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E. Franco

Publications and source records attributed to E. Franco.

At least 55 records · Page 3Linked to original sources
arXiv2002

Lifetime Ratios of Beauty Hadrons at the Next-to-Leading Order in QCD

We compute the next-to-leading order QCD corrections to spectator effects in the lifetime ratios of beauty hadrons. With respect to previous calculations, we take into account the non vanishing value of the charm quark mass. We obtain the predictions tau(B+)/tau(Bd) = 1.06 +- 0.02, tau(Bs)/tau(Bd)= 1.00 +- 0.01 and tau(Lambdab)/tau(Bd) = 0.90 +- 0.05, in good agreement with the experimental results. In the case of tau(Bs)/tau(Bd) and tau(Lambdab)/tau(Bd), however, some contributions, which either vanish in the vacuum insertion approximation or represent a pure NLO corrections, have not been determined yet.

hep-ph↗
arXiv2002

Next-to-Leading Order QCD Corrections to Spectator Effects in Lifetimes of Beauty Hadrons

Theoretical predictions of beauty hadron lifetimes, based on the heavy quark expansion up to and including order 1/mb^2, do not to reproduce the experimental measurements of the lifetime ratios tau(B+)/tau(Bd) and tau(Lambdab)/tau(Bd). Large corrections to these predictions come from phase-space enhanced 1/mb^3 contributions, i.e. hard spectator effects. In this paper we calculate the next-to-leading order QCD corrections to the Wilson coefficients of the local operators appearing at O(1/mb^3). We find that these corrections improve the agreement with the experimental data. The lifetime ratio of charged to neutral B mesons, tau(B+)/tau(Bd), turns out to be in very good agreement with the corresponding measurement, whereas for tau(Bs)/tau(Bd) and tau(Lambdab)/tau(Bd) there is a residual difference at the 1-sigma level. We discuss, however, why the theoretical predictions are less accurate in the latter cases.

hep-ph↗
arXiv2001

B_d-Bbar_d Mixing and the B_d -> J/psi K_s Asymmetry in General SUSY Models

We present a next-to-leading order determination of the gluino-mediated SUSY contributions to B_d-Bbar_d mixing and to the CP asymmetry a_{J/psi K_s} in the framework of the mass-insertion approximation. Using hadronic matrix elements recently computed on the lattice, we obtain improved constraints on the squark-mass splittings.

hep-ph↗
arXiv2001

Two Body B Decays, Factorization and LambdaQCD/mb Corrections

By using the recent experimental measurements of B -> pi pi and B -> K pi branching ratios, we find that the amplitudes computed at the leading order of the LambdaQCD/mb expansion disagree with the observed BRs, even taking into account the uncertainties of the input parameters. Beyond the leading order, Charming and GIM penguins allow to reconcile the theoretical predictions with the data. Because of these large effects, we conclude, however, that it is not possible, with the present theoretical and experimental accuracy, to determine the CP violation angle gamma from these decays. We compare our results with those obtained with the parametrization of the chirally enhanced non-perturbative contributions by BBNS. We also predict large asymmetries for several of the particle--antiparticle BRs, in particular BR(B+ -> K+ pi0), BR(Bd -> K+ pi-) and BR(Bd -> pi+ pi-).

hep-ph↗
arXiv2001

Charming Penguins Strike Back

By using the recent experimental measurements of B to pi pi and B to K pi branching ratios, we find that factorization is unable to reproduce the observed BRs even taking into account the uncertainties of the input parameters. Charming and GIM penguins allow to reconcile the theoretical predictions with the data. Because of these large effects, we conclude, however, that it is not possible, with the present theoretical and experimental accuracy, to determine the CP violation angle gamma from these decays. Contrary to factorization, we predict large asymmetries for several of the particle-antiparticle BRs, in particular BR(B^+ to K^+ pi^0), BR(B_d to K^+ pi^-) and BR(B_d to pi^+ pi^-). This opens new perspectives for the study of CP violation in B systems.

