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E. Lunghi

Publications and source records attributed to E. Lunghi.

At least 37 records · Page 2Linked to original sources
arXiv2010

Flavor Physics in the Quark Sector

One of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor and measurements and theoretical interpretations of their results have advanced tremendously: apart from masses and quantum numbers of flavor particles, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. Till early 1990s observations of CP violation were confined to neutral $K$ mesons, but since then a large number of CP-violating processes have been studied in detail in neutral $B$ mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of $K, D$, and $B$ mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model. In the near future, there will be a transition from the current to a new generation of experiments, thus a review of the status of quark flavor physics is timely. This report summarizes the results of the current generation of experiments that is about to be completed and it confronts these results with the theoretical understanding of the field.

hep-ph↗
arXiv2009

Unitarity Triangle Without Semileptonic Decays

Use of semi-leptonic decays has become standard in constraining the Unitarity Triangle. Bearing in mind that precise calculations of these are very challenging, we propose an entirely new approach. In particular the |Vcb| + epsilon_K constraint, which depends extremely sensitively on Vcb in the traditional method, is replaced by the interplay between epsilon_K, BR(B ->tau nu) and Delta M_Bs. It is found that even in this method tensions with the Standard Model persist at the ~1.8 sigma level. Furthermore, improvements on the B -> tau nu branching ratio and on the lattice determination of f_Bs Bs^(1/2) can increase the effectiveness of this method significantly.

hep-ph↗
arXiv2009

Hints for the scale of new CP-violating physics from B-CP anomalies

We consider several hints for new physics involving CP-asymmetries in B-decays and interpret them in terms of generic contributions to effective Wilson coefficients. The effects we focus on are: the differences in the fitted value of sin(2 beta) versus the ones directly measured via the time dependent CP asymmetries in B -> J/psi K or via B -> (phi,eta') K; the difference between the direct CP asymmetries in B- -> K- pi0 and B0 -> K- pi+ and the ~2.2 sigma indications for the CP-asymmetry in Bs -> J/psi phi. To alleviate concerns regarding the disagreement between inclusive and exclusive Vub, we show that our results hold even without the inclusion of Vub in the analysis. We find that no matter what kind of new physics (NP) is invoked to explain these effects, its effective scale is bounded from above from a few hundred GeV to a few TeV depending on specific assumptions regarding the type of new physics. The only exception to this is when the NP contribution is assumed to reside entirely in LR operators in K mixing, then the scale of NP can be as high as around 24 TeV; however, this case cannot account for CP asymmetry in Bs -> J/psi phi or a difference in sin(2 beta) from penguin modes compared to that from J/psi K or for that matter the large difference seen between direct CP asymmetries in K- pi+ and in K- pi0.

hep-ph↗
arXiv2008

The Role of Collinear Photons in the Rare Decay anti-B --> X(s) l+ l-

We review the phenomenology of the rare decay \bar B -> X_s l+ l-. We present the results of a detailed phenomenological analysis and discuss the role of the decay in the search for new physics at present and future colliders. Moreover, we extensively elaborate on the size of electromagnetic logarithms ln(m_b^2/m_l^2) in view of experimental cuts. We point out the differences in the analyses of BaBar and Belle and give suggestions on how to treat collinear photons in the experimental analyses. These recommendations correspond precisely to theoretical prescriptions and can be combined with measurements performed at a Super-B factory.

hep-ph↗
arXiv2007

Huge right-handed current effects in B->K*(K pi)l+l- in supersymmetry

Transverse asymmetries in the decay B->K*(K pi)l+l- are an extremely sensitive probe of right-handed flavour-changing neutral currents. We show how to include the contribution from the chiral partner of the electromagnetic operator on the transverse asymmetries at NLO in QCD factorization. We then consider supersymmetric models with non-minimal flavour violation in the down-squark sector. We include all the relevant experimental constraints and present a numerical formula for B->Xs gamma that takes into account the most recent NNLO calculations. We show that the flavour-changing parameters of these models are poorly constrained by present data and allow for large effects on the transverse asymmetries that we consider.

