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E. Franco

Publications and source records attributed to E. Franco.

67 records · Page 4Linked to original sources
arXiv1997

Charming-penguin enhanced B decays

Long-distance contributions of operators of the effective non-leptonic weak Hamiltonian containing charmed currents have been recently studied. Penguin-like contractions of these operators, denoted as charming penguins, have been shown to be relevant for several B decays into two pseudoscalar mesons. In particular, they are expected to give large enhancements to processes which would be otherwise Cabibbo suppressed. Their contributions easily lead to values of BR(B^+ \to K^0 π^+) and BR(B_d \to K^+ π^-) of about 1 \times 10^{-5}, as recently found by the CLEO collaboration. In this paper, we show that such large branching fractions cannot be obtained without charming penguins. This holds true irrespectively of the model used to compute the non-leptonic amplitudes and of the relevant parameters of the CKM mixing matrix. We use the experimental measurements of the B^+ \to K^0 π^+ and B_d \to K^+ π^- decay rates to constrain the charming-penguin amplitudes and to predict BRs for a large set of other two-body decay channels where their contributions are also important. These include several pseudoscalar-vector and vector-vector channels, such as B \to ρK and B \to ρK^*, which have not been measured yet.

hep-ph↗
arXiv1997

CP Violating B Decays in the Standard Model and Supersymmetry

We study the uncertainties of the Standard Model (SM) predictions for CP violating B decays and investigate where and how supersymmetric (SUSY) contributions may be disentangled. The first task is accomplished by letting the relevant matrix elements of the effective Hamiltonian vary within certain ranges. The SUSY analysis makes use of a formalism which allows to obtain model-independent results. We show that in some cases it is possible a) to measure the CP B-\bar{B} mixing phase and b) to discriminate the SM and SUSY contributions to the CP decay phases. The golden-plated decays to this purpose are the B \to ϕK_S and B \to K_S π^0 channels.

hep-ph↗
arXiv1997

Charming Penguins in B decays

Full expressions of the $B^0_d \to π^+ π^-$ and $B^0_d \to π^0 π^0$ amplitudes, given in terms of matrix elements of operators of the effective weak Hamiltonian, are used to study the dependence of the relevant branching ratios on the different contributions. The uncertainty in the extraction of the weak phase $α$ from the measurement of the time-dependent asymmetry in $B^0_d \to π^+ π^-$ decays is also analyzed. We find that, among several effects which may enhance the $B^0_d \to π^0 π^0$ branching ratio, the most important is due to ``charming penguin" diagrams that have never been studied before. These diagrams easily increase $BR(B^0_d \to π^0 π^0)$ up to a value of $1-3 \times 10^{-6}$. The same effect produces, however, a large error in the extraction of $α$ from the measurement of the $B^0_d \to π^+ π^-$ time-dependent asymmetry. We show that it is possible to determine charming-penguin amplitudes from the experimental measurement of many decay rates. Their effect is impressive in $B^+ \to π^+ K^0$ and $B^0_d \to K^+ π^-$ decays, where charming-penguin contributions easily give values of $BR(B^+ \to π^+ K^0)$ and $BR(B^0_d \to K^+ π^-)$ of about $1 \times 10^{-5}$. Among other possibilities, we also suggest to use $B^0_d \to K^0 \bar K^0$, the BR of which can be as large as $2-3 \times 10^{-6}$, to determine the size of charming-penguin amplitudes.

hep-ph↗
arXiv1996

Two-body non-leptonic decays on the lattice

We show that, under reasonable hypotheses, it is possible to study two-body non-leptonic weak decays in numerical simulations of lattice QCD. By assuming that final-state interactions are dominated by the nearby resonances and that the couplings of the resonances to the final particles are smooth functions of the external momenta, it is possible indeed to overcome the difficulties imposed by the Maiani-Testa no-go theorem and to extract the weak decay amplitudes, including their phases. Under the same assumptions, results can be obtained also for time-like form factors and quasi-elastic processes.

hep-ph↗
arXiv1995

Estimates of $ε\prime/ε$

We review the latest calculations of the next-to-leading $\DSone$ effective Hamiltonian, relevant for $K\to ππ$ transitions. Numerical results for the Wilson coefficients are given for different regularization schemes. Predictions of $\epse$, obtained using different approaches to evaluate the relevant hadronic matrix elements, are compared. Given the present value of the top mass, $m_t=(174\pm 17)$ GeV, all the analyses, in spite of the large theoretical uncertainties, indicate that the value of $\epse$ is smaller than $1\times 10^{-3}$.

hep-ph↗
arXiv1995

An Upgraded Analysis of $ε\prime/ε$ at the Next-to-Leading Order

An upgraded analysis of $\ep$, $x_d$ and $\epp/\ep$, using the latest determinations of the relevant experimental and theoretical parameters, is presented. Using the recent determination of the top quark mass, $m_t=(174 \pm 17)$ GeV, our best estimate is $\epp/\ep= 3.1 \pm 2.5 $, which lies in the range given by E731. We describe our determination of $\epp/\ep$ and make a comparison with other similar studies. A detailed discussion of the matching of the full theory to the effective Hamiltonian, written in terms of lattice operators, is also given.

