Searcharxiv⌕ Search

arXiv subjects

M. Radici

Publications and source records attributed to M. Radici.

49 records · Page 3Linked to original sources
arXiv1999

Two-hadron interference fragmentation functions. Part II: a model calculation

We present a model calculation of leading order interference fragmentation functions arising from the distribution of two hadrons produced in the same jet of a fragmenting quark in a hard process. Using a simple spectator model for the mechanism of the hadronization process, for the first time we give a complete calculation and numerical estimates for the example of a proton-pion pair production with its invariant mass on the Roper resonance.

hep-ph↗
arXiv1999

Two-hadron interference fragmentation functions. Part I: general framework

We investigate the properties of interference fragmentation functions measurable from the distribution of two hadrons produced in the same jet in the current fragmentation region of a hard process. We discuss the azimuthal angular dependences in the leading order cross section of two-hadron inclusive lepton-nucleon scattering as an example how these interference fragmentation functions can be addressed separately.

hep-ph↗
arXiv1999

Interference Fragmentation Functions in Deep Inelastic Scattering

We give a general overview of the role and interpretation of fragmentation functions in hard processes. Transverse momentum dependence gives rise to time-reversal odd fragmentation functions contributing at leading order. Final state interactions are necessary to have non-zero time reversal odd functions. We present a model calculation for the special case of interference fragmentation functions in two-hadron inclusive lepton hadron scattering.

hep-ph↗
arXiv1998

Nucleon form factors in a chiral constituent-quark model

The electromagnetic form factors of the nucleon have been calculated in a chiral constituent-quark model. The nucleon wave functions are obtained by solving a Schrödinger-type equation for a semi-relativistic Hamiltonian with an effective interaction derived from the exchange of mesons belonging to the pseudoscalar octet and singlet and a linear confinement potential. The charge-density current operator has been constructed consistently with the model Hamiltonian in order to preserve gauge invariance and to satisfy the continuity equation.

hep-ph↗
arXiv1998

Semi-relativistic charge-current density operator

The charge-current density and two-photon operators consistent with a single-particle semi-relativistic Hamiltonian are derived within a suitable functional derivative formalism which preserves gauge invariance. An application to electron scattering is presented and results are compared with a fully relativistic case and the non-relativistic cases corrected through fourth order in M^{-1}.

nucl-th↗
arXiv1997

Nuclear transparency in quasielastic A(e,e'p): intranuclear cascade versus eikonal approximation

The problem of nuclear propagation through the nuclear medium in quasielastic A(e,e'p) reactions is discussed in the kinematic range 1<Q^2<7 (GeV/c)^2. The coefficient of nuclear transparency is calculated for each Q^2 in the framework of the intranuclear cascade model (INC) and of the eikonal approximation (EA). The predictions of both models are in good agreement with each other and with experimental data recently obtained at SLAC, BATES and TJNAF. The EA gives an explanation of the Q^2 behaviour of the transparency coefficient as a kinematic effect related to the superposition of contributions from each target shell.

nucl-th↗
arXiv1997

Helicity Asymmetry for Proton Emission from Polarized Electrons in the Eikonal Regime

The nuclear response to longitudinally polarized electrons, detected in coincidence with out-of-plane high-energy protons, is discussed in a simple model where the ejectile wave function is approximated as a plane wave with a complex wave vector. This choice is equivalent to solve the problem of Final-State Interactions (FSI) in homogeneous nuclear matter, as the residual nucleus can be described to a first approximation when dealing with very fast emitted protons. The main advantage of the present method is that in the framework of the Distorted-Wave Impulse Approximation (DWIA) it allows for an analytical derivation of all the components of the nuclear response. It emerges that cancellations among the leading contributions determine the very small absolute size of the socalled fifth structure function and produce a nontrivial asymptotic scaling of the related helicity asymmetry for large values of the momentum transfer.

