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G. Nardulli

Publications and source records attributed to G. Nardulli.

At least 91 records · Page 5Linked to original sources
arXiv1995

JET ANALYSIS BY NEURAL NETWORKS IN HIGH ENERGY HADRON-HADRON COLLISIONS

We study the possibility to employ neural networks to simulate jet clustering procedures in high energy hadron-hadron collisions. We concentrate our analysis on the Fermilab Tevatron energy and on the $k_\bot$ algorithm. We consider both supervised multilayer feed-forward network trained by the backpropagation algorithm and unsupervised learning, where the neural network autonomously organizes the events in clusters.

hep-ph↗
arXiv1994

Chiral Effective Theory for Heavy Mesons

I review recent developments in the description of the interactions between light and heavy mesons by an effective chiral lagrangian having the symmetries of the Heavy Quark Effective Theory. In particular the problem of the determination of the strong coupling constants $g_{P^* P π}$ and $g_{P^* P ρ}$ ($P, P^*=$ heavy mesons) is addressed. Invited talk given at the 18th J. Hopkins Workshop (Florence, September 1994)

hep-ph↗
arXiv1994

Heavy Meson Hyperfine Splitting: A Complete $1/m_Q$ Calculation

The hyperfine splittings $Δ_D=(m_{D^*_s}-m_{D_s})-(m_{D^{*+}}-m_{D^+})$ and $Δ_B=(m_{B^*_s}-m_{B_s})-(m_{B^{*0}}-m_{B^0})$ are analyzed in the framework of an effective lagrangian possessing chiral, heavy flavour and spin symmetries, explicitly broken by a complete set of first order terms. Among these terms, those responsible for the difference between the couplings $\gis$ and $\gi$ are evaluated in the QCD sum rules approach. Their contribution to $Δ_D$ and to $Δ_B$ appears to quantitatively balance previously estimated chiral effects nice agreement with the experimental data, solving a suspected puzzle for heavy quark theory.

hep-ph↗
arXiv1994

$D^*$ Radiative Decays and Strong Coupling of Heavy Mesons with Soft Pions in a QCD Relativistic Potential Model

In the framework of a QCD inspired relativistic potential model, we evaluate radiative decay rates of heavy mesons and their coupling with soft pions. The agreement with the existing experimental data is satisfactory. In the limit $m_Q \to \infty$ one obtains results in agreement with the Heavy Quark Effective Theory and is able to predict the values of the relevant couplings; in particular, for the scaled $B^*B π$ strong coupling constant $g$, we find that the non relativistic constituent quark model prediction $g=1$ is modified, by the inclusion of the relativistic effects due to the light quarks, to the value $g=1/3$, in agreement with recent QCD sum rules determination.

hep-ph↗
arXiv1994

On the coupling of heavy mesons to pions in QCD

We compute the strong coupling constant $g_{P^* P π}$, with $P$ and $P^*$ respectively pseudoscalar and vector heavy mesons by using the QCD sum rules approach. Our computation is based on the evaluation of the time ordered product of currents between the vacuum and the soft pion state. The so-called parasitic terms are taken into account and give a contribution to the sum rule of the same order of the lowest lying state, while higher dimension non perturbative terms have small numerical effects. The infinite heavy quark mass limit is also examined.

hep-ph↗
arXiv1994

Higgs Search by Neural Networks at LHC

We show that neural network classifiers can be used to discriminate Higgs production from background at LHC for $ 150< M_H<200$ GeV. The results compare favourably with ordinary multivariate analysis.

hep-ph↗
arXiv1993

Theoretical Approaches to $B \to K^* γ$

We describe two recent theoretical calculations of the $B \to K^* γ$ decay. The first method is based on an effective lagrangian incorporating chiral symmetry for the light degrees of freedom and the heavy quark spin-flavor symmetries for the heavy quarks. Using these symmetries, together with the hypothesis of polar q$^2$ dependence of the semileptonic form factors, one is able to relate $B \to K^* γ$ and $D \to K^* \ell ν$ decays with the result $ R \, =\, Γ(B \to K^* γ) / Γ(b \to s γ) = 0.09 \pm 0.03$. The second method is based on 3-point function QCD sum rules and gives the result $ R \, = \, 0.17 \pm 0.05$. Both results are in reasonable agreement with recent data from the CLEO II Collaboration.

hep-ph↗
arXiv1993

Radiative $B \to K^* γ$ transition in QCD

We evaluate the branching ratios of the radiative decays $B \to K^* γ$, and $B \to K_1 γ$ in the framework of three-point function QCD sum rules. We find: $ Γ(B \to K^* γ) / Γ(b \to s γ) = 0.17 \pm 0.05$ and $ Γ(B \to K_1 γ) / Γ(b \to s γ) = 0.30 \pm 0.15$. We also study, in the infinite quark mass limit, the connection between the form factor of the radiative $B \to K^* γ$ transition and the weak hadronic form factors entering the semileptonic B-meson decays.