hep-ph↗
arXiv1994

$b \rightarrow s γ$ AND $b \rightarrow s g$: A THEORETICAL REAPPRAISAL

We present upgraded theoretical predictions for inclusive and exclusive radiative decays of {\it B} mesons. Our results include those next-to-leading order corrections that have already been computed. Our best estimates in the Standard Model are $BR(B \rightarrow K^* γ)=(4.3 \pm 0.9^{ +1.4}_{-1.0}) \times 10^{-5}$, $BR(B \rightarrow X_s γ) =(1.9 \pm 0.2\pm 0.5) \times 10^{-4}$, $Γ(B \rightarrow K^* γ)/ Γ(B \rightarrow X_s γ)=0.23 \pm 0.09$ and $BR(B \rightarrow X_s g)= (1.57 \pm 0.15 ^{+0.86}_{-0.59} \pm 0.23) \times 10^{-3}$. We also consider limits found with two-Higgs-doublet models.

hep-ph↗
arXiv1994

Quark Masses from Lattice QCD at the Next-to-Leading Order

Using the results of several quenched lattice simulations, we predict the value of the strange and charm quark masses in the continuum at the next-to-leading order, $m^{\overline{MS}}_s(μ=2\,\, \rm{GeV})= (127 \pm 18)\,\, \rm{MeV}$ and $m^{\overline{MS}}_{ch}(μ=2 \,\,\rm{GeV})=(1.47 \pm 0.28)\,\, \rm{GeV}$. The errors quoted above have been estimated by taking into account the original statistical error of the lattice results and the uncertainties coming from the matching of the lattice to the continuum theory. A detailed presentation of the relevant formulae at the next-to-leading order and a discussion of the main sources of errors is also presented.

hep-ph↗
arXiv1993

Leading Order QCD Corrections to $b\rightarrow s \, γ$ and $b \rightarrow s \, g$ Decays in Three Regularization Schemes

We discuss in detail the calculation of the leading order QCD corrections to the Effective Hamiltonian which governs $b \rightarrow s\, γ$ and $b \rightarrow s \, g$ transitions in three different regularization schemes (HV, NDR and DRED). We show that intermediate stages of the calculation do depend on the regularization, but the same scheme independent coefficients can be obtained in all the considered schemes. A detailed discussion of the results already present in the literature is also given.

hep-ph↗
arXiv1993

Scheme Independence of the Effective Hamiltonian for $b \rightarrow s \, γ$ and $b \rightarrow s \, g$ Decays

We present a calculation of the effective weak Hamiltonian which governs $b \rightarrow s\, γ$ and $b \rightarrow s \, g$ transitions in two different renormalization schemes (NDR and HV). In the leading logarithmic approximation, we show that the coefficients of the effective Hamiltonian are scheme independent only when one takes correctly into account the scheme dependence of one- and two- loop diagrams. We demonstrate that in NDR there are contributions which were missed in previous calculations. These contributions are necessary to obtain scheme independent coefficients in the final results.

hep-ph↗
arXiv1993

The $ΔS=1$ Effective Hamiltonian Including Next-to-Leading Order QCD and QED Corrections

In this paper we present a calculation of the $ΔS=1$ effective weak Hamiltonian including next-to-leading order QCD and QED corrections. At a scale $μ$ of the order of few GeV, the Wilson coefficients of the operators are given in terms of the renormalization group evolution matrix and of the coefficients computed at a large scale $\sim M_W$. The expression of the evolution matrix is derived from the two-loop anomalous dimension matrix which governs the mixing of the relevant current-current and penguin operators, renormalized in some given regularization scheme. We have computed the anomalous dimension matrix up to and including order $\alphas^2$ and $\alphae \alphas$ in two different renormalization schemes, NDR and HV, with consistent results. We give many details on the calculation of the anomalous dimension matrix at two loops, on the determination of the Wilson coefficients at the scale $M_W$ and of their evolution from $M_W$ to $μ$. We also discuss the dependence of the Wilson coefficients/operators on the regularization scheme.

hep-ph↗
arXiv1992

$ε^{\prime}/ε$ at the next-to-leading order in QCD and QED

We present a new calculation of the CP violation parameter $ε^{\prime}/ ε$. The results reported in this paper have been obtained by using the $ΔS=1$ effective Hamiltonian computed at the next-to-leading order, including QCD and QED penguins. The matrix elements of the relevant operators have been taken from lattice QCD, at a scale $μ=2$ GeV. At this relatively large scale, the perturbative matching between the relevant operators and the corresponding coefficients is quite reliable. The effect of the next-to-leading corrections is to lower the prediction obtained at the leading order, thus favouring the experimental result of E731. We analyze different contributions to the final result and compare the leading and next-to-leading cases.

hep-ph↗