Today at the International Workshop on the CKM Unitarity Triangle, CKM2014, in Vienna, Austria, the LHCb collaboration has presented the results of a measurement of the "semileptonic asymmetry", adsl.
This parameter is related to a difference in the probability of a beauty meson, B0, oscillating into its antiparticle, B0, and the probability of the reverse process. Any difference would be a manifestation of the matter-antimatter difference known as CP-violation.
The label "d" indicates decays of B0 mesons composed of b antiquarks and d quarks, while "sl" (semileptonic) indicates that leptons, in this case muons, are present among the decay products. When a B0 meson decays in this manner, the charge of the lepton determines whether it is a decay of a B0 or its antiparticle, B0. The presence of a “wrong-sign” lepton in a decay of a B0 meson indicates that a transition to a B0 meson took place before decay.
LHCb used these "wrong-sign" B0 and B0 decays in this analysis to measure adsl. The measurement is interesting because its value is predicted to be very small by the Standard Model; any significant deviation from zero could indicate a contribution of as-yet-undiscovered particles in B0 - B0 oscillations.
Today the LHCb collaboration presented the new preliminary value of adsl = (-0.02 ± 0.19 ± 0.30)% using the full 3 fb-1 2011 and 2012 data sample from the LHC. The collaboration recently published the corresponding value for the strange beauty meson B0s, composed of b antiquarks and s quarks. Using 1 fb-1 of data taken in 2011, they found assl = (-0.06 ± 0.50 ± 0.36)%. Both results indicate no CP-violation to be present within the sensitivity of the measurements and are hence are consistent with the very small values predicted by the Standard Model.
Read more: "Measurement of the semileptonic asymmetry, adsl" – LHCb