arXiv subjects

S. Jeschonnek

Publications and source records attributed to S. Jeschonnek.

16 recordsLinked to original sources

arXiv2014

Deuteron Electro-Disintegration at Very High Missing Momenta

We propose to measure the D(e,e'p) cross section at $Q^2 = 4.25$ (GeV/c)$^2$ and $x_{bj} = 1.35$ for missing momenta ranging from $p_m = 0.5$ GeV/c to $p_m = 1.0$ GeV/c expanding the range of missing momenta explored in the Hall A experiment (E01-020). At these energy and momentum transfers, calculations based on the eikonal approximation have been shown to be valid and recent experiments indicated that final state interactions are relatively small and possibly independent of missing momenta. This experiment will provide for the first time data in this kinematic regime which are of fundamental importance to the study of short range correlations and high density fluctuations in nuclei. The proposed experiment could serve as a commissioning experiment of the new SHMS together with the HMS in Hall C. A total beam time of 21 days is requested.

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arXiv2009

A Precise Measurement of the Neutron Magnetic Form Factor GMn in the Few-GeV2 Region

The neutron elastic magnetic form factor GMn has been extracted from quasielastic electron scattering data on deuterium with the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic coverage of the measurement is continuous from Q2=1 GeV2 to 4.8 GeV2. High precision was achieved by employing a ratio technique in which many uncertainties cancel, and by a simultaneous in-situ calibration of the neutron detection efficiency, the largest correction to the data. Neutrons were detected using the CLAS electromagnetic calorimeters and the time-of-flight scintillators. Data were taken at two different electron beam energies, allowing up to four semi-independent measurements of GMn to be made at each value of Q2. The dipole parameterization is found to provide a good description of the data over the measured Q2 range.

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arXiv2008

Faddeev and Glauber Calculations at Intermediate Energies in a Model for n+d Scattering

Obtaining cross sections for nuclear reactions at intermediate energies based on the Glauber formulation has a long tradition. Only recently the energy regime of a few hundred MeV has become accessible to ab-initio Faddeev calculations of three-body scattering. In order to go to higher energies, the Faddeev equation for three-body scattering is formulated and directly solved without employing a partial wave decomposition. In the simplest form the Faddeev equation for interacting scalar particles is a three-dimensional integral equation in five variables, from which the total cross section, the cross sections for elastic scattering and breakup reactions, as well as differential cross sections are obtained. The same observables are calculated based on the Glauber formulation. The first order Glauber calculation and the Glauber rescattering corrections are compared in detail with the corresponding terms of the Faddeev multiple scattering series for projectile energies between 100 MeV and 2 GeV.

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arXiv2001

The quasielastic 2H(e,e'p)n reaction at high recoil momenta

The 2H(e,e'p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility (JLab) in quasielastic kinematics (x=0.96) at a four-momentum transfer squared, Q^2=0.67 (GeV/c)^2. The experiment was performed in fixed electron kinematics for recoil momenta from zero to 550 MeV/c. Though the measured cross section deviates by 1-2 sigma from a state-of-the-art calculation at low recoil momenta, it agrees at high recoil momenta where final state interactions (FSI) are predicted to be large.

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arXiv2001

Quark-Hadron Duality in Structure Functions

While quark-hadron duality is well-established experimentally, the current theoretical understanding of this important phenomenon is quite limited. To expose the essential features of the dynamics behind duality, we use a simple model in which the hadronic spectrum is dominated by narrow resonances made of valence quarks. We qualitatively reproduce the features of duality as seen in electron scattering data within our model. We show that in order to observe duality, it is essential to use the appropriate scaling variable and scaling function. In addition to its great intrinsic interest in connecting the quark-gluon and hadronic pictures, an understanding of quark-hadron duality could lead to important benefits in extending the applicability of scaling into previously inaccessible regions.

