Paolo Gambino - Torino

Paolo Gambino
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Paolo Gambino

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High Energy Physics - Phenomenology (39)
High Energy Physics - Experiment (14)
High Energy Physics - Theory (1)

Publications Authored By Paolo Gambino

We use recent Belle results on $\bar{B}^0\rightarrow D^{*+}l^-\bar{\nu}_l$ decays to extract the CKM element $|V_{cb}|$ with two different but well-founded parameterizations of the form factors. We show that the CLN and BGL parameterizations lead to quite different results for $|V_{cb}|$ and provide a simple explanation of this unexpected behaviour. A long lasting discrepancy between the inclusive and exclusive determinations of $|V_{cb}|$ may have to be thoroughly reconsidered. Read More

We re-examine the determination of $|V_{cb}|$ from $B\to D \ell \nu$ in view of recent experimental and theoretical progress, discussing the parameterization of the form factors and studying the role played by the unitarity constraints. Our fit to experimental and lattice results for $B\to D \ell \nu$ gives $|V_{cb}|=40.49(97)\ 10^{-3}$ and to $R(D)= 0. Read More

We study the effect of dimension 7 and 8 operators on inclusive semileptonic B decays and the extraction of |Vcb|. Using moments of semileptonic B decay spectra and information based on the Lowest-Lying State saturation Approximation (LLSA) we perform a global fit of the nonperturbative parameters of the heavy quark expansion including for the first time the O(1/mb^{4,5}) contributions. Higher power corrections appear to have a very small effect on the extraction of |Vcb|, independently of the weight we attribute to the LLSA. Read More

We use artificial neural networks to parameterize the shape functions in inclusive semileptonic $B$ decays without charm. Our approach avoids the adoption of functional form models and allows for a straightforward implementation of all experimental and theoretical constraints on the shape functions. The results are used to extract $|V_{ub}|$ in the GGOU framework and compared with the original GGOU paper and the latest HFAG results, finding good agreement in both cases. Read More

The magnitude of the CKM matrix elements Vcb can be extracted from inclusive semileptonic B decays in a model independent way pioneered by Kolya Uraltsev and collaborators. I review here the present status and latest developments in this field. Read More

The $m_{\scriptscriptstyle W}-m_{\scriptscriptstyle Z}$ interdependence in the Standard Model is studied at $O(\alpha^2) $ in the $\overline{MS}$ scheme. The relevant radiative parameters, $\Delta \hat{\alpha} (\mu),\, \Delta \hat{r}_{W},\, \hat{\rho}$ are computed at the full two-loop level augmented by higher-order QCD contributions and by resummation of reducible contributions. We obtain $m_{\scriptscriptstyle W} = 80. Read More

We extract the magnitude of the CKM matrix element Vcb and the most relevant parameters of the Heavy Quark Expansion from data of inclusive semileptonic B decays. Our calculation includes the recently computed O(alphas Lambda^2/mb^2) corrections and a careful estimate of the residual theoretical uncertainty. Using a recent determination of the charm quark mass, we obtain |Vcb| = (42. Read More

We compute the $O(\alpha_s)$ corrections to the Wilson coefficient of the chromomagnetic operator in inclusive semileptonic B decays. The results are employed to evaluate the complete $O(\alpha_s \Lambda^2/m_b^2)$ correction to the semileptonic width and to the first moments of the lepton energy distribution. Read More

We perform global fits to the moments of semileptonic B decay distributions and extract |V_cb|, the heavy quark masses, and the non-perturbative parameters of the heavy quark expansion. We include NNLO perturbative corrections and recent determinations of the charm mass, and discuss how they improve the precision of the global fit. In particular, using the m_c determination of Ref. Read More

We compute the O(alpha_s) corrections to the Wilson coefficient of the kinetic operator in inclusive semileptonic B decays. Our analytic calculation agrees with reparameterization invariance and with previous numerical results and paves the way to the calculation of analogous corrections to other power-suppressed coefficients. Read More

We present a QCD analysis of heavy quark mesons focussing on the B -> D* formfactor at zero recoil, F_D*(1). An advanced treatment of the perturbative corrections in the Wilsonian approach is presented. We estimate the higher-order power corrections to the OPE sum rule and describe a refined analysis of the nonresonant continuum contribution. Read More

The calculation of the moments in inclusive B meson semileptonic decays is upgraded to O(alphas^2). The first three moments of the lepton energy and invariant hadronic mass distributions are computed for arbitrary cuts on the lepton energy and in various renormalization schemes, finding in general small deviations from the O(alphas^2 beta0) calculation. I also review the relation between MSbar and kinetic heavy quark masses. Read More

