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E. Franco

Publications and source records attributed to E. Franco.

At least 37 records · Page 2Linked to original sources
arXiv2008

Model-independent constraints on Delta F=2 operators and the scale of New Physics

We update the constraints on new-physics contributions to Delta F=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 Delta F=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 Delta F=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.

hep-ph↗
arXiv2007

D-Dbar mixing and new physics: general considerations and constraints on the MSSM

Combining the recently available 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.

hep-ph↗
arXiv2007

Improved Determination of the CKM Angle alpha from B to pi pi decays

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 constraining the value of alpha in the Standard Model. We find that the Bayesian method gives consistent results irrespective of the parametrisation 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 to pi pi decays alone the 95% probability region for alpha is the interval [80^o,170^o], well consistent with recent analyses of the unitarity triangle where, by using all the available experimental and theoretical information, one gets alpha = (93 +- 4)^o. 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.

hep-ph↗
arXiv2006

Constraints on new physics from the quark mixing unitarity triangle

The status of the Unitarity Triangle beyond the Standard Model including the most recent results on Delta m_s, on dilepton asymmetries and on width differences is presented. Even allowing for general New Physics loop contributions the Unitarity Triangle must be very close to the Standard Model result. With the new measurements from the Tevatron, we obtain for the first time a significant constraint on New Physics in the B_s sector. We present the allowed ranges of New Physics contributions to Delta F=2 processes, and of the time-dependent CP asymmetry in B_s to J/Psi phi decays.

hep-ph↗
arXiv2006

The Unitarity Triangle Fit in the Standard Model and Hadronic Parameters from Lattice QCD: A Reappraisal after the Measurements of Delta m_s and BR(B to tau nu)

The recent measurements of the B_s meson mixing amplitude by CDF and of the leptonic branching fraction BR(B to tau nu) by Belle call for an upgraded analysis of the Unitarity Triangle in the Standard Model. Besides improving the previous constraints on the parameters of the CKM matrix, these new measurements, combined with the recent determinations of the angles alpha, beta and gamma from non-leptonic decays, allow, in the Standard Model, a quite accurate extraction of the values of the hadronic matrix elements relevant for K-Kbar and B_{s,d}-B_{s,d}bar mixing and of the leptonic decay constant f_B. These values, obtained ``experimentally'', can then be compared with the theoretical predictions, mainly from lattice QCD. In this paper we upgrade the UT fit, we determine from the data the kaon B-parameter B_Khat, the B^0 mixing amplitude parameters f_Bs B^{1/2}_Bs and xi, the decay constant f_B, and make a comparison of the obtained values with lattice predictions. We also discuss the different determinations of V_ub and show that current data do not favour the value measured in inclusive decays.

hep-ph↗
arXiv2006

Next-to-leading order strong interaction corrections to the Delta F=2 effective Hamiltonian in the MSSM

We compute the next-to-leading order strong interaction corrections to gluino-mediated Delta F=2 box diagrams in the Minimal Supersymmetric Standard Model. These corrections are given by two loop diagrams which we have calculated in three different regularization schemes in the mass insertion approximation. We obtain the next-to-leading order Wilson coefficients of the Delta F=2 effective Hamiltonian relevant for neutral meson mixings. We find that the matching scale uncertainty is largely reduced at the next-to-leading order, typically from about 10-15% to few percent.

hep-ph↗
arXiv2006

The UTfit Collaboration Report on the Status of the Unitarity Triangle beyond the Standard Model I. Model-independent Analysis and Minimal Flavour Violation

