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F. S. Navarra

Publications and source records attributed to F. S. Navarra.

At least 199 records · Page 11Linked to original sources
arXiv1999

Meson Cloud and SU(3) Symmetry Breaking in Parton Distributions

We apply the Meson Cloud Model to the calculation of nonsinglet parton distributions in the nucleon sea, including the octet and the decuplet cloud baryon contributions. We give special attention to the differences between nonstrange and strange sea quarks, trying to identify possible sources of SU(3) flavor breaking. A analysis in terms of the $κ$ parameter is presented, and we find that the existing SU(3) flavor asymmetry in the nucleon sea can be quantitatively explained by the meson cloud. We also consider the $Σ^+$ baryon, finding similar conclusions.

hep-ph↗
arXiv1999

Hyperon-nucleon coupling from QCD sum rules

The NKY coupling constant for $Y = Λ$ and $Σ$ is evaluated in a QCD sum rule calculation. We discuss and extend the result of a previous analysis in the $\rlap{/}{q}iγ_5$ structure and compare it with the result obtained with the use of the $γ_5 σ_{μν}$ structure. We find a huge violation of the SU(3) symmetry in the $γ_5 σ_{μν}$ structure.

hep-ph↗
arXiv1999

Charmonium-Hadron Cross Section in a Nonperturbative QCD Approach

We calculate the nonperturbative $J/Ψ-N$ and $Ψ'-N$ cross sections with the model of the stochastic vacuum which has been succesfully applied in many high energy reactions. We also give a quantitative discussion of pre-resonance formation and medium effects.

hep-ph↗
arXiv1999

Testing the Meson Cloud Model in Inclusive Meson Production

We have applied the Meson Cloud Model to calculate inclusive momentum spectra of pions and kaons produced in high energy proton-proton and proton-nucleus collisions. For the first time these data are used to constrain the cloud cut-off parameters. We show that it is possible to obtain a reasonable description of data, especially the large $x_F$ ($x_F \geq 0.2$) part of the spectrum and at the same time describe (partially) the E866 data on $\bar d - \bar u$ and $\bar d / \bar u$. We also discuss the relative strength of the $πN$ and $πΔ$ vertices. We find out that the corresponding cut-off parameters should be both soft and should not differ by more than 200 MeV from each other. An additional source (other than the meson cloud) of sea antiquark asymmetry, seems to be necessary to completely explain the data. A first extension of the MCM to proton nucleus collisions is discussed.

hep-ph↗
arXiv1999

Form Factors and Decay Rates for Heavy $Λ$ Semileptonic Decays from QCD Sum Rules

QCD sum rules for the determination of form factors of $Λ_b$ and $Λ_c$ semileptonic decays are investigated. With a form for the baryonic current appropriate for the limits of the heavy quark symmetries, the different tensor structures occurring in the two- and three-point functions are separately studied, and in each case general relations are written for the form factors. Particular attention is given to the treatment of the kinematical region ascribed to the continuum. The $t$-dependence of the form factors and the decay rates are numerically evaluated and compared to experimental information.

hep-ph↗
arXiv1999

$g_{NKΛ}$ and $g_{NKΣ}$ from QCD Sum Rules in the $γ_5 σ_{μν}$ structure

The NKY coupling constant for $Y = Λ$ and $Σ$ is evaluated in a QCD sum rule calculation. We study the Borel sum rule for the three point function of one pseudoscalar one nucleon and one hyperon current up to order six in the operator product expansion. The Borel transform is performed with respect to the nucleon and hyperon momenta, which are taken to be equal. We discuss and extend the result of a previous analysis in the $\rlap{/}{q}iγ_5$ structure and compare it with the result obtained with the use of the $γ_5 σ_{μν}$ structure. We find that the effect of pole-continuum transitions is very important in the $\rlap{/}{q}iγ_5$ structure and that it changes completely results obtained in previous analysis.

nucl-th↗
arXiv1998

Systematics of Leading Particle Production

Using a QCD inspired model developed by our group for particle production, the Interacting Gluon Model (IGM), we have made a systematic analysis of all available data on leading particle spectra. These data include diffractive collisions and photoproduction at HERA. With a small number of parameters (essentially only the non-perturbative gluon-gluon cross section and the fraction of diffractive events) good agreement with data is found. We show that the difference between pion and proton leading spectra is due to their different gluon distributions. We predict a universality in the diffractive leading particle spectra in the large momentum region, which turns out to be independent of the incident energy and of the projectile type.

hep-ph↗
arXiv1998

Alternative Linear Chiral Models for Nuclear Matter

The equation of state of a family of alternative linear chiral models in the mean field approximation is discussed. We investigate the analogy between some of these models with current models in the literature, and we show that it is possible to reproduce very well the saturation properties of nuclear matter.

