Violation in the B 0 s system

One of the challenges for elementary particle physics is to trace all possible sources of the violation of CP symmetry. In the standard model, CP symmetry is violated through the CKM mechanism. Although the standard model picture of CP violation has so far been confirmed by all laboratory measurements, the level of CP violation in the standard model is too small to produce the observed baryon number density in the universe. One source of CP violation arises in the mixing of doublets of neutral mesons, as the K, composed of a down quark and a strange quark, and the B s mesons, with the down quark replaced by a bottom quark. This makes searching for CP violation in the B s decays very interesting. B hadrons are abundantly produced at the Tevatron Collider, the measured B cross section is 2.78±0.24 μb in the region of transverse momentum pT (B ) > 6.0 GeV/c and rapidity | η(B) |< 1 [1]. This cross section is three orders of magnitude larger than at ee machines running at the Υ(4S) and the available energy allows the production of the heavier B s (and Bc and Λb) hadrons, although reduced by a factor fs/fd(fu) with respect to B(B). The challenge is extracting the interesting B s signals from a level of background which is three orders of magnitude higher at production. This is achieved at CDF II and D0 with dedicated detectors, triggers and sophisticated analyses.