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Xavier Artru

Publications and source records attributed to Xavier Artru.

17 recordsLinked to original sources
arXiv2025

A model for baryon production in spin-dependent string fragmentation

We introduce spin-1/2 baryons in the string+${}^3P_0$ model of hadronization, previously restricted to the production of pseudoscalar and vector mesons. Baryons are modeled as quark-diquark bound states and baryon production is described by the tunneling of diquark-antidiquark pairs at string breaking points. Diquarks can be scalar or pseudovector, the latter being produced in the relative ${}^5D_0$ state. Introducing the quark-baryon-diquark coupling, the relevant splitting amplitudes for the emission of baryons are constructed and used to explore analytically the model predictions. We find a Collins effect for baryon production in the fragmentations of transversely polarized quarks or diquarks as well as a baryon spontaneous transverse polarization. The hadronic decays of polarized hyperons are also included in the model, which is presented in a form suitable for the implementation in a Monte Carlo event generator.

hep-ph↗
arXiv2022

Simulation of the Polarized Quark Fragmentation with Vector Meson Production

The recently developed quantum mechanical string+${}^3P_0$ model of polarized quark fragmentation with pseudoscalar and vector meson production has been implemented in a stand alone Monte Carlo program. The simulation enables the detailed study of the quark spin dependent effects in the fragmentation process such as the transverse spin asymmetries. In particular, it allows to investigate the effects of the production and decay of vector mesons on the Collins and dihadron asymmetries of the observed hadrons, and to study the still unknown Collins effect for vector mesons. The main results of the Monte Carlo simulations obtained so far are summarized and the comparison with the existing experimental data on SIDIS and $e^+e^-$ annihilation to hadrons processes are presented.

hep-ph↗
arXiv2022

The String+${}^3P_0$ Model of Hadronization

We present the main theoretical aspects of the quantum mechanical string+${}^3P_0$ model of polarized quark fragmentation for pseudoscalar and vector meson production. The model is an extension of the Lund string fragmentation model that systematically includes the quark spin degree of freedom assuming the ${}^3P_0$ mechanism of quark pair production at string breaking. The recently achieved introduction of vector mesons accounts for the spin correlations between the latter and the quark of the fragmentation chain. The string+${}^3P_0$ model reproduces transverse spin effects such as the Collins effect and the dihadron asymmetry, and longitudinal spin effects such as the jet handedness.

hep-ph↗
arXiv2020

Quantum versus classical approach of dechanneling and incoherent electromagnetic processes in aligned crystals

Particles traveling in aligned crystals at small angles w.r.t. crystallographic axes or planes are principally steered by the continuous Lindhard potential. This interaction conserves the energy E, the longitudinal momentum p_parallel, the transverse energy of the particle E_perp and is elastic concerning the crystal quantum state. At high enough energy the particle motion is quasi-classical. The time-dependent fluctuations of the positions of the atoms or of the electrons of the crystal create a residual potential, on which the particle can scatter. This interaction does not conserve the previous quantities and is inelastic for the crystal. We compare its treatments with the classical binary collision model and with a phenomenological quantum model. The classical dechanneling rate is estimated to be several ten per cent larger than the quantum one. The influence of correlated vibrations of neighboring atoms is discussed.

quant-ph↗
arXiv2020

Classical spectral sum rules and "half-naked" electron effects in radiation from relativistic electrons in external field

Two properties of the radiation emitted by a relativistic electron in an external field, in the classical approximation, are presented in details: 1) spectral sum rules and their relationship with the sum rules for oscillator strength in atomic physics. Filtered sum rules can be used to remove infrared or ultraviolet divergences. 2) "half-naked electron" effects like the Landau- Pomeranchuk-Migdal and Ternovskij-Shul'ga-Fomin effects. These properties are best understood when introducing the apparent transverse velocity.

hep-ph↗
arXiv2014

Classical and Quantum Phenomenology in Radiation by Relativistic Electrons in Matter or in External Fields

Phenomenological aspects of radiation by relativistic electrons in external field, in matter or the vicinity of matter are reviewed, among which: infrared divergence, coherence length effects, shadowing, enhancement in aligned crystals, quantum recoil and spin effects, electron side-slipping, photon impact parameter and the presence of tunnelling in the radiation process.

physics.acc-ph↗
arXiv2014

Transverse momentum asymmetry of the extracted electron in field ionization of a Hydrogen Atom with angular momentum

The tunneling ionization of a hydrogen atom excited in the presence of a static electric field is investigated for the case where, before being extracted, the electron has an orbital angular momentum L perpendicular to the field E. The escaping electron has a nonzero mean transverse velocity in the direction of E cross . This asymmetry is similar to the Collins effect in the fragmentation into hadrons of a transversely polarized quark. In addition, the linear Stark effect make and oscillate in time. The degree of asymmetry is calculated at leading order in E for an initial state of maximum transverse . The conditions for the observation of this asymmetry are discussed.