nucl-th↗
arXiv1998

$g_{NDΛ_{c}}$ from QCD Sum Rules

The $NDΛ_c$ coupling constant is evaluated in a full QCD sum rule calculation. We study the Borel sum rule for the three point function of one pseudoscalar one nucleon and one $Λ_c$ current up to order seven in the operator product expansion. The Borel transform is performed with respect to the nucleon and $Λ_c$ momenta, which are taken to be equal, whereas the momentum $q^2$ of the pseudoscalar vertex is taken to be zero. This coupling constant is relevant in the meson cloud description of the nucleon which has been recently used to explain exotic events observed by the H1 and ZEUS Collaborations at HERA.

hep-ph↗
arXiv1998

Leading Particle Effect in the $J/Ψ$ Elasticity Distribution

Recent DESY-HERA data on $J/Ψ$ elasticity distribution show that it emerges mostly as a fast particle. Interpreting photoproduction as a collision between a pre-formed charmed hadron and the proton, the outcoming $J/Ψ$ is a leading particle of the collision. We analyse these data using a model formulated to describe energy flow in hadron-hadron reactions. The measured $J/Ψ$ spectrum can be successfully described in terms of this model. We conclude that the observed transparency of the charmed hadron-proton collisions arises because of the particularly small gluonic content of the initial $c - \bar c$ state.

hep-ph↗
arXiv1998

K^* Mesons and Nucleon Strangeness

We study contributions to the nucleon strange quark vector current form factors from intermediate states containing K^* mesons. We show how these contributions may be comparable in magnitude to those made by K mesons, using methods complementary to those employed in quark model studies. We also analyze the degree of theoretical uncertainty associated with K^* contributions.

hep-ph↗
arXiv1997

Diffractive Mass Spectra at DESY-HERA in the Interacting Gluon Model

We have applied the Interacting Gluon Model (IGM) to calculate diffractive mass spectra measured recently in e-p collisions at HERA. We show that it is possible to treat them in terms of gluon-gluon collisions in the same way as was done before for hadronic collisions. Analysis of available data is performed.

hep-ph↗
arXiv1997

Looking for Exotic Multiquark States in Nonleptonic B Decays

Recent data on inclusive B decays into charmonium states taken by the CLEO collaboration suggest that a sizeable fraction of the nonleptonic decays may consist of the $J/ψΛ\overline p$ three body final state, corresponding to a distinct enhancement in the inclusive $J/ψ$ momentum distribution. The kinematical boundary of this structure corresponds to the case where the $J/ψ$ recoils nearly monoenergetically in the B rest system against a partner having mass of $\simeq$ 2 GeV. This may allow the observation of a $Λ-\overline p $ bound state near or just below threshold; i.e., strange baryonium, even if the production rate is small. Using a phase space approach to the B meson decay, we study the $J/ψ$ momentum distribution and the effect of baryonium formation. We also discuss the possible observation of pentaquarks and hadronically-bound $J/ψ$ by the observation of monoenergetic baryons in these decays.

hep-ph↗
arXiv1996

Diffractive Dissociation In The Interacting Gluon Model

We have extended the Interacting Gluon Model (IGM) to calculate diffractive mass spectra generated in hadronic collisions. We show that it is possible to treat both diffractive and non-diffractive events on the same footing, in terms of gluon-gluon collisions. A systematic analysis of available data is performed. The energy dependence of diffractive mass spectra is addressed. They show a moderate narrowing at increasing energies. Predictions for LHC energies are presented.

hep-ph↗
arXiv1996

Virtual Meson Cloud of the Nucleon and Intrinsic Strangeness and Charm

We have applied the Meson Cloud Model (MCM) to calculate the charm and strange antiquark distribution in the nucleon. The resulting distribution, in the case of charm, is very similar to the intrinsic charm momentum distribution in the nucleon. This seems to corroborate the hypothesis that the intrinsic charm is in the cloud and, at the same time, explains why other calculations with the MCM involving strange quark distributions fail in reproducing the low x region data. From the intrinsic strange distribution in the nucleon we have extracted the strangeness radius of the nucleon, which is in agreement with other meson cloud calculations.

hep-ph↗
arXiv1995

Leading Charm Production in the Interacting Gluon Model

We discuss leading charm production in connection with energy deposition in the central rapidity region. Special attention is given to the correlation between production in central and fragmentation regions. If the fraction of the reaction energy released in the central region increases the asymmetry in the $x_F$ distributions of charmed mesons will become smaller. We illustrate this quantitatively with simple calculations performed using the Interacting Gluon Model. Leading beauty production is also considered.

hep-ph↗
arXiv1995

Temperature dependence of heavy meson masses

Using a previously derived QCD effective hamiltonian we find the masses of heavy quarkonia states. Non perturbative effects are included through temperature dependent gluonic condensates. We find that even a moderate change in these condensates in a hot hadronic environment (below the deconfining transition) is sufficient to significantly change the heavy meson masses.

hep-ph↗