to\Lambda_b^0\pi^-)$ would lie in the range from $(0.57\pm0.21)\%$ to $(0.19\pm0.07)\%$.

Figures and captions

Invariant mass spectrum for selected $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^- $ candidates in data.

Lb2LcP[..].pdf [27 KiB]
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*.C file
Lb2LcPiMass_BDTCut.pdf

Fit to the $\delta m$ spectra in data: (top left) RS low S/B, (top right) WS low S/B, (bottom left) RS high S/B and (bottom right) WS high S/B.

Xib2Lb[..].pdf [22 KiB]
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*.C file
Xib2LbPi_RS_LoS2B_fitOpt_2_newfit_Q=BOTH_conMass.pdf
Xib2Lb[..].pdf [21 KiB]
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Xib2LbPi_WS_LoS2B_fitOpt_2_newfit_Q=BOTH_conMass.pdf
Xib2Lb[..].pdf [19 KiB]
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Xib2LbPi_RS_HiS2B_fitOpt_2_newfit_Q=BOTH_conMass.pdf
Xib2Lb[..].pdf [18 KiB]
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Xib2LbPi_WS_HiS2B_fitOpt_2_newfit_Q=BOTH_conMass.pdf

Animated gif made out of all figures.

PAPER-2015-047.gif
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thumbnail_PAPER-2015-047.gif

Tables and captions

Relative systematic uncertainties (in percent) on the signal yield determination and on the quantity $\left(f_{\Xi ^-_ b }/f_{\Lambda ^0_ b }\right)\cal{B}(\Xi ^-_ b \rightarrow \Lambda ^0_ b \pi ^- )$, as described in the text.

Table_1.pdf [50 KiB]
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tex code
Table_1.pdf

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