physics.atom-ph↗
arXiv2008

Constraints on spin observables

Positivity constrains the allowed domain for sets of spin observables in exclusive or inclusive reactions. Examples are given for strangeness-echange reactions and photoproduction.

nucl-th↗
arXiv2008

Spin observables and spin structure functions: inequalities and dynamics

Model-independent identities and inequalities relating the various spin observables of a reaction are reviewed in a unified formalism, together with their implications for dynamical models, their physical interpretation, and the quantum aspects of the information carried by spins, in particular entanglement. These constraints between observables can be obtained from the explicit expression of the observables in terms of a set of amplitudes, a non-trivial algebraic exercise which can be preceded by numerical simulation with randomly chosen amplitudes, from anticommutation relations, or from the requirement that any polarisation vector is less than unity. The most powerful tool is the positivity of the density matrices describing the reaction or its crossed channels, with a projection to single out correlations between two or three observables. For the exclusive reactions, the cases of the strangeness-exchange proton-antiproton scattering and the photoproduction of pseudoscalar mesons are treated in some detail: all triples of observables are constrained, and new results are presented for the allowed domains. The positivity constraints for total cross-sections and single-particle inclusive reactions are reviewed, with application to spin-dependent structure functions and parton distributions. The corresponding inequalities are shown to be preserved by the evolution equations of QCD.

hep-ph↗
arXiv2007

Positivity Constraints on Spin Observables in Exclusive Pseudoscalar Meson Photoproduction

Positivity constraints have proved to be important for spin observables of exclusive reactions involving polarized initial and final particles. Attention is focused in this note on the photoproduction of pseudoscalar mesons from spin 1/2 baryons, more specifically gamma+ N -> K+ Lambda, gamma+ N -> K Sigma, for which new experimental data are becoming available.

nucl-th↗
arXiv2002

The Transverse Spin

Contents : 1. Pre-history 2. Transversity versus helicity 3. The massless limit. "Cardan" and "see-saw" transformations 4. Transversity distribution delta q(x). The diquark spectator model 5. Soffer inequality 6. Tensor charge sum rule 7. t-channel analysis 8. Selection rules for delta q(x) measurements 9. Evolution with Q squared 10. Quark polarimetry. The sheared-jet (Collins) effect 11. Single-spin asymmetries in inclusive experiments 12. Quark distribution dependent on both spin and transverse momentum 13. First evidence of quark transversity

hep-ph↗
arXiv2002

Bunch coherence in parametric X-ray radiation

The amplitude of Parametric X-ray radiation emitted coherently by a bunch of electrons crossing a crystal (CPXR) is calculated. When the bunch density is modulated with a longitudinal period close to the X-ray wavelenght, constructive many-electron interferences enhance the intensity by Nb * |F(K)|^2, where Nb is the number of electrons in the bunch, F(K) the bunch form factor and K a specified wave vector. CPXR can be used to test the microbunching in a X-ray free-electron laser.

physics.acc-ph↗
arXiv2002

Dynamics of a magnetic monopole in matter, Maxwell equations in dyonic matter and detection of electric dipole moments

For a monopole, the analogue of the Lorentz equation in matter is shown to be f = g (H - v cross D). Dual-symmetric Maxwell equations, for matter containing hidden magnetic charges in addition to electric ones, are given. They apply as well to ordinary matter if the particles possess T-violating electric dipole moments. Two schemes of experiments for the detection of such moments in macroscopic pieces of matter are proposed.

physics.gen-ph↗
arXiv2002

Side-slipping of a radiating particle

Radiation reaction is revisited, first in a new classical aproach, where the physical particle 4-momentum is redefined as the energy-momentum flux across the future light cone and is not parallel to the 4-velocity. Then in a semi-classical approach, it is shown that, when emitting a photon, the particle "side-slips" transversaly to its initial momentum, justifying the non-colinearity between momentum and mean velocity. Side-slipping is finally checked in a pure quantum mechanical treatment of synchrotron radiation.

physics.class-ph↗
arXiv1995

Measuring transverse spin correlations by 4-particle correlations in $e^+ e^-\to 2 \ {\rm jets}$

The azimuthal distribution of pairs of particles in a jet is sensitive to the transverse polarization of the quark initiating the jet, but with a sensitivity that involves a nonperturbative analyzing power. We show in detail how to measure the analyzing power from 4-hadron correlations in $e^+ e^- \to 2 \ {\rm jets}$. We explain the combinations of particle flavor that are likely to give the biggest effect.

hep-ph↗