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arXiv2001

Penguin Contractions and Factorization in B -> K pi Decays

We study Lambda_{QCD}/m_B corrections to factorization in B -> K pi decays. First, we analyze these decay channels within factorization, showing that, irrespectively of the value of gamma, it is not possible to reproduce the experimental data. Then, we discuss Lambda_{QCD}/m_B corrections to these processes, and argue that there is a class of doubly Cabibbo enhanced non-factorizable contributions, usually called charming penguins, that cannot be neglected. Including these corrections, we obtain an excellent agreement with experimental data. Furthermore, contrary to what is obtained with factorization, we predict sizable rate asymmetries in B^\pm -> K^\pm π^0 and B -> K^\pm pi^\mp.

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arXiv2001

2000 CKM-Triangle Analysis A Critical Review with Updated Experimental Inputs and Theoretical Parameters

Within the Standard Model, a review of the current determination of the sides and angles of the CKM unitarity triangle is presented, using experimental constraints from the measurements of |ε_K|, |V_{ub}/V_{cb}|, Δm_d and from the limit on Δm_s, available in September 2000. Results from the experimental search for {B}^0_s-\bar{B}^0_s oscillations are introduced in the present analysis using the likelihood. Special attention is devoted to the determination of the theoretical uncertainties. The purpose of the analysis is to infer regions where the parameters of interest lie with given probabilities. The BaBar "95 %, C.L. scanning" method is also commented.

hep-ph↗
arXiv2000

Delta M_K and epsilon_K in SUSY at the Next-to-Leading order

We perform a Next-to-Leading order analysis of Delta S=2 processes beyond the Standard Model. Combining the recently computed NLO anomalous dimensions and the B parameters of the most general Delta S=2 effective Hamiltonian, we give an analytic formula for Delta M_K and epsilon_K in terms of the Wilson coefficients at the high energy scale. This expression can be used for any extension of the Standard Model with new heavy particles. Using this result, we consider gluino-mediated contributions to Delta S=2 transitions in general SUSY models and provide an improved analysis of the constraints on off-diagonal mass terms between the first two generations of down-type squarks. Finally, we improve the constraints on R-violating couplings from Delta M_K and epsilon_K.

hep-ph↗
arXiv2000

Final State Interactions and epsilon'/epsilon: A Critical Look

We critically analyze recent attempts to include final state interaction (FSI) effects in the calculation of the CP violating ratio epsilon'/epsilon. In particular the approach of using the Muskhelishvili-Omnes equation for the decay amplitudes is examined. We find that the values of the dispersive correction factors are very sensitive to initial conditions which are, at present, out of control, and demonstrate that the claimed large enhancement of epsilon'/epsilon through FSI is questionable. We propose, instead, a different implementation of this approach which may be useful to lattice determinations of weak amplitudes.

hep-ph↗
arXiv1999

Epsilon'/epsilon from Lattice QCD

Lattice calculations of matrix elements relevant for kaon decays, and in particular for epsilon'/epsilon, are reviewed. The role of the strange quark mass is also discussed. A comparison with other non-perturbative approaches used to compute kaon decay amplitudes is made.

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arXiv1999

Combined analysis of the unitarity triangle and CP violation in the Standard Model

We perform a combined analysis of the unitarity triangle and of the CP violating parameter epsilon'/epsilon using the most recent determination of the relevant experimental data and, whenever possible, hadronic matrix elements from lattice QCD. We discuss the role of the main non-perturbative parameters and make a comparison with other recent analyses. We use lattice results for the matrix element of Q_8 obtained without reference to the strange quark mass. Since a reliable lattice determination of the matrix element of Q_6 is still missing, the theoretical predictions for epsilon'/epsilon suffer from large uncertainties. By evaluating this matrix element with the vacuum-saturation approximation, we typically find as central value epsilon'/epsilon = (4 - 7) x 10^(-4). We conclude that the experimental data suggest large deviation of the value of the matrix element of Q_6 from the vacuum-saturation approximation, possibly due to penguin contractions.

