0000000000072879
AUTHOR
D. J. Margaziotis
showing 15 related works from this author
Search for Effects Beyond the Born Approximation in Polarization Transfer Observables ine→pElastic Scattering
2011
Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, $$G_{E}/G_{M}$$, obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange (TPEX) contribution. In an effort to search for effects beyond the one-photon-exchange or Born approximation, we report measurements of polarization transfer observables in the elastic $$H(\vec{e},e'\vec{p})$$ reaction for three different beam energies at a fixed squared momentum transfer $Q^2 = 2.5$ GeV$^2$, spanning a wide range of the virtual photon p…
High Resolution Spectroscopy ofBΛ12by Electroproduction
2007
An experiment measuring electroproduction of hypernuclei has been performed in Hall A at Jefferson Lab on a $^{12}$C target. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A standard equipment. An unprecedented energy resolution of less than 700 keV FWHM has been achieved. Thus, the observed \lam{12}{B} spectrum shows for the first time identifiable strength in the core-excited region between the ground-state {\it s}-wave $\Lambda$ peak and the 11 MeV {\it p}-wave $\Lambda$ peak.
Virtual Compton scattering and the generalized polarizabilities of the proton atQ2=0.92and 1.76 GeV2
2012
Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P{sub LL}-P{sub TT}/epsilon and P{sub LT}, and the electric and magnetic generalized polarizabilities (GPs) alpha{sub E}(Q{sup 2}) and beta{sub M}(Q{sup 2}) at values of the four-momentum transfer squared Q{sup 2} = 0.92 and 1.76 GeV{sup 2}. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q{sup 2}-…
Measurement of the interference structure functionRLTfor the12C(e,e′p)reaction in the quasielastic region
1998
The coincidence cross section and the interference structure function, ${R}_{\mathrm{LT}},$ were measured for the ${}^{12}\mathrm{C}{(e,e}^{\ensuremath{'}}p){}^{11}\mathrm{B}$ reaction at quasielastic kinematics and central momentum transfer of $|\stackrel{\ensuremath{\rightarrow}}{q}|=400\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{c}.$ The measurement was at an opening angle of ${\ensuremath{\theta}}_{\mathrm{pq}}=11\ifmmode^\circ\else\textdegree\fi{},$ covering a range in missing energy of ${E}_{m}=0$ to 65 MeV. The ${R}_{\mathrm{LT}}$ structure function is found to be consistent with zero for ${E}_{m}g50\mathrm{MeV},$ confirming an earlier study which indicated that ${R}_{L}$ vanishes in this…
Measurement of the ExclusiveH3e(e,e′p)Reaction Below the Quasielastic Peak
2004
New, high-precision measurements of the 3He(e,ep) reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-ty…
Measurement of the Longitudinal, Transverse, and Longitudinal-Transverse Structure Functions in theH2(e,e′p)nReaction
1996
We have separated the longitudinal ({ital f}{sub 00}), transverse ({ital f}{sub 11}), and longitudinal-transverse interference ({ital f}{sub 01}) structure functions in the {sup 2}H({ital e},{ital e}{prime}{ital p}){ital n} reaction at {ital q}{searrow}{parallel}{approx_equal} 400 MeV/{ital c} and {omega}{approx_equal}110 MeV. A nonrelativistic calculation which includes effects due to final state interactions, meson exchange currents, and isobar configurations agrees with the measured {ital f}{sub 11} and {ital f}{sub 01} but overpredicts {ital f}{sub 00} by 25{percent} (2{sigma}). The data are also compared to the results of previous structure function measurements. {copyright} {ital 1996…
Out-of-plane measurements of the fifth response function of the exclusive electronuclear response
1999
The first measurements of f{sub LT}{sup '}, known as the fifth response function, have been made for the {sup 2}H(e(vector sign),e{sup '}p) and {sup 12}C(e(vector sign),e{sup '}p) reactions. This response is directly related to the imaginary part of the interference between the transverse and longitudinal nuclear electromagnetic currents. Its observation requires longitudinally polarized electron beams and out-of-plane detection, the latter made possible by the newly developed out-of-plane spectrometer system. The initial measurements were made by using a 560-MeV polarized electron beam and quasielastic kinematics at Q{sup 2}=3.3 fm{sup -2}. The development of the methodology for out-of-pla…
Rosenbluth Separation of the π^{0} Electroproduction Cross Section.
