[ Zero crossing point B0d →K*μμ = 4.9+1.1-1.3 GeV2 ]
LHCb physicists have continued their search for physics beyond the Standard Model using the B0d decay into a K* meson (an excited kaon), and a μ+ and μ–. New physics contributions can change various distributions that describe the decay process. For example, the number of decays as a function of the square of the di-muon invariant mass (q2) and the di-muon forward-backward asymmetry (AFB) can both be affected in many new physics scenarios. The variable AFB indicates whether more or fewer muons of one sign are observed in the same direction as the K* than opposite to it. The distribution of AFB in function of q2 is shown below. The results have been announced today at the Rencontres de Moriond QCD conference.
click the image for higher resolution
The point at which the AFB distribution is crossing zero is well predicted within the Standard Model, and any deviation could indicate a possible contribution from new physics. LHCb physicists have already presented at the 2011 summer conferences a first indication that the asymmetry is changing sign. Today, using three times higher statistics, they presented the first measurement of the zero-crossing point of 4.9+1.1-1.3 GeV2. This value, showed by the hatched vertical region in the Figure, is in agreement with the Standard Model prediction showed by the colored line.
The LHCb Collaboration aims to more than double its data set this year. With the new data, the zero-crossing point will be measured with higher precision, and a possible difference with the Standards Model prediction may be discovered.
Read more in the LHCb staff page.