We review recent experimental and theoretical developments in inclusive semileptonic B -> Xc l nu decays. In particular, we discuss the determination of |Vcb| and of the heavy quark masses through fits based on the Operator Product Expansion. Read More

We examine the B -> D* form factor at zero recoil using a continuum QCD approach rooted in the heavy quark sum rules framework. A refined evaluation of the radiative corrections as well as the most recent estimates of higher order power terms together with more careful continuum calculation are included. An upper bound on the form factor of F(1)< 0. Read More

We search for signals of Weak Annihilation in inclusive semileptonic D decays. We consider both the widths and the lepton energy moments, which are quite sensitive probes. Our analysis of Cleo data shows no clear evidence of Weak Annihilation, and allows us to put bounds on their relevance in charmless B semileptonic decays. Read More

We compute the O(alpha_s) corrections to the Wilson coefficients of the dimension five operators emerging from the Operator Product Expansion of inclusive radiative B decays. We discuss the impact of the resulting O(alpha_s Lambda_QCD^2/m_b^2) corrections on the extraction of m_b and mu_pi^2 from the moments of the photon spectrum. Read More

The inclusive semileptonic branching ratio is often employed to normalize other inclusive B decays. Using recent determinations of the non-perturbative parameters of the Operator Product Expansion we compute the normalization factor for the branching ratio of B->X_s gamma and find a few percent enhancement with respect to previous determinations. Read More

We compute the fully-differential B -> X_u l nu decay width to all orders in perturbation theory in the large-beta0 limit. Each of the five structure functions that build the hadronic tensor is expressed as a Borel integral, summing up O(CF beta0^{n-1} alpha_s^n) corrections for any n. We derive analytic expressions for the Borel transforms of both real and virtual diagrams with a single dressed gluon, and perform an all-order infrared subtraction, where the Borel parameter serves also as an infrared regulator. Read More

I briefly review the theoretical status of semileptonic and radiative B decays in 2005. Read More

We report OPE predictions for hadronic mass and q^2 moments in inclusive semileptonic B decays without charm, taking into account experimental cuts on the charged lepton energy and on the hadronic invariant mass, and address the related theoretical uncertainty. Read More

The latest Belle and BaBar measurements of the inclusive B -> X_s l^+ l^- branching ratio have smaller errors and lower central values than the previous ones. We point out that these results indicate that the sign of the b -> s gamma amplitude is the same as in the SM. This underscores the importance of B -> X_s l^+ l^- in searches for new physics, and may be relevant for neutralino dark matter analyses within the MSSM. Read More

We report the OPE-based predictions for a number of lepton energy and hadronic mass moments in the inclusive semileptonic B -> X_c \ell\nu decays with a lower cut on the charged lepton energy. We rely on the direct OPE approach where no expansion in the charm mass is employed and the theoretical input is a limited set of underlying OPE parameters including m_b and m_c. A Wilsonian treatment with a `hard' cutoff is applied using running low-scale masses m_Q(\mu) and kinetic expectation value \mu_\pi^2(\mu). Read More

We complete the next-to-next-to-leading order QCD calculation of the branching ratio for B -> X_s l^+ l^- including recent results for the three-loop anomalous dimension matrix and two-loop matrix elements. These new contributions modify the branching ratio in the low-q^2 region, BR_ll, by about +1% and -4%, respectively. We furthermore discuss the appropriate normalization of the electromagnetic coupling alpha and calculate the dominant higher order electroweak effects, showing that, due to accidental cancellations, they change BR_ll by only -1. Read More

Overall, the Standard Model describes electroweak precision data rather well. There are however a few areas of tension (charged current universality, NuTeV, (g-2)_\mu, b quark asymmetries), which I review emphasizing recent theoretical and experimental progress. I also discuss what precision data tell us about the Higgs boson and new physics scenarios. Read More

We compute the complete O(alphas^2) anomalous dimension matrix relevant for the b to s gamma, b to s gluon and b to s l+l- transitions in the standard model and some of its extensions. For radiative decays we confirm the results of Misiak and Munz, and of Chetyrkin, Misiak and Munz. The O(alphas^2) mixing of four-quark into semileptonic operators is instead a new result and represents one of the last missing ingredients of the next-to-next-to-leading-order analysis of rare semileptonic B meson decays. Read More

Present global fits to electroweak data are characterized by two results that differ from Standard Model expectations by about 3 sigma, the NuTeV measurement of sin^2theta_W and the FB b quark asymmetries measured at LEP. I review possible SM and new physics explanations of these anomalies and the implications for the indirect determination of the Higgs mass. Read More

