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J. Magnin

Publications and source records attributed to J. Magnin.

At least 37 records · Page 2Linked to original sources
arXiv2001

On the intrinsic charm and the recombination mechanisms in charm hadron production

We study $Λ_c^\pm$ production in $pN$ and $π^-N$ interactions. Recent experimental data from the SELEX and E791 Collaborations at FNAL provide important information on the production mechanism of charm hadrons. In particular, the production of the $Λ_c$ baryon provides a good test of the intrinsic charm and the recombination mechanisms, which have been proposed to explain the so called leading particle effects.

hep-ph↗
arXiv2001

Production asymmetry of D mesons in $γp$ collisions

We study the production asymmetry of charm versus anticharm mesons in photon-proton interactions. We consider photon gluon fusion plus higher order corrections in which light quarks through vector meson-proton interactions contribute to the cross section. Non perturbative effects are included in terms of a recombination mechanism which gives rise to a production asymmetry.

hep-ph↗
arXiv2000

Formation of Liesegang patterns: Simulations using a kinetic Ising model

A kinetic Ising model description of Liesegang phenomena is studied using Monte Carlo simulations. The model takes into account thermal fluctuations, contains noise in the chemical reactions, and its control parameters are experimentally accessible. We find that noisy, irregular precipitation takes place in dimension d=2 while, depending on the values of the control parameters, either irregular patterns or precipitation bands satisfying the regular spacing law emerge in d=3.

cond-mat.stat-mech↗
arXiv2000

/\_c+ - /\_c- production asymmetries in two component models

Experiments on charm hadroproduction have shown a substantial difference in the production of charm and anticharm hadrons. In this work we study /\_c+ and /\_c- inclusive production in p-N interactions in the framework of two component models. We show that the recombination two component model gives a qualitatively and quantitatively good description of /\_c production while the intrinsic charm model seems to be ruled out by recent experimental data from the SELEX Collaboration.

hep-ph↗
arXiv2000

Gluon distributions in nucleons and pions at a low resolution scale

In this paper we study the gluon distribution functions in nucleons and pions at a low resolution $Q^2$ scale. This is an important issue since parton densities at low $Q^2$ have always been taken as an external input which is adjusted through DGLAP evolution to fit the experimental data at higher scales. Here, in the framework of a model recently developed, it is shown that the hypothetical cloud of {\it neutral} pions surrounding nucleons and pions appears to be responsible for the characteristic valence-like gluon distributions needed at the inital low scale. As an additional result, we get the remarkable prediction that neutral and charged pions have different intrinsic sea flavor contents.

hep-ph↗
arXiv2000

Low $Q^2$ wave-functions of pions and kaons and their parton distribution functions

We study the low $Q^2$ wave-functions of pions and kaons as an expansion in terms of hadron-like Fock state fluctuations. In this formalism, pion and kaon wave-functions are related one another. Consequently, the knowledge of the pion structure allows the determination of parton distributions in kaons. In addition, we show that the intrinsic (low $Q^2$) sea of pions and kaons are different due to their different valence quark structure. Finally, we analize the feasibility of a method to extract kaon's parton distribution functions within this approach and compare with available experimental data.

hep-ph↗
arXiv2000

Charge Asymmetries in charm photoproduction

Charm quarks are expected to be produced mainly by the photon-gluon fusion mechanism in photon-Nucleon interactions. However, a small part of the total charm cross section originates in similar processes to those appearing in charm hadroproduction through the resolved (hadronic) component of the photon. Although the contribution of the resolved part of the photon is small at fixed target energies, it can help to understand the small but sizeable charge asymmetries measured in charm hadron photoproduction experiments.

hep-ph↗
arXiv1999

The $bar{d} - \bar{u}$ asymmetry of the proton in a Pion Cloud Model approach

We study the $bar{d} - \bar{u}$ asymmetry of the proton in a model approach in which hadronic fluctuations of the nucleon are generated through gluon splitting and recombination mechanisms. Within this framework, it is shown that the \ud asymmetry of the proton is consistently described by including only nucleon fluctuations to $|πN>$ and $|πΔ>$ bound states. Predictions of the model closely agree with the recent experimental data of the E866/NuSea Collaboration.

