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. Many years ago, it has been suggested by Sullivan [1] that some fraction of the nucleon's anti-quark sea distribution may be associated with non-perturbative processes like the pion * 1 cloud of the nucleon. The generalization of this process to other mesons is depicted in figs. 1a and b, and was used in refs. [2,3] to calculate the strange and anti-strange sea quark distributions in the nucleon.Recent analysis of deep inelastic neutrino-hadron scattering data [4] renewed the interest on the meson cloud picture of the nucleon. It is well known that, in this picture there is an asymmetry between sea quark and anti-quark momentum distributions [2]. This happens because the quark and the anti-quark are in different hadronic bound states. On the other hand, in extracting sea distributions from hard processes, it is usually assumed that the quark and antiquark sea contributions are equal. From the point of view of QCD, no definite statement on this subject can be made. Based on charge conjugation symmetry it is only possible to say that the quark sea distribution in the nucleon is equal to the antiquark sea distribution in the antinucleon. In ref. [4] it is shown that, in contrast to the meson cloud approach expectation, the sea strange and anti-strange quark distributions are quite similar. At first sight this would be a very strong argument against the relevance of the meson cloud [5]. The attempt to explain experimental data with the meson cloud model performed in refs. [2,3] has shown not only that the asymmetry present in this model seems to be in conflict with data but also that the calculated distributions are far below data for x < 0.3. However, in ref.[6], these data were reconsidered and combined with the CTEQ collaboration analysis [7]. The conclusion of the authors was that, considering the error bars, existing data do not exclude some asymmetry between the strange and anti-strange momentum distributions, which is significant only for x > 0.2 − 0.3.In the present work we apply the meson cloud model (MCM) to study strangeness and charm in the nucleon. In the case of strangeness, we shall try to extract some estimates on the strangeness radius of the nucleon. This is a very interesting quantity from both theoretical and phenomenological point of view. Indeed, approved parity-violating lepton scattering experiments at MIT-Bates [8] and CEBAF [9] will provide information on ...

We have extended the interacting gluon model to calculate diffractive mass spectra generated in hadronic collisions. We show that it is possible to treat both diffractive and nondiffractive 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 CERN LHC energies are presented. ͓S0556-2821͑97͒06703-9͔

Improving previous calculations, we compute the D +D → J /ψ + π cross section using the most complete effective Lagrangians available. The new crucial ingredients are the form factors on the charm meson vertices, which are determined from QCD sum rules calculations. Some of them became available only very recently, and the last one, needed for our present purpose, is calculated in this work.

At very high energies we expect that the hadronic cross sections satisfy the Froissart bound, which is a well-established property of the strong interactions. In this energy regime we also expect the formation of the Color Glass Condensate, characterized by gluon saturation and a typical momentum scale: the saturation scale Qs. In this paper we show that if a saturation window exists between the nonperturbative and perturbative regimes of Quantum Chromodynamics (QCD), the total cross sections satisfy the Froissart bound. Furthermore, we show that our approach allows us to describe the high energy experimental data on pp/pp total cross sections.

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.

We present an extension of the interacting gluon model, used previously to calculate inelasticities and leading particle spectra in hadronic and nuclear collisions, which incorporate also the production of minijets. As a result we get inelasticity slowly increasing towards some limited value. PACS number(s1: 13.85.Hd, 12.38.Mh, 13.87.CeThe concept of inelasticity plays an important role in cosmic ray and accelerator physics. Whereas in the former it is crucial for the understanding and interpretation of the development of cosmic ray cascades, in the latter it is an indispensable ingredient of any statistical model of multiparticle production processes. Inelasticity is usually defined as the fraction K of the available energy 6 , in a given interaction, effectively employed for multiparticle production. The energy dependence of inelasticity is a problem of great interest both for the interpretation of cosmic ray data and also for quark-gluon plasma (QGP) physics since inelasticity decreasing with energy would make the formation of Q G P more difficult. Experimentally the situation is not clear and many authors have proposed different behavior of the average inelasticity ( K ) as a function of d s [I].One of the models which in a natural way leads to ( K ) decreasing with energy is the interacting gluon model (IGM) 121. It included originally only soft gluonic interactions and used the phenomenological soft gluongluon cross section as an input. However, it was claimed recently that semi-hard QCD interactions (which produce the so-called minijets) represent an important fraction (-25%) of the total cross section already at the CERN collider energies and are expected to be even more important at higher energies [3]. In this paper we discuss therefore the effect of the inclusion of such semihard component to the original IGM.In the framework of the IGM, in a first approximation, valence quarks do not interact at all but instead form leading particles. The interaction is supposed to come entirely from the gluonic contents of the colliding hadrons via the formation of gluonic fireballs (clusters). The originally predicted decrease of ( K ) with energy can be traced to the assumption that the phenomenological behavior of gluon-gluon cross section ugg(9) is limited to 1 /3 < ugg < const behavior, to the 1 /x form of the gluonic structure functions for small x (see below for details) and to the assumed constancy with energy of the percentage p of the energy-momentum of the projectile allocated t o gluons. Here we shall relax the first condition by allowing the QCD semi-hard interaction mechanism which leads to u, increasing with energy. The probability of depositing fractions x and y of the energy momenta of the incoming hadrons in the central region of reaction, by means of the gluon-gluon interactions, is given by the formula [2] where which is defined by the mass m a of the lightest possible produced state.The function w ( x , y ) (called "spectral function") con-(2) tains all the dynamical input of the model and is pro...

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The D * Dπ form factor is evaluated at low and moderate Q 2 in a hadronic loop model, for off-shell D mesons. The results contain arbitrary constants, which are fixed so as to match a previous QCD sum rule calculation valid at higher Q 2 . The form factor obtained in this way is used to extract the coupling constant, which is in very good agreement with the experimental value.