hep-ph↗
arXiv1998

Heavy-heavy form factors and generalized factorization

We reanalyze B -> D pi and B -> K J/psi data to extract a set of parameters which give the relevant hadronic matrix elements in terms of factorized amplitudes. Various sources of theoretical uncertainties are studied, in particular those depending on the model adopted for the form factors. We find that the fit to the B -> D pi branching ratios substantially depends on the model describing the Isgur-Wise function and on the value of its slope. This dependence can be reduced by substituting the BR(B -> D pi) with suitable ratios of non-leptonic to differential semileptonic BRs. In this way, we obtain a model-independent determination of these parameters. Using these results, the B -> D form factors at q^2=M_pi^2 can be extracted from a fit of the BR(B -> D pi). The comparison between the form factors obtained in this way and the corresponding measurements in semileptonic decays can be used as a test of (generalized) factorization free from the uncertainties due to heavy-heavy form factor modeling. Finally, we present predictions for yet-unmeasured D pi and D K branching ratios and extract f_{D_s} and f_{D_s^*} from B -> DD_s decays. We find f_{D_s} = 270 +- 45 MeV and f_{D_s^*}=260 +- 40 MeV, in good agreement with recent measurements and lattice calculations.

hep-ph↗
arXiv1998

Model independent determination of the light-cone wave functions for exclusive processes

We present a method to compute, by numerical simulations of lattice QCD, the light-cone wave functions which enter exclusive processes at large momentum transfer, such as electromagnetic elastic scatterings, or exclusive semi-leptonic decays as B -> pi (B -> rho) and radiative decays as B -> K* gamma. The method is based on first principles and does not require any model assumption.

hep-ph↗
arXiv1998

Model independent determination of the shape function for inclusive B decays and of the structure functions in DIS

We present a method to compute, by numerical simulations of lattice QCD, the inclusive semileptonic differential decay rates of heavy hadrons and the structure functions which occur in deep inelastic scattering. The method is based on first principles and does not require any model assumption. It allows the prediction of the differential rate in B semileptonic decays for values of the recoiling hadronic mass W ~ sqrt(M_B Lambda_QCD), which is in the relevant region to extract |V_ub| from the end-point of the lepton spectrum in inclusive decays.

hep-ph↗
arXiv1998

Quark Mass Renormalization in the $\MSbar$ and RI schemes up to the NNLO order

We compute the relation between the quark mass defined in the minimal modified $\MSbar$ scheme and the mass defined in the ``Regularization Invariant" scheme (RI), up to the NNLO order. The RI scheme is conveniently adopted in lattice QCD calculations of the quark mass, since the relevant renormalization constants in this scheme can be evaluated in a non-perturbative way. The NNLO contribution to the conversion factor between the quark mass in the two schemes is found to be large, typically of the same order of the NLO correction at a scale $μ\sim 2$ GeV. We also give the NNLO relation between the quark mass in the RI scheme and the renormalization group-invariant mass.

hep-ph↗
arXiv1997

Next-to-Leading Order QCD Corrections to $ΔF =2$ effective Hamiltonians

The most general QCD next-to-leading anomalous-dimension matrix of all possible four-fermion, dimension-six $ΔF=2$ operators is computed. The results of this calculation can be used in many phenomenological applications, among which the most important are those related to theoretical predictions of $K^0-\bar{K}^0 $ and $B^0-\bar{B}^0$ mixing in several extension of the Standard Model (Supersymmetry, left-right symmetric, multi-Higgs models, etc.), to estimates of the $B^0_s$--$\bar B^0_s$ width difference, $ΔΓ_{B_s}$, and to the calculation of the $O(1/m_b^3)$ corrections for inclusive b-hadron decay rates.

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