The FCNC decay of the D0 to two muons is highly suppressed in the Standard Model. The suppression results from the combination of nearly perfect GIM cancellation for charm, and helicity suppression of the muon pair. The Standard Model expectation for the branching ratio ranges from 10-19 up to 10-13 with the addition of long range effects. Such vanishingly small branching ratios are essentially unobservable.
Aside from the fact that this is a flavor changing neutral current decay, no conservation laws are violated in this decay. Therefore, New Physics which circumvents the GIM cancellation can potentially enhance the branching ratio to a measurable level, and an observation of this mode is a signal of Physics beyond the Standard Model.
|3.0×106 (dimuon)||2×1010 (ET)|
Total unlike sign dimuon events in data
|muon impact parameter||>50mm(!) for 1 track|
|muon pair DCA||<500mm||<500mm|
|C2 of the vertex fit||<50|
|Total dimuon vertices||1633||8514|
|Dimuon mass window (GeV)||1.80 - 1.92||1.56 - 2.17||1.83 - 1.90|
|DMD||± 2sD||± 1.96sD|
|Mother point back||DCA<40mm||Dq<0.9°|
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