Starting from a (new physics independent) tree level determination of rhobar and etabar, we perform the Unitarity Triangle analysis in general extensions of the Standard Model with arbitrary new physics contributions to loop-mediated processes. Using a simple parameterization, we determine the allowed ranges of non-standard contributions to |Delta F|=2 processes. Remarkably, the recent measurements from B factories allow us to determine with good precision the shape of the Unitarity Triangle even in the presence of new physics, and to derive stringent constraints on non-standard contributions to |Delta F|=2 processes. Since the present experimental constraints favour models with Minimal Flavour Violation, we present the determination of the Universal Unitarity Triangle that can be defined in this class of extensions of the Standard Model. Finally, we perform a combined fit of the Unitarity Triangle and of new physics contributions in Minimal Flavour Violation, reaching a sensitivity to a new physics scale of about 5 TeV. We also extrapolate all these analyses into a "year 2010" scenario for experimental and theoretical inputs in the flavour sector. All the results presented in this paper are also available at the URL http://www.utfit.org, where they are continuously updated.

hep-ph↗
arXiv2005

NLO calculation of the Delta F = 2 Hamiltonians in the MSSM and phenomenological analysis of the B - Bbar mixing

We present the NLO corrections to the Wilson coefficients of the Delta F = 2 Hamiltonians in the strong interacting sector of the MSSM, responsible for neutral meson oscillations. Such corrections, combined with the NLO anomalous dimension matrix for the Delta F = 2 operators and the corresponding hadronic matrix elements calculated on the lattice, allow for the first time a full NLO phenomenological analysis of the observables related to meson oscillations. We present preliminary results in the B_d - B_d bar sector.

hep-ph↗
arXiv2005

The 2004 UTfit Collaboration Report on the Status of the Unitarity Triangle in the Standard Model

Using the latest determinations of several theoretical and experimental parameters, we update the Unitarity Triangle analysis in the Standard Model. The basic experimental constraints come from the measurements of |V_ub/V_cb|, Delta M_d, the lower limit on Delta M_s, epsilon_k, and the measurement of the phase of the B_d - anti B_d mixing amplitude through the time-dependent CP asymmetry in B^0 to J/psi K^0 decays. In addition, we consider the direct determination of alpha, gamma, 2 beta + gamma and cos(2 beta) from the measurements of new CP-violating quantities, recently performed at the B factories. We also discuss the opportunities offered by improving the precision of the various physical quantities entering in the determination of the Unitarity Triangle parameters. The results and the plots presented in this paper can also be found at http://www.utfit.org, where they are continuously updated with the newest experimental and theoretical results.

hep-ph↗
arXiv2004

CKM-Triangle analysis: Updates and Novelties for Summer 2004

Using the most recent determinations of several theoretical and experimental parameters, we update the Unitarity Triangle analysis in the Standard Model. The basic experimental constraints come from the measurements of epsilon_k, Vub/Vcb and Delta m_d, the limit on Delta m_s, and the measurement of the CP asymmetry in the B sector through the J/psi K^0 channel. In addition we also include in our analysis the direct determination of sin 2 alpha, gamma and sin(2 beta + gamma) from the measurements of new CP-violating quantities, recently coming from the B-Factories. We also discuss the opportunities offered by improving the precision of the measurements of the various physical quantities entering in the determination of the Unitarity Triangle parameters. The results and the plots presented in this paper can be also found at http://www.utfit.org, where they are continuously updated with the newest experimental and theoretical results.

hep-ph↗
arXiv2003

The CKM Matrix and the Unitarity Triangle

This report contains the results of the Workshop on the CKM Unitarity Triangle, held at CERN on 13-16 February 2002 to study the determination of the CKM matrix from the available data of K, D, and B physics. This is a coherent document with chapters covering the determination of CKM elements from tree level decays and K and B meson mixing and the global fits of the unitarity triangle parameters. The impact of future measurements is also discussed.

hep-ph↗
arXiv2003

Lifetime Differences and CP Violation Parameters of Neutral B Mesons at the Next-to-Leading Order in QCD