nucl-th↗
arXiv1996

High-momentum proton removal from 16O and the (e,e'p) cross section

The cross section for the removal of high-momentum protons from 16O is calculated for high missing energies. The admixture of high-momentum nucleons in the 16O ground state is obtained by calculating the single-hole spectral function directly in the finite nucleus with the inclusion of short-range and tensor correlations induced by a realistic meson-exchange interaction. The presence of high-momentum nucleons in the transition to final states in 15N at 60-100 MeV missing energy is converted to the coincidence cross section for the (e,e'p) reaction by including the coupling to the electromagnetic probe and the final state interactions of the outgoing proton in the same way as in the standard analysis of the experimental data. Detectable cross sections for the removal of a single proton at these high missing energies are obtained which are considerably larger at higher missing momentum than the corresponding cross sections for the p-wave quasihole transitions. Cross sections for these quasihole transitions are compared with the most recent experimental data available.

nucl-th↗
arXiv1996

Angular Distributions for Knockout and Scattering of Protons in the Eikonal Approximation

The advent of new electron accelerators with few-GeV beam energies makes the (e,e'p) reaction a promising tool for investigating new aspects of the electromagnetic interaction. To this purpose it is crucial to set the scale of Final-State Interactions (FSI) at high ejectile energies. We have analyzed the constraints which allow for a meaningful generalization to (e,e'p) of the Glauber method used in elastic (p,p) scattering. The FSI dominance at large deflection angles produces in the distributions a universal behaviour resembling the coherent diffractive scattering between the ejected proton and the (residual) nucleus. It is argued that the comparison between (e,e'p) and (p,p), when a meaningful one, may represent a convenient tool to disentangle (exotic) effects due to FSI from those related to the (hard) electromagnetic vertex.

nucl-th↗
arXiv1995

The (e,e'p) Reaction and the Transition to the Eikonal Regime

The reliability of the models describing the Final-State Interactions (FSI) in (e,e$'$p) scattering at high proton energies is an important issue in view of the experiments planned at CEBAF. One of the most popular approaches adopted, the Glauber method, involves the linearization of the wave equation for the ejected proton travelling through the residual nucleus. We have studied the consequences of such an assumption for the case of the $^{12}\mathrm{C(e,e}'\mathrm{p)}^{11}\hbox{\rm B}^*$ reaction at high proton momenta by comparing the results with the predictions obtained when the second-order differential equation for the proton wave is solved exactly for each partial wave. We find that the two methods give well-correlated angular distributions for momenta in the range 1-4 GeV/c, i.e. for kinematics relevant to the transition to the eikonal regime.

nucl-th↗
arXiv1995

A Test of the Eikonal Approximation in High-Energy (e,e'p) Scattering

The Glauber method is extensively used to describe the motion of a hadronic projectile in interaction with the surrounding nuclear medium. One of the main approximations consists in the linearization of the wave equation for the interacting particle. We have studied the consequences of such an assumption in the case of the $^{12}\mathrm{C(e,e}'\mathrm{p)}^{11}\hbox{\rm B}^*$ reaction at high proton momenta by comparing the results with the predictions obtained when all the ingredients of the calculation are unchanged but the second-order differential equation for the scattered wave, which is solved exactly for each partial wave up to a maximum of 120 spherical harmonics. We find that the Glauber cross section is always larger by a factor $10 ÷20 \%$, even at vanishing missing momenta. We give a quantum-mechanical explanation of this discrepancy. Nevertheless, a good correlation is found between the two predictions as functions of the missing momentum, especially in parallel kinematics.

nucl-th↗
arXiv1994

Many-body effects in 16O(e,e'p)

Effects of nucleon-nucleon correlations on exclusive $(e,e'p)$ reactions on closed-shell nuclei leading to single-hole states are studied using $^{16}O(e,e'p)^{15}N$ ($6.32$ MeV, $3/2^-$) as an example. The quasi-hole wave function, calculated from the overlap of translationally invariant many-body variational wave functions containing realistic spatial, spin and isospin correlations, seems to describe the initial state of the struck proton accurately inside the nucleus, however it is too large at the surface. The effect of short-range correlations on the final state is found to be largely cancelled by the increase in the transparency for the struck proton. It is estimated that the values of the spectroscopic factors obtained with the DWIA may increase by a few percent due to correlation effects in the final state.

nucl-th↗