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arXiv1999

Origin of Relativistic Effects in the Reaction D(e,e'p)n at GeV Energies

In a series of recent publications, a new approach to the non-relativistic reduction of the electromagnetic current operator in calculations of electro-nuclear reactions has been introduced. In one of these papers, the conjecture that at energies of a few GeV, the bulk of the relativistic effects comes from the current and not from the nuclear dynamics was made, based on the large relativistic effects in the transverse-longitudinal response. Here, we explicitly compare a fully relativistic, manifestly covariant calculation performed with the Gross equation, with a calculation that uses a non-relativistic wave function and a fully relativistic current operator. We find very good agreement up to missing momenta of 400 MeV/c, thus confirming the previous conjecture. We discuss slight deviations in cross sections for higher missing momenta and their possible origin, namely p-wave contributions and off-shell effects.

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arXiv1999

Spin-orbit final state interaction in the framework of Glauber theory for (e,e'p) reactions

We investigate the reactions D(e,e'p)n and D(\vec e,e'p)n at GeV energies and discuss the opportunities to distinguish between different models for the nuclear ground state by measuring the response functions. In calculating the final-state interaction (FSI) we employ Glauber theory, and we also include relativistic effects in the electromagnetic current. We include not only the central FSI, but also the spin-orbit FSI which is usually neglected in (e,e'p) calculations within the Glauber framework and we show that this contribution plays a crucial role for the fifth response function. All of the methods developed here can be applied to any target nucleus.

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arXiv1997

Relativistic Effects in the Electromagnetic Current at GeV Energies

We employ a recent approach to the non-relativistic reduction of the electromagnetic current operator in calculations of electronuclear reactions. In contrast to the traditional scheme, where approximations are made for the transferred momentum, transferred energy and initial momentum of the struck nucleon in obtaining an on-shell inspired form for the current, we treat the problem exactly for the transferred energy and transferred momentum. We calculate response functions for the reaction $^2H(e,e'p)n$ at CEBAF (TJNAF) energies and find large relativistic corrections. We also show that in Plane Wave Impulse Approximation, it is always possible to use the full operator, and we present a comparison of such a limiting case with the results incorporating relativistic effects to the first order in the initial momentum of the struck nucleon.

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arXiv1996

Final State Charge Exchange Interactions in the $^{12}C(e,e'p)$ Reaction

The $^{12}C(e,e'p)$ reaction is analyzed in a model which explicitly includes final state interactions due to the coupling of the proton and neutron emission channels. We find that the effects of the final state interactions due to charge exchange reactions are important to get a good description of the symmetry properties of the recently measured Mainz spectral functions. We discuss the possible role the off-shell effects may play for the correct interpretation of spectral functions at large positive missing momenta.

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arXiv1995

Universal pattern in (e,e'p) at large missing momenta: quasi-deuteron or diffractive final state interactions?

The intrinsic single particle momentum distributions in nuclei are supposed to show a universal behavior at large momenta, dominated by short-range correlated pairs, or quasi-deuterons. We discuss whether the quasi-deuteron universality survives the final state interaction effects, which are present in the missing momentum spectra measured in $A(e,e'p)$ experiments at GeV energies. We demonstrate that in the observed missing momentum spectra an approximate universality is present, but originating from the universal pattern of diffractive final state interactions of the struck proton independent of the target nucleus.

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arXiv1995

Do final state interactions obscure short range correlation effects in quasielastic $A(e,e'p)$ scattering?

Are short range correlations in the ground state of the target nucleus (initial state correlations ISC)observable inexperiments on quasielastic $A(e,e'p)$ scattering at large missing momentum $p_{m}$? Will the missing momentum spectrum observed at CEBAF be overwhelmed by final state interactions of the struck proton? Taking the $^{4}He$ nucleus with a realistic model wave function for a testing ground, we present a full calculation of the missing momentum distribution in inclusive $^{4}He(e,e'p)$ scattering. We find a complex interplay and strong quantum-mechanical interference of FSI and ISC contributions to scattering at large $p_{m}$, with drastic change of the interference pattern from the (anti)parallel to transverse kinematics. We show that in all the kinematical conditions, for missing momenta $p_{m}\gsim 1$\,fm$^{-1}$, quasielastic scattering is dominated by FSI effects and the sensitivity to details of the nuclear ground state is lost. The origin of the FSI dominance is well understood and can be traced back to the anisotropic behaviour of FSI which is long ranged in the longitudinal direction and short ranged in the transverse direction in the opposite to the short ranged ground state correlations.

