Lessons for new physics from CKM studies

Abstract

We perform a global fit to the CKM unitarity triangle using the latest experimental and theoretical constraints. We present results for three different sets of constraints: the standard inputs used by CKMfitter and UTFit, the standard inputs minus |Vub|, and the standard inputs minus both |Vub| and |Vcb|. For the required nonperturbative weak matrix elements, we use three-flavor lattice QCD averages from www.latticeaverages.org; these have been updated to reflect all available lattice calculations as of the "End of 2010". Given current theoretical and experimental inputs, we observe an approximately 3σ tension in the CKM unitarity triangle that can be interpreted as sign of physics beyond the standard model in the flavor sector. Using a model-independent parameterization of new physics effects, we test the compatibility of new physics in kaon mixing, in B-mixing, or in B \rightarrow τ ν decay with the current data. Although the tension could be accommodated with each hypothesis, the scenarios with new physics in B-mixing or, to a lesser extent, in B \rightarrow τ ν decay are strongly preferred. Finally, we interpret these results in terms contributions to ΔS = 2 and ΔB = 2 four-fermion operators. We find that the preferred scale of new physics (with Standard Model like couplings) is in the few hundred GeV range.