Ricerc@Sapienza

The main goal of the experiment is to measure with an accuracy of the order of 10%, the Branching Ratio for the decay K+ -> pi+ nu nubar. This is a very clean decay mode to study flavour physics. As a matter of fact, only short-distance dynamics is relevant and, moreover, the amplitude is governed by one single semileptonic operator whose hadronic matrix element can be determined experimentally by the semileptonic kaon decay Ke3. For these reasons, this decay mode offers an unique opportunity (together with its neutral companion) to test the SM as far as the CKM matrix is concerned, complementary to B-Physics. Furthermore, the decay is very sensitive to possible new degrees of freedom beyond the SM and, due to the cleanliness of the present theoretical predictions, the measurement will lead to quite accurate constraints to any reasonable supersymmetric model.