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arXiv2005

Untagged B -> X_(s+d) gamma CP asymmetry as a probe for new physics

The direct CP asymmetry in the untagged inclusive channel B -> X_(s+d) gamma provides a strict test of the standard model. It has been shown beyond the partonic level that this asymmetry is negligibly small thanks to U-spin relations and to the unitarity of the CKM matrix. In the present paper we investigate this relation beyond the SM; in particular, we analyse to which extent deviations from this prediction are possible in supersymmetric scenarios. We analyse the minimal flavour violation scenario, including tan(beta) enhanced terms and using the complete two-loop renormalization group running. Our analysis fully takes into account also the EDM constraints on the supersymmetric phases. We investigate possible correlations between the tagged and the untagged CP asymmetries and the indirect sensitivity of the latter to the B -> X_d gamma CP asymmetry. Furthermore, we derive general model-independent formulae for the branching ratios and CP asymmetries for the inclusive B -> X_d gamma and B -> X_s gamma modes, and update the corresponding SM predictions.

hep-ph↗
arXiv2005

The Discovery Potential of a Super B Factory

The Proceedings of the 2003 SLAC Workshops on flavor physics with a high luminosity asymmetric e+e- collider. The sensitivity of flavor physics to physics beyond the Standard Model is addressed in detail, in the context of the improvement of experimental measurements and theoretical calculations.

hep-ph↗
arXiv2004

Reducing the Error on alpha in B-> pi pi, rho rho, rho pi

Theoretical errors in the extraction of alpha from B -> pi^+ pi^-, rho^+ rho^-, rho pi decays are usually given in terms of upper bounds on alpha_eff-alpha obtained from isospin or from SU(3) relations, where alpha_eff is measured through CP asymmetries. We show that mild assumptions about magnitudes and strong phases of penguin and tree amplitudes (|P/T| < 1 and |delta| < pi/2) in B -> pi pi and B -> rho rho, imply alpha_eff > alpha, thus reducing by a factor two the error in alpha. Similarly, the assumptions |p_+-/t_+-| < 1, |δ_-| < pi/2 <|δ_+| in B -> rho pi lead to a cancellation between two terms in alpha_eff-alpha. Current data support these conditions.

hep-ph↗
arXiv2004

Implication of the $B \to (ρ, ω) γ$ Branching Ratios for the CKM Phenomenology

We study the implication of the recent measurement by the BELLE collaboration of the averaged branching fraction $\bar B_{exp} [B \to (ρ, ω) γ] = (1.8^{+0.6}_{-0.5} \pm 0.1) \times 10^{-6}$ for the CKM phenomenology. Combined with the averaged branching fraction $\bar B_{exp} (B \to K^* γ) = (4.06 \pm 0.26) \times 10^{-5}$ measured earlier, this yields $\bar R_{exp} [(ρ, ω) γ/K^* γ] = (4.2 \pm 1.3)%$ for the ratio of the two branching fractions. Updating earlier theoretical analysis of these decays based on the QCD factorization framework, and constraining the CKM-Wolfenstein parameters from the unitarity fits, our results yield $\bar B_{th} [B \to (ρ, ω) γ] = (1.38 \pm 0.42) \times 10^{-6}$ and $\bar R_{th} [(ρ, ω) γ/K^* γ] = (3.3 \pm 1.0)%$, in agreement with the BELLE data. Leaving instead the CKM-Wolfenstein parameters free, our analysis gives (at 68% C.L.) $0.16\leq |V_{td}/V_{ts}| \leq 0.29$, which is in agreement with but less precise than the indirect CKM-unitarity fit of the same, $0.18 \leq |V_{td}/V_{ts}| \leq 0.22$. The isospin-violating ratio in the $B \to ργ$ decays and the SU(3)-violating ratio in the $B_d^0 \to (ρ^0, ω) γ$ decays are presented together with estimates of the direct and mixing-induced CP-asymmetries in the $B \to (ρ,ω) γ$ decays within the SM. Their measurements will overconstrain the angle $α$ of the CKM-unitarity triangle.

hep-ph↗
arXiv2002

Improved Model-Independent Analysis of Semileptonic and Radiative Rare Decays

We study the impact of recent B-factories measurements and upper limit of radiative and semileptonic rare B-decays. We present model independent constraints on the relevant Wilson coefficients and show the impact on the parameter space of some concrete realizations of the Minimal Supersymmetric Standard Model.

hep-ph↗
arXiv2002

NNLO Analysis Of Semileptonic Rare B Decays

We update the standard model predictions for the branching ratios of the decays B -> (K,K*,Xs) l^+ l^-, with l=e,mu. Using the measurements of BR(B -> Xs gamma) and BR(B -> K l^+ l^-) as well as the upper limits on BR(B -> (K*,Xs) l^+ l^-)$, we work out model independent bounds on the relevant Wilson coefficients. We show the impact of such bounds on the parameter space of the MSSM with minimal flavour violation and of supersymmetric models with additional sources of flavour changing.

