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$B$ flavour tagging using charm decays at the LHCb experiment

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Abstract

An algorithm is described for tagging the flavour content at production of neutral $B$ mesons in the LHCb experiment. The algorithm exploits the correlation of the flavour of a $B$ meson with the charge of a reconstructed secondary charm hadron from the decay of the other $b$ hadron produced in the proton-proton collision. Charm hadron candidates are identified in a number of fully or partially reconstructed Cabibbo-favoured decay modes. The algorithm is calibrated on the self-tagged decay modes $B^+ \to J/\psi \, K^+$ and $B^0 \to J/\psi \, K^{*0}$ using $3.0\mathrm{\,fb}^{-1}$ of data collected by the LHCb experiment at $pp$ centre-of-mass energies of $7\mathrm{\,TeV}$ and $8\mathrm{\,TeV}$. Its tagging power on these samples of $B \to J/\psi \, X$ decays is $(0.30 \pm 0.01 \pm 0.01) \%$.

Figures and captions

Mistag probability $\omega$ as a function of the predicted mistag probability $\eta$ for the $ B ^+\!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ data sample. A straight line fit to extract the parameters $p_0$ and $p_1$ is superimposed. The dark (green) and light (yellow) bands are the regions within $1\sigma$ and $2\sigma$ of the fitted value, respectively.

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calfit.pdf

Excess mistag probability $\Delta \omega$ as a function of the predicted mistag probability $\eta$ for the $ B ^+\!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ data sample. A straight line fit to extract the parameters $\Delta p_0$ and $\Delta p_1$ is superimposed. The dark (green) and light (yellow) bands are the regions within $1\sigma$ and $2\sigma$ of the fitted value, respectively.

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deltacalfit.pdf

Raw $ B ^0$ -- $\overline{ B }{} ^0$ mixing asymmetry (defined in Eq. 3) vs. decay-time for the $ B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0} $ data sample. The amplitude of the asymmetry is diluted due to mistagging by the charm tagger. The mixing asymmetry from the fit is superimposed.

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asymmetry.pdf

Distribution of the calibrated predicted mistag probability $\omega(\eta)$ for the $ B ^+\!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ data sample.

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etadist_bjpsik.pdf

Animated gif made out of all figures.

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Tables and captions

Decay modes used in the OS charm tagger. The symbol $H_c$ stands for any $ c $ hadron. The definition of the two right-most columns is given in the text.

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Table_1.pdf

Calibration parameters as determined from the $ B ^+\!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ and $ B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0} $ control samples. For both calibration modes, the average predicted mistag probability $\langle \eta \rangle$ is $0.379$. The first uncertainties are statistical and the second are systematic. The systematic uncertainties are evaluated using simulation.

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Tagging efficiencies ($\varepsilon_{\rm tag} $), effective mistag fractions ($\omega $), and tagging powers ($\varepsilon_{\rm eff} $) in the various data samples studied. The first uncertainties are statistical and the second are systematic. The sample labeled Simulation is the training sample of simulated $ B ^+\!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ , $ B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0} $ , and $ B ^0_ s \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \phi$ decays, which has negligible statistical uncertainties.

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Supplementary Material [file]

Supplementary material full pdf

supple[..].pdf [136 KiB]
supplementary.pdf

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2015-027. The files are: supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in various formats

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mass_b[..].pdf [37 KiB]
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mass_jpsik.pdf [26 KiB]
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Created on 18 December 2018.Citation count from INSPIRE on 18 December 2018.