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School of Physical and Chemical Sciences


The UTfit Collaboration is a phenomenological analysis group made up of experimentalists and theorists from various European Institutions. The main purpose of the collaboration is the extraction of fundamental parameters of the Standard Model from results obtained from all the present and past experiments and from the most updated theoretical calculations. In particular, through a global bayesian fit, the UTfit collaboration is giving the most accurate estimate of the fundamental CKM matrix parameters ρ and η. In the recent years, the B factories (BaBar and Belle) and the Tevatron experiments (CDF and D0) have produced an enormous quantity of results in the flavour sectors. These results are now effectively overconstraining the fit, allowing for both an unprecedented precision and the possibility of increasing the number of extracted parameters. The latter leads to a-posteriori predictions for various parameters within and beyond the Standard Model. As a matter of fact, we can now also add extra parameters representing generic New Physics contributions and extract them from the fit together with the CKM ones. This gives the prediction on the possible phase space allowed for a new physics contribution, taking into account all possible constraints coming from flavour physics, and it is a powerful tool also to give indication on the new physics scale.


Academic Staff

Dr Marcella Bona


 [fit results]

Standard Model

The Standard Model fit includes mainly results on the Bd results from the B factories. The basic constraints are Vub/Vcb from semileptonic B decays, Δmd and Δms from B0d,s oscillations, εK from K mixing, α from charmless hadronic B decays, γ and 2β+γ from charm hadronic B decays, and sin2β from B0 to J/ψ K0 decays. On the theoretical side, the non-perturbative QCD parameters are taken from the recent lattice QCD determinations.

New Physics fit

We perform a full analysis of the UT with all the constraints studied for the classic SM UT analysis, but reinterpreting the experimental observables including possible model-independent NP contributions. This analysis consists first in generalising the relations among the experimental observables and the elements of the CKM matrix, introducing effective model-independent parameters that quantify the deviation of the experimental results from the SM expectations. Some other constraints are also added in order to extract more information on the NP parameters. In particular, we add the following experimental inputs that are specifically thought to extract information on the NP parameters in the Bs system: the semileptonic asymmetry in Bs decays ASLs, the di-muon charge asymmetry ASLμμ, the measurement of the Bs lifetime from flavour-specific CCfinal states, the two-dimensional likelihood ratio for ΔΓs and φs=2βs-φ(Bs) from the time-dependent tagged angular analysis of Bs to J/ψφ decays.


The complete list of publications, basic references and conference talks can be found here.

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