2011 QCD and High Energy Interactions - Rencontres de Moriond ...

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SM
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Figure 2: Illustration of the LHCb NP reach in B 0 s → µ + µ − resulting from the strategy proposed in Ref. [13].
LHCb, the decays must be robust with respect to the impact of NP, and the ratio of their BRs
must be theoretically well understood. These requirements are satisfied by the U-spin-related
¯B 0 s → D + s π − and ¯ B 0 d → D+ K − decays. In these channels, “factorization” of hadronic matrix
elements is expected to work very well, and the theoretical precision is limited by non-factorizable
U-spin-breaking effects, leading to an uncertainty at the few-percent level. These features can
also be tested through experimental data, supporting this picture. 14 The NP discovery potential
in B 0 s → µ + µ − at LHCb resulting from this method is illustrated in Fig. 2, which shows the
smallest value of BR(B 0 s → µ + µ − ) allowing the detection of a 5σ deviation from the SM as a
function of the luminosity at LHCb (at the nominal beam energy of 14 TeV). 13
LHCb has reported the first results for fs/fd from this strategy at this conference, 15 yielding
fs/fd = 0.245 ± 0.017|stat ± 0.018|sys ± 0.018|theo. This is an average over the data for the
¯B 0 s → D + s π − , ¯ B 0 d → D+ K − and ¯ B 0 s → D + s π − , ¯ B 0 d → D+ π − systems, where the latter offers a
variant of the method for extracting fs/fd. 14
3 Concluding Remarks
We are moving towards new frontiers in B physics. There are good chances that these studies
will reveal first footprints of NP at the LHC. Exciting years are ahead of us!
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