Search for the Rare Decays Bs(d) → &mu+&mu-
This page summarizes an analysis which searches for the rare decays Bs → μμ
and Bd → μμ . These results were finalized on
August 13th, 2009 and use a dataset of 3.7 fb-1.
This analysis supersedes the analyses performed with 2 fb-1 PRL 100,101802 (2008) (webpage), 365 pb-1 PRL 95, 221805 2005 (webpage) and 171pb-1 PRL 93, 032001 2004 (webpage).
Description
The technique used in this analysis is identical to that
described in PRL 100,101802 (2008).
The dataset is updated to include a total of 3.7 fb-1 and additional
di-muon trigger acceptance. The analysis is discussed in detail
in CDF public note 9892.
Motivation
Searches for the decays Bs → μμ
and Bd → μμ can be a powerful tool to probe for physics beyond the SM.
The SM predicts a BR( Bs → μμ ) of about 3.86x10-9.
There are various extensions to the
SM that predict an enhancement of this branching ratio by one to three orders of
magnitude. Many of these models are, presently, theoretically very interesting
since some have some relevance to the deviation of the muon (g-2),
neutrino oscillations, Bs oscillations, and dark matter/dark energy results.
As of this analysis limits are now approximately one order of magnitude above the
predicted SM branching ratio placing significant restrictions on many new physics models.
A recent paper emphasizing the connection between Bs → μμ ,
Bs oscillations and the direct detection of dark matter can be found
at hep-ph/0907.4946.
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Result: World's best limits
BR( Bs → μμ ) < 4.3x10-8 @95% CL
BR( Bd → μμ ) < 7.6x10-9 @95% CL
The signal windows (Bs in blue and Bd in red) in 3 NN bins with background fits superimposed.
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Figures
Below are gif versions of relevant figures available for download.
This analysis is divided into two
channels for events found using only the central muon system(CMU), events, and events where
one muon is found in the forward muon extension(CMX), events.
- Figure 1: Di-muon invariant mass for events satisfying preselection requirements:
gif
- Figure 2: Distributions of the input variables to the NN for B+→J/ψK normalization mode sample. Signal MC (black solid histogram) and data(blue points). The distributions are normalized to unit area: gif
- Figure 3: Distribution the NN output for dimuon sample. Signal MC (black solid histogram) and background events from data sidebands(red dashed histogram). The distributions are normalized to unit area: gif
- Figure 4: B+→J/ψK normalization mode invariant mass for events satisfying preselection requirements: gif
- Figure 5: Distributions of the input variables to the NN for dimuon sample. Signal MC (black solid histogram) and background events from data sidebands(red dashed histogram). The distributions are normalized to unit area: gif
- Figure 6: 2D Di-muon mass vs. NN output (NN>0.95) for CMU-CMU and CMU-CMX combined: gif
- Figures 7, 8 and 9: Di-muon mass (three separate NN bins) with background fits superimposed: CMU-CMU (gif ), CMU-CMX (gif) and combined (gif )
- History of Bs→μμ limits gif
- Projection of Bs →μμ expected sensitivity based on PRL 100,101802 (2008) with the current result shown: gif
