Marco Ciuchini

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 a 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 ∼ MW. 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 αs2 and αeαs 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 MW and of their evolution from MW to μ. We also discuss the dependence of the Wilson coefficients/operators on the regularization scheme.

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 |?k|, |Vub/Vcb|, ?md and from the limit on ?ms, available in September 2000. Results from the experimental search for B0s?0s 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.

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 |Vub/Vcb|, Δmd, the lower limit on Δms, K, and the measurement of the phase of the Bd–d mixing amplitude through the time-dependent CP asymmetry in B0→J/ψK0 decays. In addition, we consider the direct determination of α, γ, 2β+γ and cos 2β 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 the URL http://www.utfit.org , where they are continuously updated with the newest experimental and theoretical results.

Electroweak precision observables, new physics and the nature of a 126 GeV Higgs boson

A bstractWe perform the fit of electroweak precision observables within the Standard Model with a 126 GeV Higgs boson, compare the results with the theoretical predictions and discuss the impact of recent experimental and theoretical improvements. We introduce New Physics contributions in a model-independent way and fit for the S, T and U parameters, for the ϵ1,2,3,b ones, for modified

First evidence of new physics in b ↔ s transitions

Zb\overline{b}

Scheme independence of the effective Hamiltonian for b → sγ and b → sg decays

couplings and for a modified Higgs coupling to vector bosons. We point out that composite Higgs models are very strongly constrained. Finally, we compute the bounds on dimension-six operators relevant for the electroweak fit.

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

We combine all the available experimental information on Bsmixing, including the very recent tagged analyses of Bs→ J/Ψϕ by the CDF and DØ collaborations. We find that the phase of the Bsmixing 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.PACS Codes: 12.15.Ff, 12.15.Hh, 14.40.Nb

B → K∗ ℓ + ℓ − decays at large recoil in the Standard Model: a theoretical reappraisal

We present a calculation of the effective weak Hamiltonian which governs b → sγ and b → sg 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.

Charming penguins strike back

Abstract We present a next-to-leading order determination of the gluino-mediated SUSY contributions to B d – B d mixing and to the CP asymmetry a J / ψK 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.

Lifetime differences and CP violation parameters of neutral B mesons at the next-to-leading order in QCD

A bstractWe critically reassess the theoretical uncertainties in the Standard Model calculation of the B → K∗ℓ+ℓ− observables, focusing on the low q2 region. We point out that even optimized observables are affected by sizable uncertainties, since hadronic contributions generated by current-current operators with charm are difficult to estimate, especially for q2 ∼ 4mc2 ≃ 6.8 GeV2. We perform a detailed numerical analysis and present both predictions and results from the fit obtained using most recent data. We find that non-factorizable power corrections of the expected order of magnitude are sufficient to give a good description of current experimental data within the Standard Model. We discuss in detail the q2 dependence of the corrections and their possible interpretation as shifts of the Standard Model Wilson coefficients.