Observation of Bc -> J/ψ π and
mass measurement of the Bc meson
This web page summarizes the results for the observation of
Bc -> J/ψ π and
the mass measurement of the Bc meson, based
upon approximately 2.2 fb-1 of data.
The results have been approved as of July 12, 2007. This latest result is an update from previously approved 1.1 fb-1 result and
0.8 fb-1 result that are included in this update.
This result is a separate analysis from earlier work on 0.36 fb-1
This work includes that initial 0.36 fb-1 data set and additional data
collected but with a different analysis technique.
Using an unbiased selection with requirements chosen on the basis of enhancing the
reference decay, Bu -> J/ψ K, we apply those same requirements to the region of
in J/ψ π. We observe an excess of events attributed to the Bc meson with a
significance greater than 8σ. We measure the mass of the Bc meson to be:
Recent lattice QCD calculations predict :
Mass(Bc) = 6304 ± 12 +18-0 MeV/c2
- Mass(Bc) = 6274.1 ± 3.2 (stat) ± 2.6 (syst) MeV/c2
 I. F. Allison et al., Phys. Rev. Lett. 94, 172001 (2005),
A public note summarizing the analysis can be found here:
A three page powerpoint summary can be found here:
A web page for the analysis for CDF collaborators only:
Below are the eps and gif versions of all blessed figures meant for downloads.
- Figure 1: Bu mass for Opt A and Opt B selection (.ps) (.eps) (.gif)
- Figure 2: Bu mass for the full sample (.ps) (.eps) (.gif)
- Figure 3: Bc mass as data accumulates (.ps) (.eps) (.gif)
- Figure 4: Bc mass for the full sample in three mass ranges (.ps) (.eps) (.gif)
- Figure 5: Bc mass for the full sample in the extended search region (.ps) (.eps) (.gif)
- Figure 6: Bc mass with a binned fit superimposed (.ps) (.eps) (.gif)
- Figure 7: Bc mass with a binned fit and then background subtracted to count signal and background (.ps) (.eps) (.gif)
- Figure 8: ToyMC probability distribution supporting >6σ significance since our data is at S/sqrt(B)=7.5 (.ps) (.eps) (.gif)
- Figure 9: Bu mass for different 2005 run ranges (two files). File 1: (.ps) (.eps) (.gif). File 2: (.ps) (.eps) (.gif). File 3: (.ps) (.eps) (.gif).
- Figure 10: Table showing B masses for other B hadrons showing very good agreement as a cross-check (.tex) (.ps) (.gif)
- Figure 11: Bu event-by-event mass difference compared with B mass analysis supporting 0.6 MeV systematic (.ps) (.eps) (.gif)
- Figure 12: Previously blessed study of momentum scale uncertainty translating into mass uncertainty vs Q value of the decay (.ps) (.eps) (.gif)