We compute the next-to-leading order QCD corrections to the off-diagonal elements of the decay-width matrix Gamma entering the neutral B-meson oscillations. From this calculation the width differences DeltaGamma and the CP violation parameters (q/p) of Bd and Bs mesons are estimated, including the complete O}(alpha_s) QCD corrections and the 1/mb contributions. For the width difference DeltaGamma_s we agree with previous results. By using the lattice determinations of the relevant hadronic matrix elements we obtain the theoretical predictions DeltaGamma_d/Gamma_d=(2.42+-0.59) x 10^(-3) and DeltaGamma_s/Gamma_s=(7.4+-2.4) x 10^(-2). For the CP violation parameters, we find |(q/p)_d|-1=(2.96+-0.67) x 10^(-4) and |(q/p)_s|-1=(-1.28+-0.27) x 10^(-5). These predictions are compatible with the experimental measurements which, however, suffer at present from large uncertainties.

hep-ph↗
arXiv2003

Unitarity Triangle Analysis in the Standard Model and Sensitivity to New Physics

By using the most recent determinations of the several theoretical and experimental input parameters, we update the Unitarity Triangle analysis in the Standard Model and discuss the sensitivity to New Physics effects. We investigate the interest of measuring with a better precision the various physical quantities entering the Unitarity Triangle analysis and study in a model independent way whether, despite the undoubted success of the CKM mechanism in the Standard Model, the Unitarity Triangle analysis still allows the presence of New Physics.

hep-ph↗
arXiv2003

Worries and Hopes for SUSY in CKM Physics: The b to s Example

We discuss the twofold role of flavor and CP violation as a constraint in model building and as a signal of SUSY. Considering as an example b to s transitions, we analyze present bounds on SUSY parameters, discuss possible deviations from SM predictions in Bd and Bs physics and present strategies to reveal SUSY signals in present and future experiments in the CKM domain.

hep-ph↗
arXiv2003

b -> s Transitions: A New Frontier for Indirect SUSY Searches

The present unitarity triangle fit, whose essential input is represented by the s to d and b to d transition processes, fully agrees with the SM. However, most of the phenomena involving b to s transitions are still largely unexplored and hence b to s phenomenology still constitutes a place for new physics manifestations, in spite of the tremendous experimental and theoretical progress on B to X_s gamma. We perform a systematic study of the CP conserving and violating SUSY contributions to b to s processes in a generic MSSM. We consider gluino exchange contributions including NLO QCD corrections and lattice hadronic matrix elements for Delta B = 2 and Delta B = 1 processes. We take into account all available experimental information on processes involving b to s transitions (B to X_s gamma, B to X_s l^+ l^- and the lower bound on the B_s - bar B_s mass difference Delta M_s). We study the correlations among the relevant observables under scrutiny at present or in a not too far future: Delta M_s and the amount of CP violation in B to phi K_s, B_s to J/psi phi, B to X_s gamma. In particular we discuss the recent data by BaBar and BELLE on the time-dependent CP asymmetry in the decay B to phi K_s which suggest a deviation from the SM expectation. Our results show that the processes involving b to s transitions represent a splendid opportunity to constrain different MSSM realizations, and, even more important, that they offer concrete prospects to exhibit SUSY signals at B factories and hadron colliders in spite of all the past frustration in FCNC searches of new physics hints.

hep-ph↗
arXiv2003

b to s transitions: where to look for SUSY

We present a systematic study of the CP conserving and violating SUSY contributions to b to s processes in a generic MSSM, considering gluino exchange contributions. Experimental information on B to Xs gamma, B to Xs l+ l- and the Bs-Bsbar mass difference Delta Ms have been taken into account. We study the induced correlations among several observables: Delta Ms and the amount of CP violation in B to phi Ks, Bs to J/psi phi, B to Xs gamma. Our results show that b to s transitions represent a splendid opportunity to constrain different MSSM realizations and offer concrete prospects to exhibit SUSY signals at B factories and hadron colliders.

hep-ph↗
arXiv2002

Charming Penguins Saga

We briefly recall the main formulae for computing the B -> K pi branching ratios within the "charming penguin" approach, present an updated fit to the data, and explain why we believe that, in general, these fits can hardly be used to extract gamma.

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