hep-ph↗
arXiv1999

Formation of Liesegang patterns: A spinodal decomposition scenario

Spinodal decomposition in the presence of a moving particle source is proposed as a mechanism for the formation of Liesegang bands. This mechanism yields a sequence of band positions x_n that obeys the spacing law x_n~Q(1+p)^n. The dependence of the parameters p and Q on the initial concentration of the reagents is determined and we find that the functional form of p is in agreement with the experimentally observed Matalon-Packter law.

cond-mat.stat-mech↗
arXiv1999

Liesegang patterns : Studies on the width law

The so-called "width law" for Liesegang patterns, which states that the positions x_n and widths w_n of bands verify the relation x_n \sim w_n^α for some α>0, is investigated both experimentally and theoretically. We provide experimental data exhibiting good evidence for values of αclose to 1. The value α=1 is supported by theoretical arguments based on a generic model of reaction-diffusion.

cond-mat.soft↗
arXiv1998

Strange / anti-strange asymmetry in the nucleon sea

We analyze the non-perturbative structure of the strange sea of the nucleon within a meson cloud picture. In a low $Q^2$ approach in which the nucleon is viewed as a three valon bound state, we evaluate the probability distribution of an in-nucleon Kaon-Hyperon pair in terms of splitting functions and recombination. The resulting kaon and hyperon probability densities are convoluted with suitable strange distributions inside the meson and baryon in order to obtain non-perturbative contributions to the strange sea of the nucleon. We find a structured strange/anti-strange asymmetry, displaying a clear excess of quarks (anti-quarks) for large (small) momentum fractions

hep-ph↗
arXiv1998

Liesegang patterns: Effect of dissociation of the invading electrolyte

The effect of dissociation of the invading electrolyte on the formation of Liesegang bands is investigated. We find, using organic compounds with known dissociation constants, that the spacing coefficient, 1+p, that characterizes the position of the n-th band as x_n ~ (1+p)^n, decreases with increasing dissociation constant, K_d. Theoretical arguments are developed to explain these experimental findings and to calculate explicitly the K_d dependence of 1+p.

cond-mat.stat-mech↗
arXiv1998

Derivation of the Matalon-Packter law for Liesegang patterns

Theoretical models of the Liesegang phenomena are studied and simple expressions for the spacing coefficients characterizing the patterns are derived. The emphasis is on displaying the explicit dependences on the concentrations of the inner- and the outer-electrolytes. Competing theories (ion-product supersaturation, nucleation and droplet growth, induced sol- coagulation) are treated with the aim of finding the distinguishing features of the theories. The predictions are compared with experiments and the results suggest that the induced sol-coagulation theory is the best candidate for describing the experimental observations embodied in the Matalon-Packter law.

cond-mat.soft↗
arXiv1998

Asymmetry studies in Lambda 0/Lambda 0-bar, Xi-/Xi+ and Omega-/Omega+ production

We present a study on hyperon/anti-hyperon production asymmetries in the framework of the recombination model. The production asymmetries for Lambda 0/Lambda 0-bar, Xi-/Xi+ and Omega-/Omega+ are studied as a function of x_F. Predictions of the model are compared to preliminary data on hyperon/anti-hyperon production asymmetries in 500 GeV/c pi- p interactions from the Fermilab E791 experiment. The model predicts a growing asymmetry with the number of valence quarks shared by the target and the produced hyperons in the x_F < 0 region. In the positive x_F region, the model predicts constant asymmetries for Lambda 0/Lambda 0-bar and Omega-/Omega+ production and a growing asymmetry with x_F for Xi-/Xi+. We found a qualitatively good agreement between the model predictions and data, showing that recombination is a competitive mechanism in the hadronization process.

hep-ph↗
arXiv1998

Lambda_c/Lambda_c-bar production asymmetries in pp and pi^- p collisions

We study Lambda_c/Lambda}_c-bar production asymmetries in pp and pi- p collisions using a recently proposed two component model. The model includes heavy baryon production by the usual mechanism of parton fusion and fragmentation plus recombination of valence and sea quarks from the beam and target hadrons. We compare our results with experimental data on asymmetries measured recently.

hep-ph↗
arXiv1997

D+- and D0 (anti D0) production asymetries in pion-proton collisions

We use a two-component model to describe the production mechanism of D mesons in pi-p collisions. The model combines the usual QCD processes plus fragmentation and recombination of charm that has been produced by nonperturbative QCD mechanisms. A hard charm component in the pion must be responsible of the particle anti-particle production asymmetries observed.

hep-ph↗