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

Information

LHCb-PAPER-2015-027
CERN-PH-EP-2015-193
arXiv:1507.07892 [PDF]

(Submitted on 28 Jul 2015)
JINST 10 P10005
Inspire 1385321

Tools

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.	calfit.pdf [78 KiB] HiDef png [223 KiB] Thumbnail [161 KiB] *.C file
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.	deltac[..].pdf [49 KiB] HiDef png [163 KiB] Thumbnail [134 KiB] *.C file
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.	asymmetry.pdf [54 KiB] HiDef png [113 KiB] Thumbnail [62 KiB] *.C file
Distribution of the calibrated predicted mistag probability $\omega(\eta)$ for the $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ data sample.	etadis[..].pdf [53 KiB] HiDef png [171 KiB] Thumbnail [158 KiB] *.C file
Animated gif made out of all figures.	PAPER-2015-027.gif Thumbnail

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.	Table_1.pdf [53 KiB] HiDef png [79 KiB] Thumbnail [37 KiB] tex code
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.	Table_2.pdf [44 KiB] HiDef png [27 KiB] Thumbnail [8 KiB] tex code
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.	Table_3.pdf [53 KiB] HiDef png [59 KiB] Thumbnail [29 KiB] tex code

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [136 KiB]
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	etadis[..].pdf [18 KiB] HiDef png [171 KiB] Thumbnail [161 KiB] *C file
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