CMS-PAS-BPH-13-008 | ||

Precision lifetime measurements of b hadrons reconstructed in final states with a $\mathrm{J}/\psi\,$ meson | ||

CMS Collaboration | ||

May 2017 | ||

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Abstract:
We present measurements of the lifetimes of the $\mathrm{B^0}$, $\mathrm{B_{s}^0}$, $\Lambda^{0}_{\mathrm{b}}$, and $\mathrm{B}_\mathrm{c}^{+}$ hadrons using the decay channels $\mathrm{B}^{0}\to \mathrm{J}/\psi\, \mathrm{K}^{*}(892)^{0}$, $\mathrm{B}^{0}\to \mathrm{J}/\psi\, \mathrm{K_{S}}$, $\mathrm{B_{s}^0} \to \mathrm{J}/\psi\, \pi^{+} \pi^{-}$, $\mathrm{B_{s}^0} \to \mathrm{J}/\psi\, \phi(1020)$, $\Lambda^{0}_{\mathrm{b}} \to \mathrm{J}/\psi\, \Lambda^{0}$, and $\mathrm{B}_\mathrm{c}^{+} \to \mathrm{J}/\psi\, \pi^{+}$. The data sample, corresponding to 19.7 fb$^{-1}$, was collected from proton-proton collisions at $\sqrt{s}= $ 8 TeV using dedicated triggers to select oppositely charged muons in the $\mathrm{J}/\psi\,$ mass region. The lifetimes times the speed of light are measured to be $ c\tau_{\mathrm{B}^0} = $ 453.0 $\pm$ 1.6 (stat) $\pm$ 1.5 (syst) $\mu$m (in $\mathrm{J}/\psi\, \mathrm{K}^{*}(892)^{0}$), $ c\tau_{\mathrm{B}^0} = $ 457.8 $\pm$ 2.7 (stat) $\pm$ 2.7 (syst) $\mu$m (in $ \mathrm{J}/\psi\, \mathrm{K_{S}}$), $ c\tau_{\mathrm{B_{s}^0}} = $ 504.3 $\pm$ 10.5 (stat) $\pm$ 3.7 (syst) $\mu$m (in $ \mathrm{J}/\psi\, \pi^{+} \pi^{-}$), $ c\tau_{\mathrm{B_{s}^0}} = $ 443.9 $\pm$ 2.0 (stat) $\pm$ 1.2 (syst) $\mu$m (in $ \mathrm{J}/\psi\, \phi(1020)$), $ c\tau_{\Lambda^{0}_{\mathrm{b}}} = $ 443.1 $\pm$ 8.2 (stat) $\pm$ 2.7 (syst) $\mu$m, $ c\tau_{\mathrm{B}_\mathrm{c}^{+}} = $ 162.3 $\pm$ 8.2 (stat) $\pm$ 4.7 (syst) $\pm$ 0.1 ($\tau_{\mathrm{B}^{+}}$) $\mu$m, where the first uncertainty is statistical and the other is systematic. All results are in agreement with the current world average values. | ||

Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, EPJC 78 (2018) 457.The superseded preliminary plots can be found here. |

Figures | |

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Figure 1:
Efficiency versus $ct$ with a superimposed fit to a inverse power function for $ \mathrm{B}^{+} $ (top left), $\mathrm{B}^0 \to \mathrm{J}/\psi\, \mathrm{K}^{*0} $ (top right), $\mathrm{B}^0 \to \mathrm{J}/\psi\, \mathrm{K}_{s}^{0} $ (center left), $ \Lambda^{0}_\mathrm {b}$ (center right), $ \mathrm{B}^0_{s} \to \mathrm{J}/\psi\, \pi^{+} \pi^{-} $ (bottom left), and $ \mathrm{B}^0_{s} \to \mathrm{J}/\psi\, \phi(1020) $ (bottom right). The efficiency scale is arbitrary. |

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Figure 1-a:
Efficiency versus $ct$ with a superimposed fit to a inverse power function for $ \mathrm{B}^{+} $. The efficiency scale is arbitrary. |

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Figure 1-b:
Efficiency versus $ct$ with a superimposed fit to a inverse power function for $\mathrm{B}^0 \to \mathrm{J}/\psi\, \mathrm{K}^{*0} $. The efficiency scale is arbitrary. |

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Figure 1-c:
Efficiency versus $ct$ with a superimposed fit to a inverse power function for $\mathrm{B}^0 \to \mathrm{J}/\psi\, \mathrm{K}_{s}^{0} $. The efficiency scale is arbitrary. |

