The LHCb experiment is dedicated to study CP violation processes in rare decays of B mesons. The LHC will be by far the most copious source of  B mesons, due to the high  cross section and high luminosity. A variety of  b-hadrons, such as B_u, B_d, B_s, B_c and b-baryons, are produced at high rate. The experiment will be able to uniquely identify particles by means of (RICH) Cherenkow counters, electromagnetic and hadron calorimeters and a muon  detector. A very effective trigger allows to choose both lepton and hadron final states.

Warsaw group is involved in the construction of the Outer Tracker detector. It will consist of straw drift chambers and will serve for reconstruction of charged particle tracks and their momenta measurements. Electronics engineers from the group design and build a crucial part of  the experiment data acquisition system – the Readout Supervisor.

CP violation is from its discovery in 1964 in neutral K decays one of the most basic issues in physics of elementary particles. In 1980  J.Cronin and V. Fitch obtained the Nobel prize for this discovery.

CP violation phenomena and rare decays are the important part of the Standard Model – theory describing interactions of  basic matter particles: leptons and quarks. Most of the free parameters of the Model, like masses of the quarks and Cabibbo-Kobayashi-Maskawa (CKM) matrix elements describing mixings of quark states are involved in the description of CP violation phenomena. This allows for various tests of the theory. The presence of large class  of processes described only by loop diagrams allows the tests of quantum structure of the Standard Model and provides possibility to study indirectly short distance physics, where the modifications of the SM are expected.

The interest to study CP violation is not confined to elementary particle physics. In the cosmological Standard Model the presence of the CP violation processes is one of the three necessary conditions for the asymmetry between matter and antimatter  observed in our Universe. The CP violation in the SM is, however, not sufficient to obtain the observed level of the dominance of the matter over the antimatter. The new processes are needed and they lead to the physics beyond the SM.

Until 2001 CP violation was observed only in neutral kaon states. The Standard Model can describe these observations by introducing non-zero phase in certain CKM matrix elements. The collected data are not sufficient to fully test the theory. The quantitative tests are here also limited by the unknown strong interactions effects.

In the B meson states we can find decay channels, where the strong interactions effects are either small or measured experimentally. In this case the SM provides exact predictions.  The number of decay channels is much larger than in K meson states and this allows many various tests of the SM consistency. The interesting channels have, however, usually very small branching ratios (10^-5- 10^-7). Experiments need high statistics of  B  events.

There is already the wide experimental program to study CP violation phenomena in B decays (BaBar, Belle, CDF, D0 experiments) on presently working accelerators. The available statistics of B events (~ 10⁸ per year) or detector constraints will allow, however, for only partial tests of the SM in these experiments. The dedicated detector built for LHCb experiment will fully exploit the possibilities provided by the LHC accelerator. We expect production of the order of 10¹² events with B mesons already in the first year after commissioning of the accelerator.   

In 2001 CP violation in B⁰  decays was observed for the first time in B meson factories using meson factories using e⁺e^- beams. The measured values sin 2 = 0.722 ą 0.040 ą 0.023 (BaBar) and sin 2 = 0.652 ą 0.044  (Belle) show, that the observed asymmetries are large and in agreement with the values of sin 2 obtained indirectly  from the unitary triangle. It is now clear that CP is not an approximate symmetry of the Nature and that the dominant source of the CP violation is the Kobayashi-Maskawa mechanism.

Since the construction of the LHCb detector will take few years and the LHC accelerator will be ready in 2007 it is more interesting, however, to estimate what will be the status of the CP violation studies in B decays at this time. We can expect that Belle and BaBar will collect data corresponding to 500 fb^-1 of integrated luminosity and CDF and D0 detector will use the full luminosity of the upgraded Tevatron. The main task of B physics will be the verification of the Standard Model description of CP violation provided by the CKM matrix. Optimistically we can expect that it will be possible on the level of 5 – 10 %.

The  next step will depend on the agreement of these results with the Standard Model predictions.

If it will  turn out that the full set of measurements can not be described by the CKM matrix, the main task will be the  explanation  of the observed deviations. One of the possibilities is an additional contribution from the new processes described by the loop diagrams. For instance, mixing of B⁰_d or  B⁰_s  mesons is described in the Standard Model by box diagrams with the exchange of t quarks and W bosons. In a supersymmetric extension of the SM, contribution to the mixing can come also from box diagrams with the exchange of   squarks and  winos  ( ). There are, however, other possibilities (technicolor, new quark generations, even theories with higher dimensions) and the choice will have to be made on the basis of very precise measurements.

If we will not observe any deviations from the Standard Model description, the more accurate measurements of CP violation observables will be necessary in the experiment of the next generation - LHCb . In particular, measurements of the same quantity in many various processes will be very important. Since CKM matrix is described by only four independent parameters the amplitudes in various quark transitions are correlated. If there is a contribution from New Physics, these correlations should not be observed. For instance we can measure the angle in the unitary triangle (which describes the decay phase) from decay (transition ) or from decay (transition ). In the Standard Model both amplitudes  are proportional to . The New Physics contribution can be, however, different for these two processes and the precise measurements can reveal the differences. Very important are measurements in decays when the SM predictions for the CP asymmetries are very small like in In such cases observations of asymmetries greater than few percent will be the clear sign of New Physics.