The ratio between the photon spectrum in B -> X_s gamma and the differential semileptonic rate wrt the hadronic variable M_X/E_X is a short-distance quantity calculable in perturbation theory and independent of the Fermi motion of the b quark in the B meson. We present a NLO analysis of this ratio and show how it can be used to determine |V_ub/V_cb| independently of any model for the shape function. We also discuss how this relation can be used to test the validity of the shape-function theory on the data. Read More

We compute the complete two-loop O(alpha) Wilson coefficients relevant for radiative decays of the B meson in the SM. This is a necessary step in the calculation of the O(alpha alpha_s^n ln^n m_b/M_W) corrections and improves on our previous analysis of electroweak effects in B -> X_s gamma. We describe in detail several interesting technical aspects of the calculation and include all dominant QED matrix elements. Read More

The charm-loop contribution to B -> Xs gamma is found to be numerically dominant and very stable under logarithmic QCD corrections. The strong enhancement of the branching ratio by QCD logarithms is mainly due to the b-quark mass evolution in the top-quark sector. These observations allow us to achieve better control over residual scale dependence at the next-to-leading order. Read More

Affiliations: 1CERN, 2Yonsei, 3Cambridge, 4Bristol, 5Oxford, 6Manchester, 7Aachen, 8Bristol, 9Royal Holloway, 10CERN, 11CERN, 12Cambridge, 13KEK, 14Sussex, 15Edinburgh, 16Oxford, 17Royal Holloway, 18Manchester, 19Zurich

We review theoretical and experimental results on CP violation summarizing the discussions in the working group on CP violation at the UK phenomenology workshop 2000 in Durham. Read More

We compute the two-loop electroweak corrections to the radiative decays of the B meson in the SM. Electroweak effects reduce the Wilson coefficient C_7^eff(mw) by 2.6% for a light Higgs boson of about 100 GeV and are less important for a heavier Higgs. Read More

In a generic gauge theory the gauge parameter dependence of individual Green functions is controlled by the Nielsen identities, which originate from an enlarged BRST symmetry. We give a practical introduction to the Nielsen identities of the Standard Model (SM) and to their renormalization and illustrate the power of this elegant formalism in the case of the problem of the definition of mass.We prove to all orders in perturbation theory the gauge-independence of the complex pole of the propagator for all physical fields of the SM, in the most general case with mixing and CP violation. Read More

Recent calculations of the two-loop electroweak effects enhanced by powers of the top mass have been implemented in the main electroweak libraries and have an important effect on the indirect determination of the Higgs mass MH. I briefly review the main results of these calculations and discuss in detail the residual uncertainties and their impact on the global fit to MH. The perspectives for the near future are also considered. Read More

The electroweak corrections induced by a heavy top on the main precision observables are now available up to O(g^4 mt^2/mw^2). The new results significantly reduce the theoretical uncertainty and have a sizable impact on the determination of sin^2theta_eff. We give precise predictions for mw and the effective sine in different renormalization schemes, estimate their accuracy, and discuss the implications for the indirect determination of M_H. Read More

The radiative corrections involved in the precise determination of the electroweak mixing angle measured at the Z-peak are reviewed in detail, with particular emphasis on the new calculation of two-loop heavy top effects. This example serves as a brief pedagogical introduction to the problems and techniques of higher order electroweak calculations. Read More

The corrections induced by a heavy top on the main precision observables are now available up to O(alpha^2 mt^2/mw^2). The new results imply a significant reduction of the theoretical uncertainty and can have a sizable impact on the determination of the effective sine. Read More

At a linear collider of the next generation the large event rates expected from Bhabha and M\o ller scattering may be used to determine simultaneously sin^2\theta_w and the polarization of both beams with very high accuracy. These measurements can be performed in parallel to the other tasks of the linear collider as a free by-product. A high degree of polarization and a good polar angle coverage of the detectors turn out to be major assets. Read More

Affiliations: 1New York University, 2New York University

Leading QCD vacuum polarization contributions to the electroweak parameter $\delta\rho$ are evaluated numerically using several different prescriptions for the gluon self-energy. Simple theoretical estimates of the asymptotic behavior are given. The results show a significant contribution from the leading infrared renormalons when $\delta\rho$ is expressed in terms of the top-quark pole mass and its absence when the $\msbar$ running mass is employed. Read More

Recent developments in the field of high precision calculations in the Standard Model are illustrated with particular emphasis on the evidence for radiative corrections and on the estimate of the theoretical error in perturbative calculations. Read More