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Figure 1-d:
Efficiency versus $ct$ with a superimposed fit to a inverse power function for $ \Lambda^{0}_\mathrm {b}$. The efficiency scale is arbitrary. |

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Figure 1-e:
Efficiency versus $ct$ with a superimposed fit to a inverse power function for $ \mathrm{B}^0_{s} \to \mathrm{J}/\psi\, \pi^{+} \pi^{-} $. The efficiency scale is arbitrary. |

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Figure 1-f:
Efficiency versus $ct$ with a superimposed fit to a inverse power function for $ \mathrm{B}^0_{s} \to \mathrm{J}/\psi\, \phi(1020) $. The efficiency scale is arbitrary. |

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Figure 2:
Invariant mass (left) and $ct$ (right) distributions for $ \mathrm{B}^{+} $ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

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Figure 2-a:
Invariant mass distribution for $ \mathrm{B}^{+} $ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |

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Figure 2-b:
$ct$ distribution for $ \mathrm{B}^{+} $ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel shows the difference between the observed data and the fit divided by the data uncertainty. |

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Figure 3:
Invariant mass (left) and $ct$ (right) distributions for $ {\mathrm{B}^0 } $ candidates reconstructed from $\mathrm{J}/\psi\, \mathrm{K}^{*0} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

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Figure 3-a:
Invariant mass distribution for $ {\mathrm{B}^0 } $ candidates reconstructed from $\mathrm{J}/\psi\, \mathrm{K}^{*0} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |

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Figure 3-b:
$ct$ distribution for $ {\mathrm{B}^0 } $ candidates reconstructed from $\mathrm{J}/\psi\, \mathrm{K}^{*0} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |

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Figure 4:
Invariant mass (left) and $ct$ (right) distributions for $ {\mathrm{B}^0 } $ candidates reconstructed from $ \mathrm{J}/\psi\, \mathrm{K}_{s}^{0} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

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Figure 4-a:
Invariant mass distribution for $ {\mathrm{B}^0 } $ candidates reconstructed from $ \mathrm{J}/\psi\, \mathrm{K}_{s}^{0} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |

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Figure 4-b:
$ct$ distribution for $ {\mathrm{B}^0 } $ candidates reconstructed from $ \mathrm{J}/\psi\, \mathrm{K}_{s}^{0} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

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Figure 5:
Invariant mass (left) and $ct$ (right) distributions for $ \mathrm{B}^0_{s} $ candidates reconstructed from $\mathrm{J}/\psi\, \pi^{+} \pi^{-} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), combinatorial background (dotted), misidentified $\mathrm{B}^{+} \to \mathrm{J}/\psi\, \mathrm{K}^{+} $ background (dashed-dotted), partially reconstructed and (other) misidentified B backgrounds (vertical dashed), and the sum of signal and backgrounds (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

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Figure 5-a:
Invariant mass distribution for $ \mathrm{B}^0_{s} $ candidates reconstructed from $\mathrm{J}/\psi\, \pi^{+} \pi^{-} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), combinatorial background (dotted), misidentified $\mathrm{B}^{+} \to \mathrm{J}/\psi\, \mathrm{K}^{+} $ background (dashed-dotted), partially reconstructed and (other) misidentified B backgrounds (vertical dashed), and the sum of signal and backgrounds (solid) shown. |

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Figure 5-b:
$ct$ distribution for $ \mathrm{B}^0_{s} $ candidates reconstructed from $\mathrm{J}/\psi\, \pi^{+} \pi^{-} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), combinatorial background (dotted), misidentified $\mathrm{B}^{+} \to \mathrm{J}/\psi\, \mathrm{K}^{+} $ background (dashed-dotted), partially reconstructed and (other) misidentified B backgrounds (vertical dashed), and the sum of signal and backgrounds (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

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Figure 6:
Invariant mass (left) and $ct$ (right) distributions for $ \mathrm{B}^0_{s} $ candidates reconstructed from $\mathrm{J}/\psi\, \phi {1020} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

png pdf |
Figure 6-a:
Invariant mass distribution for $ \mathrm{B}^0_{s} $ candidates reconstructed from $\mathrm{J}/\psi\, \phi {1020} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |

png pdf |
Figure 6-b:
$ct$ distribution for $ \mathrm{B}^0_{s} $ candidates reconstructed from $\mathrm{J}/\psi\, \phi {1020} $ decays. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

png pdf |
Figure 7:
Invariant mass (left) and $ct$ (right) distributions for $\Lambda^{0}_\mathrm {b}$ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown.The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

png pdf |
Figure 7-a:
Invariant mass distribution for $\Lambda^{0}_\mathrm {b}$ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown. |

