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 9th, 2007 and use a dataset of 1.9 fb-1.
This analysis supersedes the analyses performed with 365 pb-1 PRL 95, 221805 2005 (webpage) and 171pb-1 PRL 93, 032001 2004 (webpage).
Description
A complete description is available at CDF Public note
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 3.8x10-9.
There are various extensions to the
SM that predict an enhancement of this branching ratio by 1 to 3 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, and dark matter/dark energy results.
Here are two plots from
Phys.Lett. B624, 47 2005 showing the excluded region
for BR( Bs → μμ ) < 2.0x10-7 @95% CL and
BR( Bs → μμ ) < 0.5x10-7 @95% CL
in the (M0,M1/2) plane for a Constrained MSSM model.
Blue regions are excluded by BR( Bs → μμ ), green regions by BR( B → s γ),
and cyan regions by relic density constraints.
A second interesting class of models that predicts enhanced rates
of Bs → μμ decay are SO(10) symmetry breaking models.
This plot from
(hep-ph/0507233) shows BR(Bs->&mu&mu)
in the (&mu,M1/2) plane. Dashed blue lines are are contours
of constant BR( Bs → μμ ), dashed black lines are are contours of constant higgs
mass, green areas are regions of parameter space consistent with the
observed relic density of dark matter and pink ares are excluded. A listing of relevant theory
papers is below.
|
Result: World's best limits
BR( Bs → μμ ) < 5.8x10-8 @95% CL
BR( Bd → μμ ) < 1.8x10-8 @95% CL
BR( Bs → μμ ) < 4.7x10-8 @90% CL
BR( Bd → μμ ) < 1.5x10-8 @90% CL
The signal windows (Bs in red and Bd in blue) for the most sensitive NN bin (NN>0.995) are shown.
|
|
Figures
Below the eps and gif versions of all figures from the public conference note available for download.
This analysis is divided into two
channels for events found using only the central muon system(CMU), U-U events, and events where
one muon is found in the forward muon extension(CMX), U-X events.
- Figure 1: B+→J/ψK Normalization mode: CMU-CMU eps gif ,
CMU-CMX eps gif ,
Combined eps gif
- Figure 2: The pT B spectrum from B+ comparing data vs re-weighted MC: eps
gif
- Figure 3: Distributions of the input variables to the NN for Bs sample. Data point (black) is signal MC with dashed histogram (red)
being background events from data sidebands. The distributions are normalized to unit area: eps
gif
- Figure 4: Di-muon invariant mass for events satisfying preselection requirements:
CMU-CMU eps gif ,
CMU-CMX eps gif
- Figure 5: Signal acceptance vs. number of background events accepted for NN with differing number of input variables: eps
- Figure 6a: Distributions of the input variables to the NN for B+ Data vs MC: eps
gif
- Figure 6b: Distributions of the input variables to the NN for B+ Data vs MC: eps
gif
- Figure 7: Combinatorial background fits to sidebands: CMU-CMU eps gif ,
CMU-CMX eps gif
- Figure 8: NeuralNet output distributions for signal and background: eps gif ,
- Figure 9: 2D Di-muon mass vs. NN output: CMU-CMU eps gif ,
CMU-CMX eps gif ,
Combined eps gif
- Figure 10: Di-muon mass for events with NN>0.995: CMU-CMU eps gif ,
CMU-CMX eps gif
- Figure 11: Di-muon mass (three separate NN bins): CMU-CMU and CMU-CMX combined eps gif
- Figure 12: History of Bs→μμ limits (no animation) jpg
- Figure 13: History of Bs→μμ limits and MSUGRA exclusion (animated) ppt gif
Experimental Papers and Status
Below is a comparison of this result to relevant experimental papers:
Theory Papers
Below are links to some relevant theory papers:
- hep-ph/0604121New Constraints on SUSY Flavour Mixing in Light of Recent Measurements at the Tevatron
(i.e. Bs Mixing and Bs → μμ)
- Phys.Lett. B538 121 2002 Detection of Bs->mu mu at the Tevatron Run II and Constraints on the SUSY Parameter Space
- JHEP 0306 054 2003 Updated Constraints on the Minimal Supergravity Model
- JHEP 0509 029 2005 Dark Matter And Bs to mu+mu- With Minimal SO(10) Soft SUSY Breaking II
- Phys.Lett. B600 261 2004 Bounding the MSSM Higgs sector from above with the Tevatron's Bs -> mu mu
- Phys.Lett. B624 47 2005 On the Interpretation of Bs -> mu mu in the CMSSM
- hep-ph/0510422 Current and Future Limits on General Flavour Violation in b-->s Transitions in Minimal Supersymmetry
- hep-ph/0603106 Constraints on B and Higgs Physics in Minimal Low Energy Supersymmetric Models
Example Feynman diagrams:
- Standard Model diagrams: Box and Penguin
- 2HDM diagrams: Box and Penguin
- SUSY diagrams: Loop
- Higgs mediated: Tree - where multiple Higgs can allow flavor violating diagrams
- R-Parity violating: Tree