2016
We present deeply virtual $\pi^0$ electroproduction cross-section measurements at $x_B$=0.36 and three different $Q^2$--values ranging from 1.5 to 2 GeV$^2$, obtained from experiment E07-007 that ran in the Hall A at Jefferson Lab. The Rosenbluth technique was used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse component, and thus is far from the asymptotic limit predicted by perturbative Quantum Chromodynamics. An indication of a non-zero longitudinal contribution is provided by the interference term $\sigma_{LT}$ also measured. Results are compared with several models based on the leading twist approach of G…
A glimpse of gluons through deeply virtual compton scattering on the proton
2017
The internal structure of nucleons (protons and neutrons) remains one of the greatest outstanding problems in modern nuclear physics. By scattering high-energy electrons off a proton we are able to resolve its fundamental constituents and probe their momenta and positions. Here we investigate the dynamics of quarks and gluons inside nucleons using deeply virtual Compton scattering (DVCS)—a highly virtual photon scatters off the proton, which subsequently radiates a photon. DVCS interferes with the Bethe-Heitler (BH) process, where the photon is emitted by the electron rather than the proton. We report herein the full determination of the BH-DVCS interference by exploiting the distinct energ…
New Measurements of the Transverse Beam Asymmetry for Elastic Electron Scattering from Selected Nuclei
2012
We have measured the beam-normal single-spin asymmetry $A_n$ in the elastic scattering of 1-3 GeV transversely polarized electrons from $^1$H and for the first time from $^4$He, $^{12}$C, and $^{208}$Pb. For $^1$H, $^4$He and $^{12}$C, the measurements are in agreement with calculations that relate $A_n$ to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the $^{208}$Pb result is significantly smaller than the corresponding prediction using the same formalism. These results suggest that a systematic set of new $A_n$ measurements might emerge as a new and sensitive probe of the structure of heavy nuclei.
Backward electroproduction ofπ0mesons on protons in the region of nucleon resonances at four momentum transfer squaredQ2=1.0GeV2
2004
Exclusive electroproduction of pi{sup 0} mesons on protons in the backward hemisphere has been studied at Q2 = 1.0 GeV2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total (gamma*p) center-of-mass energy W from the pion production threshold to W = 2.0 GeV. The differential cross sections sigma{sub T} + epsilon sigma{sub L}, sigma{sub TL}, and sigma{sub TT} were separated from the azimuthal distribution and are presented together with the MAID and SAID parameterizations.
Virtual Compton Scattering and Neutral Pion Electroproduction in the Resonance Region up to the Deep Inelastic Region at Backward Angles
2009
We have made the first measurements of the virtual Compton scattering (VCS) process via the H$(e,e'p)\gamma$ exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the $W$-dependence at fixed $Q^2=1$ GeV$^2$, and for the $Q^2$-dependence at fixed $W$ near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed $Q^2$-dependence is smooth. The measured ratio of H$(e,e'p)\gamma$ to H$(e,e'p)\pi^0$ cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to Real Compton Scattering (RCS) at high energy and large angles, our VCS data…
Deeply virtual compton scattering off the neutron.
2007
The present experiment exploits the interference between the Deeply Virtual Compton Scattering (DVCS) and the Bethe-Heitler processes to extract the imaginary part of DVCS amplitudes on the neutron and on the deuteron from the helicity-dependent D$({\vec e},e'\gamma)X$ cross section measured at $Q^2$=1.9 GeV$^2$ and $x_B$=0.36. We extract a linear combination of generalized parton distributions (GPDs) particularly sensitive to $E_q$, the least constrained GPD. A model dependent constraint on the contribution of the up and down quarks to the nucleon spin is deduced.
Relativistic Effects and Two-Body Currents inH2(e→,e′p)nUsing Out-of-Plane Detection
2001
Measurements of the (2)H((-->)e,e(')p)n reaction were performed with the out-of-plane magnetic spectrometers (OOPS) at the MIT-Bates Linear Accelerator. The longitudinal-transverse, f(LT) and f(')(LT), and the transverse-transverse, f(TT), interference responses at a missing momentum of 210 MeV/c were simultaneously extracted in the dip region at Q2 = 0.15 (GeV/c)(2). In comparison to models of deuteron electrodisintegration, the data clearly reveal strong effects of relativity and final-state interactions and the importance of two-body meson-exchange currents and isobar configurations. We demonstrate that such effects can be disentangled by extracting these responses using the novel out-of…
Spectroscopy ofLiΛ9by electroproduction
2015
Background: In the absence of accurate data on the free two-body hyperon-nucleon interaction, the spectra of hypernuclei provides information on the details of the effective hyperon-nucleon interaction.Purpose: To obtain a high-resolution binding-energy spectrum for the ${}^{9}\mathrm{Be}(e,{e}^{\ensuremath{'}}{K}^{+})_{\ensuremath{\Lambda}}^{9}\mathrm{Li}$ reaction.Method: Electroproduction of the hypernucleus $_{\ensuremath{\Lambda}}^{9}\mathrm{Li}$ has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a $^{9}\mathrm{Be}$ target. In order to increase the counting rate and to provide unambiguous kaon identification, two superconducting septum magn…