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arXiv1995

Final state interactions and $NN$ correlations: are the latter observable?

Are effects of short range correlations in the ground state of the target nucleus (initial state correlations ISC) observable in experiments on quasielastic $A(e,e'p)$ scattering at large missing momentum $p_{m}$? Will the missing momentum spectrum observed at CEBAF be overwhelmed by final state interactions (FSI) of the struck proton? The recent advances in the theory of FSI and findings of complex interplay and strong quantum-mechanical interference of FSI and ISC contributions to scattering at $p_{m}\gsim 1$\,fm$^{-1}$ are reviewed. We conclude that for $p_m \gsim 1$ \, fm$^{-1}$ quasielastic scattering is dominated by FSI effects and the sensitivity to details of the nuclear ground state is lost.

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arXiv1995

Quadrupole deformation of deuterons and final state interaction in $^2 \vec H (e,e'p)$ scattering on tensor polarized deuterons at CEBAF energies

The strength of final state interaction (FSI) between struck proton and spectator neutron in $^2\vec{H}(e,e'p)$ scattering depends on the alignment of the deuteron. We study the resulting FSI effects in the tensor analyzing power in detail and find substantial FSI effects starting at still low missing momentum $p_m \gsim 0.9 fm^{-1}$. At larger $p_m \gsim 1.5 fm^{-1}$, FSI completely dominates both missing momentum distribution and tensor analyzing power. We find that to a large extent FSI masks the sensitivity of the tensor analyzing power to models of the deuteron wave function. For the transversely polarized deuterons the FSI induced forward-backward asymmetry of the missing momentum distribution is shown to have a node at precisely the same value of $p_m$ as the PWIA missing momentum distribution. The position of this node is not affected by FSI and can be a tool to distinguish experimentally between different models for the deuteron wave function.

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arXiv1994

The apparent Coulomb reacceleration of neutrons in electrodissociation of the deuteron

We demonstrate that the final state $p$-$n$ interaction in the reaction of electrodissociation of the deuteron at large $Q^{2}$ in a static external field leads to the apparent reacceleration of neutrons. The shift of the neutron velocity from the velocity of the deuteron beam is related to the quantum-mechanical forward-backward asymmetry of the missing momentum distribution in the $^2H(e,e'p)n$ scattering.

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arXiv1994

Final state interaction effects in $D(e,e'p)$ scattering

We present a systematic study of the final-state interaction (FSI) effects in $D(e,e'p)$ scattering in the CEBAF energy range with particular emphasis on the phenomenon of the angular anisotropy of the missing momentum distribution. We find that FSI effects dominate at missing momentum $p_m \gsim 1.5 $fm$^{-1}$. FSI effects in the excitation of the $S$-wave state are much stronger than in the excitation of the $D$-wave.

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arXiv1994

Simple classification of final state interaction effects in $^4He(e,e'p)$ scattering

The radius of interaction between the struck proton and spectator nucleons is close to the radius of short-distance two-nucleon correlations in nuclear matter, which makes final state interaction(FSI) an important background to production of protons with large missing momentum. We present a simple classification of the dominant FSI effects in $^4He(e,e'p)$ scattering and identify parts of the phase space dominated by FSI. At large missing momentum, FSI leads to a striking angular anisotropy of the missing momentum distribution, which has a prominent peak in transverse kinematics and smaller, forward-backward asymmetric, peaks in parallel kinematics.

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