hep-ph↗
arXiv2002

Improved Model-Independent Analysis of Semileptonic and Radiative Rare B Decays

We update the branching ratios for the inclusive decays $B\to X_s \ell^+ \ell^-$ and the exclusive decays $B\to (K,K^*) \ell^+ \ell^-$, with $\ell=e, \m$, in the standard model by including the explicit $O(\a_s)$ and $Λ_{\hbox{\tiny QCD}} / m_b$ corrections. This framework is used in conjunction with the current measurements of the branching ratios for $B\to X_s \g$ and $B\to K \ell^+ \ell^-$ decays and upper limits on the branching ratios for the decays $B\to (K^*,X_s) \ell^+ \ell^-$ to work out bounds on the Wilson coefficients $C_7$, $C_8$, $C_9$ and $C_{10}$ appearing in the effective Hamiltonian formalism. The resulting bounds are found to be consistent with the predictions of the standard model and some variants of supersymmetric theories. We illustrate the constraints on supersymmetric parameters that the current data on rare B decays implies in the context of minimal flavor violating model and in more general scenarios admitting additional flavor changing mechanisms. Precise measurements of the dilepton invariant mass distributions in the decays $B \to (X_s,K^*,K) \ell^+ \ell^-$, in particular in the lower dilepton mass region, and the forward-backward asymmetry in the decays $B \to (X_s,K^*) \ell^+ \ell^-$, will greatly help in discriminating among the SM and various supersymmetric theories.

hep-ph↗
arXiv2001

General Flavour Blind MSSM and CP Violation

We study FCNC and CP violating processes in the MSSM without a new flavour structure (flavour blind MSSM). The low energy parameters are determined by the running of the soft breaking terms from the GUT scale with SUSY phases consistent with the EDM constraints. We find that the CP asymmetry in b -> s gamma can reach large values potentially measurable at B factories, especially in the low BR(b -> s gamma) region. We analyze the SUSY contributions to the anomalous magnetic moment of the muon pointing out its impact on the b -> s gamma CP asymmetry and on the SUSY spectrum.

hep-ph↗
arXiv2001

Complex flavour couplings in supersymmetry and unexpected CP-violation in the decay B -> phi K

Complex flavour couplings (off-diagonal mass terms) in the squark sector of supersymmetric theories may drastically alter both the rate and the CP-violating asymmetry of certain B-meson decays. We consider the effects of couplings that induce b -> s transitions and lead to final state with strangeness one. We investigate the bounds that must be satisfied by the new terms and explore the possible implications on direct and mixing induced asymmetries in the charged and neutral B -> J/Psi K and B -> phi K decays.

hep-ph↗
arXiv2001

Extended Minimal Flavour Violating MSSM

The recently reported measurements of the CP asymmetry a(psi K) by the BABAR and BELLE collaborations are in good agreement with the standard model prediction. With the anticipated precision in a(psi K) at the B factories and hadron colliders, one hopes to pin down any possible deviation from the SM. We discuss an extension of the MFV-supersymmetric models which comfortably accommodates the current measurements of the CP asymmetry a(psi K), but differs from the SM due to an additional flavour changing structure beyond the CKM matrix. We analyze the compatibility of this model with present data and suggest specific tests in forthcoming experiments in B physics. In addition to the CP-asymmetries in B-meson decays and the Bs-bar(Bs) mass difference, we emphasize measurements of the radiative transition b -> d gamma as sensitive probes of the postulated flavour changing structure. Interestingly, the CKM-unitarity analysis in these models also allows solutions with gamma > pi/2, where gamma=-arg(Vub). Such large values of gamma are hinted by the current measurements of the branchig ratios for the decays B -> pi pi and B -> K pi.

hep-ph↗
arXiv2001

Extended Minimal Flavour Violating MSSM and Implications for B Physics

The recently reported measurements of the CP asymmetry a(psi K) by the BABAR and BELLE collaborations are in good agreement with the standard model (SM) prediction, resulting from the unitarity of the CKM matrix. The so-called minimal flavour violating (MFV) supersymmetric extensions of the standard model, in which the CKM matrix remains the only flavour changing structure, predict a(psi K) similar to the one in the SM. With the anticipated precision in a(psi K) and other CP asymmetries at the B factories and hadron colliders, one hopes to pin down any possible deviation from the SM. We discuss an extension of the MFV-supersymmetric models which comfortably accommodates the current measurements of the CP asymmetry a(psi K), but differs from the SM and the MFV-supersymmetric models due to an additional flavour changing structure beyond the CKM matrix. We suggest specific tests in forthcoming experiments in B physics. In addition to the CP-asymmetries in B-meson decays, such as a(psi K) and a(pi pi), and the mass difference Delta M_s in the Bs-bar(Bs) system, we emphasize measurements of the radiative transition b -> d gamma as sensitive probes of the postulated flavour changing structure. Interestingly, the CKM-unitarity analysis in the Extended-MFV model also allows solutions rho < 0, as opposed to the SM and the MFV models for which only rho > 0 solutions are now admissible, implying gamma > pi/2, where gamma=- arg (Vub). Such large values of gamma are hinted by the current measurements of the branching ratios for the decays B -> pi pi and B -> K pi.

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