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An improved Standard Model prediction of BR(B →τν) and its implicationsfor New Physics

2010-02-24T23:00:00Z

An improved Standard Model prediction of BR(B →τν) and its implicationsfor New Physics Bona, Marcella; Ciuchini, Marco; Franco, Enrico; Lubicz, Vittorio; Martinelli, Guido; Parodi, Fabrizio; Pierini, Maurizio; Schiavi, Carlo; Silvestrini, Luca; Sordini, Viola; Stocchi, Achille; Tarantino, Cecilia; Vagnoni, Vincenzo 2010-02-25 Physics Letters B 687 61-69 The recently measured B →τν branching ratio allows to test the Standard Model by probing virtual effects of new heavy particles, such as a charged Higgs boson. The accuracy of the test is currently limited by the experimental error on BR(B → τν) and by the uncertainty on the parameters f B and |Vub|. The redundancy of the Unitarity Triangle fit allows to reduce the error on these parameters and thus to perform a more precise test of the Standard Model. Using the current experimental inputs, we obtain BR(B →τν)SM = (0.84±0.11)×10−4, to be compared with BR(B →τν)exp = (1.73±0.34)×10−4. The Standard Model prediction can be modified by New Physics effects in the decay amplitude as well as in the Unitarity Triangle fit. We discuss how to disentangle the two possible contributions in the case of minimal flavour violation at large tan β and generic loop-mediated New Physics. We also consider two specific models with minimal flavour violation: the Type-II Two Higgs Doublet Model and the Minimal Supersymmetric Standard Model.

Status of the Unitarity Triangle Analysis

2008-12-31T23:00:00Z

Status of the Unitarity Triangle Analysis Bona, Marcella; Ciuchini, Marco; Franco, Enrico; Lubicz, Vittorio; Martinelli, Guido; Parodi, Fabrizio; Pierini, Maurizio; Schiavi, Carlo; Silvestrini, Luca; Sordini, Viola; Stocchi, Achille; Tarantino, Cecilia; Vagnoni, Vincenzo 2009 160-163 We present an update of the Unitarity Triangle (UT) analysis, within the Standard Model (SM) and beyond. Within the SM the main novelties are the inclusion in eK of the contributions of x and fe 6= p /4 pointed out by A. J. Buras and D. Guadagnoli, and an accurate prediction of BR(B→tn), by using the indirect determination of |Vub| from the UT fit, which can be compared to the present experimental result. In the generalization of the UT analysis to investigate New Physics (NP) effects, the estimate of x is more delicate and only the effect of fe 6= p /4 has been included. We confirm an hint of NP in the Bs-¯Bs mixing at the 2.9s level, which makes a comparison with new experimental data certainly desired.

First evidence of new physics in b ↔ s transitions

2009-11-30T23:00:00Z

First evidence of new physics in b ↔ s transitions Bona, Marcella; Ciuchini, Marco; Franco, Enrico; Lubicz, Vittorio; Martinelli, Guido; Parodi, Fabrizio; Pierini, Maurizio; Schiavi, Carlo; Silvestrini, Luca; Sordini, Viola; Stocchi, Achille; Vagnoni, Vincenzo 2009-12 PMC Physics A 3 We combine all the available experimental information on Bs mixing, including the very recent tagged analyses of Bs → J/Ψϕ by the CDF and DØ collaborations. We find that the phase of the Bs mixing amplitude deviates more than 3σ from the Standard Model prediction. While no single measurement has a 3σ significance yet, all the constraints show a remarkable agreement with the combined result. This is a first evidence of physics beyond the Standard Model. This result disfavours New Physics models with Minimal Flavour Violation with the same significance.

Improved determination of the CKM Angle α from B --> π π decays

2007-06-30T22:00:00Z

Improved determination of the CKM Angle α from B --> π π decays UTfit Collaboration; Bona, M.; Ciuchini, Marco; Franco, E.; Lubicz, Vittorio; Martinelli, G.; Parodi, F.; Pierini, M.; Roudeau, P.; Schiavi, C.; Silvestrini, L.; Sordini, V.; Stocchi, A.; Vagnoni, V. 2007-07 Physical Review D 76 014015-014015-10 Motivated by a recent paper that compares the results of the analysis of the CKM angle alpha in the frequentist and in the Bayesian approaches, we have reconsidered the information on the hadronic amplitudes, which helps in constraining the value of alpha in the standard model. We find that the Bayesian method gives consistent results irrespective of the parametrization of the hadronic amplitudes and that the results of the frequentist and Bayesian approaches are equivalent when comparing meaningful probability ranges or confidence levels. We also find that from B-->pipi decays alone the 95% probability region for alpha is the interval [80°, 170°], well consistent with recent analyses of the unitarity triangle where, by using all the available experimental and theoretical information, one gets alpha=(93±4)°. Last but not least, by using simple arguments on the hadronic matrix elements, we show that the unphysical region alpha~0, present in several experimental analyses, can be eliminated.

Model-independent Constraints on ΔF=2 Operators and the Scale of New Physics

2008-02-29T23:00:00Z

Model-independent Constraints on ΔF=2 Operators and the Scale of New Physics UTfit Collaboration; Bona, M.; Ciuchini, Marco; Franco, E.; Lubicz, V.; Martinelli, G.; Parodi, F.; Pierini, M.; Roudeau, P.; Schiavi, C.; Silvestrini, L.; Sordini, V.; Stocchi, A.; Vagnoni, V. 2008-03 Journal of High Energy Physics 03 1-23 We update the constraints on new-physics contributions to ΔF = 2 processes from the generalized unitarity triangle analysis, including the most recent experimental developments. Based on these constraints, we derive upper bounds on the coefficients of the most general ΔF = 2 effective Hamiltonian. These upper bounds can be translated into lower bounds on the scale of new physics that contributes to these low-energy effective interactions. We point out that, due to the enhancement in the renormalization group evolution and in the matrix elements, the coefficients of non-standard operators are much more constrained than the coefficient of the operator present in the Standard Model. Therefore, the scale of new physics in models that generate new ΔF = 2 operators, such as next-to-minimal flavour violation, has to be much higher than the scale of minimal flavour violation, and it most probably lies beyond the reach of direct searches at the LHC.

D--Dbar Mixing and New Physics: General Considerations and Constraints on the MSSM

2007-10-31T23:00:00Z

D--Dbar Mixing and New Physics: General Considerations and Constraints on the MSSM Ciuchini, Marco; Franco, E.; Guadagnoli, D.; Lubicz, V.; Pierini, M.; Porretti, V.; Silvestrini, L. 2007-11 Physics Letters B 655 162-166 Combining the recent experimental evidence of D--Dbar mixing, we extract model-independent information on the mixing amplitude and on its CP-violating phase. Using this information, we present new constraints on the flavour structure of up-type squark mass matrices in supersymmetric extensions of the Standard Model.