hep-ph↗
arXiv1993

Two Body Non Leptonic Decays of B and B_s Mesons

We perform an analysis of two-body non leptonic decays of $B$ and $B_s$ mesons in the factorization approximation. We make use of the semileptonic decay amplitudes previously calculated on the basis of an effective lagrangian satisfying chiral and heavy quark symmetries and including spin 1 resonances. Exclusive semileptonic $D$-decay data are used as experimental input. Our results compare favorably with data, whenever they are available and indicate a positive value for the ratio of non leptonic coefficients $a_2/a_1$, similarly to previous studies.

hep-ph↗
arXiv1993

Radiative Heavy Meson Transitions

We evaluate the radiative and hadronic decay rates of the $D^*$ mesons using the Heavy Quark Effective Theory and the Vector Meson Dominance hypothesis. We also estimate the width of the $B^*$ electromagnetic transitions and the radiative decays of positive parity $J^P=0^+, 1^+$ charmed mesons.

hep-ph↗
arXiv1993

Effective Lagrangian for Heavy and Light Mesons: Radiative B Decays

We make use of the information obtained from semileptonic decays of $B$ and $D$ mesons, within an effective lagrangian description based on heavy quark theory and on chiral expansion, to study the radiative decays $B \to K^\star γ$ and $B_S \to ϕγ$, and the pair conversion processes $B \to K e^+e^-$ and $B \to K^\star e^+e^-$. We discuss with care the required extrapolations from zero recoils. We obtain a BR($B\to K^\starγ$) between $1.3\times 10^{-5}$ and $4.1\times 10^{-5}$ and BR($B_s \toϕγ$) between $1.4\times 10^{-5}$ and $4.5\times 10^{-5}$, with errors mainly arising from the present uncertainty in the Kobayashi-Maskawa element $|V_{ts}|$. For the pair conversion processes we study in particular the lepton effective mass distributions whose measurements would allow for an understanding both long distance and short distance contributions to such processes.

hep-ph↗
arXiv1993

Hadronic Transitions among Quarkonium States in a Soft-Exchange-Approximation. Chiral Breaking and Spin Symmetry Breaking Processes

Although no asymptotic heavy quark spin symmetry, and even more no flavor symmetry, are expected for systems such as quarkonium, a numerical discussion shows that for some processes and in a preasymptotic region which may roughly include charmonium and bottomonium, the use of the spin-symmetry may be useful in conjunction with chiral symmetry for light hadrons (soft-exchange- approximation regime, SEA). We continue our discussion of hadronic transitions in the SEA-regime by studying in particular chiral breaking transitions such as $~^3P' \to ~^3Pπ^0$, $~^3Pη$, level splittings and transitions which break both chiral and spin symmetry, such as $ψ' \to J/ψπ^0$, $J/ψη$, and $~^1P_1 \to J/ψπ^0$.

hep-ph↗
arXiv1993

QCD Sum Rules and B Decays

We review some recent applications of QCD sum rules to $B$-decays. These include the determination of the leptonic constant $f_B$ and of the semileptonic transition amplitudes of the $B$-meson into negative and positive parity charmed states.

hep-ph↗
arXiv1993

Theory Review of CP Violations in B Decays at Hadron Colliders

CP violations in B meson decays at hadron colliders are reviewed. In particular I examine: $B^0-\bar{B^0}$ mixing and oscillations within Standard Model and the Cabibbo-Kobayashi-Maskawa picture for CP violations; $B^0$ decays into CP eigenstates and the measurements of the angles in the unitarity triangle; finally I consider a class of charged $B$ decays that allow to avoid uncertainties arising from the computation of hadronic matrix elements.

hep-ph↗
arXiv1993

$B_c$ Physics at Hadron Colliders

In this paper we summarize the results of the theory working group dedicated to the analysis of $B_c$ production at hadron colliders.

hep-ph↗
arXiv1993

Study of the Reactions $B \to D^* ππ$ and $B \to D^* ρπ$

We evaluate the non leptonic decays $B \to D^* ππ$ and $B \to D^* ρπ$ in the limit of infinitely heavy quarks, assuming the dominance of intermediate positive parity charmed resonances. We find that the branching ratios are of the order $10^(-3)$.

hep-ph↗
arXiv1992

Effective Lagrangian for Heavy and Light Mesons: Semileptonic Decays

We introduce an effective lagrangian including negative and positive parity heavy mesons containing a heavy quark, light pseudoscalars, and light vector resonances, with their allowed interactions, using heavy quark spin-flavour symmetry, chiral symmetry, and the hidden symmetry approach for light vector resonances. On the basis of such a lagrangian, by considering the allowed weak currents and by including the contributions from the nearest unitarity poles we calculate the form factors for semileptonic decays of $B$ and $D$ mesons into light pseudoscalars and light vector resonances. The available data, together with some additional assumptions, allow for a set of predictions in the different semileptonic channels, which can be compared with those following {}from different approaches. A discussion of non-dominant terms in our approach, which attempts at including a rather complete dynamics, will however have to wait till more abundant data become available.

hep-ph↗