This web page summarizes the results of the measurement of the Bc lifetime using
B_{c} -> J/ψ π based
upon approximately 6.7 fb^{-1} of data.

The results have been approved as of Aug. 4, 2011. This latest result follows the previously measured
Bc mass measurement based upon 2.4 fb^{-1} (mass measurement).

The lifetime of the B_{c} is measured using the fully-reconstructed B_{c} -> J/ψ π
decay from a data sample of 6.7 fb^{-1}. Several methods of extracting the lifetime are studied.
These methods differ in the handling and modeling of the underlying background, selection criteria, and
fitting technique. The relative agreement between these methods gives a strengthened confidence in the result.
We measure:

- τ(B
_{c}) = ( 0.452 ± 0.048 ± 0.027 ) ps - cτ(B
_{c}) = ( 136 ± 14 ± 8 ) μm

A three page powerpoint summary can be found here: .pptx .pdf.

A web page for the analysis for CDF collaborators only: web page

Below are the blessed figures.

- Figure 1: B
_{u}-> J/ψ K mass for selection 1 and selection 2 requirements for both the minimum decay time above 80 and 120 μm (.pdf) (.eps) (.gif) - Figure 2: B
_{c}-> J/ψ π mass for selection 1 and selection 2 requirements for both the minimum decay time above 80 and 120 μm (.pdf) (.eps) (.gif) - Figure 3: Sideband-subtracted J/ψ K decay time distributions relative
to the minimal selection for (top) selection 1 and (bottom) selection 2.
For selection 2, a superimposed histogram from a
function derived from Monte Carlo is
shown (solid). Also shown, is a similar Monte Carlo derived efficiency
histogram for B
_{c}-> J/ψ π (dashed). (.pdf) (.eps) (.gif) - Figure 4: Selection 1 B
_{c}-> J/ψ π sideband decay time distribution (points) with parametrized fit. (.pdf) (.eps) (.gif) - Figure 5: Selection 1 B
_{c}-> J/ψ π mass distribution after the combined mass and lifetime fit showing the various components of the fit. (.pdf) (.eps) (.gif) - Figure 6: Selection 1 B
_{c}-> J/ψ π decay time distribution after the combined mass and lifetime fit showing the various components of the fit. (.pdf) (.eps) (.gif) - Figure 7: Selection 2 B
_{c}-> J/ψ π distributions in mass and decay time superimposed with the fit showing separate signal and background components. (.pdf) (.eps) (.gif) - Figure 8: Table of the parameters of the Selection 2 B
_{c}-> J/ψ π lifetime fit. (.pdf) (.eps) (.gif) - Figure 9: The B
_{c}Monte Carlo determined effective efficiency versus decay time for the selection 2 requirements where the curve shows the fitted parametrization over the Monte Carlo points. Also shown is the parametrization shifted left (top) or right (bottom) by 20μm used to evaluate the effect on the uncertainty in the function. (.pdf) (.eps) (.gif) - Figure 10: The decay time distribution (left) for the fitted
\bc\ region in
selection 2 with a bi-linear model for the background mass
parametrization as shown (right). Shown is the projection using
the full range (old fit) over the range 6.16 to 6.60 GeV/c
^{2}. (.pdf) (.eps) (.gif) - Figure 11: Toy study showing the difference between using a bi-linear mass background mass shape and the baseline linear mass shape in extracting a lifetime from the toy. (.pdf) (.eps) (.gif)
- Figure 12: The decay time distribution for the sideband region in selection 2 with the baseline 3 exponential fit (right) and the alternate fit of 2 exponentials and a linear term (left). (.pdf) (.eps) (.gif)
- Figure 13: The residual of the fitted lifetime defined by 400 Toy MC samples where the fitted lifetime using an alternate background decay time model is compared with the baseline model divided by its statistical uncertainty. (.pdf) (.eps) (.gif)
- Figure 14: Toy Monte Carlo Decay time distributions for selection~1 (top) and for selection~2 (bottom) where multiple random trials are thrown that simulate the observed data and background. Since both distributions are consistent with no systematic shift both selection~1 and 2 are shown to be well behaved procedures for extracting the lifetime. (.pdf) (.eps) (.gif)