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Figure 7-b:
$ct$ distribution for $\Lambda^{0}_\mathrm {b}$ candidates. The curves are projections of the maximum-likelihood fit to the data, with the contributions from signal (dashed), background (dotted), and the sum of signal and background (solid) shown.The bottom panel of the right figure shows the difference between the observed data and the fit divided by the data uncertainty. |

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Figure 8:
The $\mathrm{J}/\psi\, \pi^{+} $ invariant mass distribution (left). The solid line represents the signal-plus-background fit. The dashed line represents the signal component, the dotted line the combinatorial background, and the dashed-dotted line the contribution from $\mathrm{B}_{c} \to \mathrm{J}/\psi\, \mathrm{K}^{+} $ decays. The $\mathrm{J}/\psi\, \mathrm{K}^{+} $ invariant mass distribution (right). The result of the fit is superimposed with a solid line. The signal is shown with a dashed line, the dotted-dashed curves represent the $\mathrm{B}^{+} \to {\mathrm{J}/\psi\, } \pi^{+} $ and $\mathrm{B}^0 $ contributions, and the dotted curve the combinatorial background. |

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Figure 8-a:
The $\mathrm{J}/\psi\, \pi^{+} $ invariant mass distribution. The solid line represents the signal-plus-background fit. The dashed line represents the signal component, the dotted line the combinatorial background, and the dashed-dotted line the contribution from $\mathrm{B}_{c} \to \mathrm{J}/\psi\, \mathrm{K}^{+} $ decays. |

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Figure 8-b:
The $\mathrm{J}/\psi\, \mathrm{K}^{+} $ invariant mass distribution. The result of the fit is superimposed with a solid line. The signal is shown with a dashed line, the dotted-dashed curves represent the $\mathrm{B}^{+} \to {\mathrm{J}/\psi\, } \pi^{+} $ and $\mathrm{B}^0 $ contributions, and the dotted curve the combinatorial background. |

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Figure 9:
The yield (left) of $\mathrm{B}_{c}^{+} \to \mathrm{J}/\psi\, \pi^{+} $ and $\mathrm{B}^{+} \to \mathrm{J}/\psi\, \mathrm{K}^{+} $ events as a function of $ct$, normalized to the bin width, as determined from fits to the invariant mass distributions. Ratio (right) of the $\mathrm{B}_{c}$ and $\mathrm{B}^{+} $ efficiency distributions as a function of ${ct} $. |

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Figure 9-a:
The yield of $\mathrm{B}_{c}^{+} \to \mathrm{J}/\psi\, \pi^{+} $ and $\mathrm{B}^{+} \to \mathrm{J}/\psi\, \mathrm{K}^{+} $ events as a function of $ct$, normalized to the bin width, as determined from fits to the invariant mass distributions. |

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Figure 9-b:
Ratio of the $\mathrm{B}_{c}$ and $\mathrm{B}^{+} $ efficiency distributions as a function of ${ct} $. |

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Figure 10:
Ratio of the efficiency-corrected ${ct}$ distributions for $\mathrm{B}_{c}$ and $\mathrm{B}^{+} $ signals. The line shows the result of fitting with an exponential function. |

Tables | |

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Table 1:
Summary of the systematic uncertainties on the lifetime measurements (in $\mu$m). The total systematic uncertainty is the sum in quadrature of all systematic sources. |

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Table 2:
Summary of the systematic uncertainties on the $\Delta \Gamma $ and $\tau _{\mathrm{B}_{c} }$ measurements. |

Summary |

The lifetime measurements of the $ \mathrm{B}^0 $, $ \mathrm{B}^0_{s} $, $\mathrm{B}_{c}$, and $\Lambda_\mathrm{b}^0$ hadrons, exploiting the decay channels $\mathrm{B}^0 \to \mathrm{J}/\psi\, \mathrm{K}^{*0}$, $\mathrm{B}^0 \to \mathrm{J}/\psi\, \mathrm{K}_{s}^{0}$, $ \mathrm{B}^0_{s} \to \mathrm{J}/\psi\, \pi^{+} \pi^{-} $, $ \mathrm{B}^0_{s} \to \mathrm{J}/\psi\, \phi$, $\Lambda_\mathrm{b}^0 \to\mathrm{J}/\psi\, \Lambda^{0}$, and $\mathrm{B}^{+} \to \mathrm{J}/\psi\, \pi^{+}$, have been presented, using proton proton collision events collected by the CMS detector at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. All measurements are in agreement with the world average values and some are at the precision of the world average of these parameters. |

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Compact Muon Solenoid LHC, CERN |