arXiv subjects

R. Alarcon

Publications and source records attributed to R. Alarcon.

43 records · Page 3Linked to original sources

arXiv2001

Relativistic effects and two-body currents in $^{2}H(\vec{e},e^{\prime}p)n$ using out-of-plane detection

Measurements of the ${^2}H(\vec{e},e^{\prime}p)n$ reaction were performed using an 800-MeV polarized electron beam at the MIT-Bates Linear Accelerator and with the out-of-plane magnetic spectrometers (OOPS). The longitudinal-transverse, $f_{LT}$ and $f_{LT}^{\prime}$, and the transverse-transverse, $f_{TT}$, interference responses at a missing momentum of 210 MeV/c were simultaneously extracted in the dip region at Q$^2$=0.15 (GeV/c)$^2$. On comparison to models of deuteron electrodisintegration, the data clearly reveal strong effects of relativity and final-state interactions, and the importance of the two-body meson-exchange currents and isobar configurations. We demonstrate that these effects can be disentangled and studied by extracting the interference response functions using the novel out-of-plane technique.

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arXiv2000

Search for Quadrupole Strength in the Electro-excitation of the Delta(1232)

High-precision H(e,e'p)pi0 measurements at Q2=0.126 (GeV/c)2 are reported, which allow the determination of quadrupole amplitudes in the gamma* N->Delta transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole amplitude ratios, Rsm=(-6.5 +- 0.2{stat+sys} +- 2.5{mod}) % and Rem=(-2.1 +- 0.2{stat+sys} +- 2.0{mod}) %, are dominated by model error. Previous Rsm and Rem results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account.

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arXiv1999

The Charge Form Factor of the Neutron from the reaction 2H(pol)(e(pol)e'n)p

We report on the first measurement of spin-correlation parameters in quasifree electron scattering from vector-polarized deuterium. Polarized electrons were injected into an electron storage ring at a beam energy of 720 MeV. A Siberian snake was employed to preserve longitudinal polarization at the interaction point. Vector-polarized deuterium was produced by an atomic beam source and injected into an open-ended cylindrical cell, internal to the electron storage ring. The spin correlation parameter $A^V_{ed}$ was measured for the reaction $^2 \vec{\rm H}(\vec e,e^\prime n)p$ at a four-momentum transfer squared of 0.21~(GeV/$c$)$^2$ from which a value for the charge form factor of the neutron was extracted.

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arXiv1999

The Charge Form Factor of the Neutron from the Reaction \pol{2H}(\pol{e},e'n)p

We report on the first measurement of spin-correlation parameters in quasifree electron scattering from vector-polarized deuterium. Polarized electrons were injected into an electron storage ring at a beam energy of 720~MeV. A Siberian snake was employed to preserve longitudinal polarization at the interaction point. Vector-polarized deuterium was produced by an atomic beam source and injected into an open-ended cylindrical cell, internal to the electron storage ring. The spin correlation parameter A^V_{ed} was measured for the reaction \pol{2H}(\pol{e},e'n)p at a four-momentum transfer squared of 0.21 (GeV/c)^2 from which a value for the charge form factor of the neutron was extracted.

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arXiv1998

Measurement of T20 in Elastic Electron-Deuteron Scattering

We report on a measurement of the tensor-analyzing power T20 in elastic electron-deuteron scattering in the range of four-momentum transfer from 1.8 to 3.2 fm-1. Electrons of 704 MeV were scattered from a polarized deuterium internal target. The tensor polarization of the deuterium nuclei was determined with an ion-extraction system, allowing an absolute measurement of T20. The data are described well by a non-relativistic calculation that includes the effects of meson-exchange currents.

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arXiv1998

Tensor Analyzing Powers for Quasi-Elastic Electron Scattering from Deuterium

We report on a first measurement of tensor analyzing powers in quasi-elastic electron-deuteron scattering at an average three-momentum transfer of 1.7 fm$^{-1}$. Data sensitive to the spin-dependent nucleon density in the deuteron were obtained for missing momenta up to 150 MeV/$c$ with a tensor polarized $^2$H target internal to an electron storage ring. The data are well described by a calculation that includes the effects of final-state interaction, meson-exchange and isobar currents, and leading-order relativistic contributions.

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arXiv1998

A Measurement of the Interference Structure Function, R_LT, for the 12C(e,e'p) reaction in the Quasielastic Region

The coincidence cross-section and the interference structure function, R_LT, were measured for the 12C(e,e'p) 11B reaction at quasielastic kinematics and central momentum transfer of q=400 MeV/c. The measurement was at an opening angle of theta_pq=11 degrees, covering a range in missing energy of E_m = 0 to 65 MeV. The R_LT structure function is found to be consistent with zero for E_m > 50 MeV, confirming an earlier study which indicated that R_L vanishes in this region. The integrated strengths of the p- and s-shell are compared with a Distorted Wave Impulse Approximation calculation. The s-shell strength and shape are compared with a Hartree Fock-Random Phase Approximation calculation. The DWIA calculation overestimates the cross sections for p- and s-shell proton knockout as expected, but surprisingly agrees with the extracted R_LT value for both shells. The HF-RPA calculation describes the data more consistently, which may be due to the inclusion of 2-body currents in this calculation.

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