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 H͑e, e 0 n͒ p at a four-momentum transfer squared of 0.21 ͑GeV͞c͒ 2 from which a value for the charge form factor of the neutron was extracted. [S0031-9007(99)09392-8] PACS numbers: 13.40. Gp, 14.20.Dh, 24.70. + s, 25.30.Fj Although the neutron has no net electric charge, it does have a charge distribution. Precise measurements [1] where thermal neutrons from a nuclear reactor are scattered from atomic electrons indicate that the neutron has a positive core surrounded by a region of negative charge. The actual distribution is described by the charge form factor G n E , which enters the cross section for elastic electron scattering. It is related to the Fourier transform of the charge distribution and is generally expressed as a function of Q 2 , the square of the four-momentum transfer. Data on G n E are important for our understanding of the nucleon and are essential for the interpretation of electromagnetic multipoles of nuclei, e.g., the deuteron.Since a practical target of free neutrons is not available, experimentalists mostly resorted to (quasi)elastic scattering of electrons from unpolarized deuterium [2,3] to determine this form factor. The shape of G n E as a function of Q 2 is relatively well known from high precision elastic electron-deuteron scattering [3]. However, in this case the cross section is dominated by scattering from the proton and, moreover, is sensitive to nuclear-structure uncertainties and reaction-mechanism effects. Consequently, the absolute scale of G n E still contains a systematic uncertainty of about 50%.Many of the aforementioned uncertainties can be significantly reduced through the measurement of electronuclear spin observables. The scattering cross section with both longitudinal polarized electrons and a polarized target for the 2 H͑e, e 0 N͒ reaction, can be written as [4]where S 0 is the unpolarized cross section, h the polarization of the electrons, and P d 1 (P d 2 ) the vector (tensor) polarization of the target. A e is the beam analyzing power, A V ͞T d the vector and tensor analyzing powers, and A V ͞T ed the vector and tensor spin-correlation parameters. The target analyzing powers and spin-correlation parameters depend on the orientation of the target spin. The polarization direction of the deuteron is defined by the angles Q d and F d in the frame where the z axis is along the direction of the three-momentum transfer (q) and the y axis is defined by the vector product of the incoming and outgoing electron momenta. A V ed ͑Q d 90 ±...

We report on a measurement of the tensor analyzing power T20 in elastic electron-deuteron scattering in the range of fourmomentum 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 mesonexchange currents.PACS numbers: 13.40. Gp, 21.45.+v, 25.30.Bf, 29.25.Pj The deuteron, as the simplest nucleus, serves as a sensitive testing ground for a variety of nuclear models (nonrelativistic [1,2], fully covariant [3,4]). The charge and current distributions inside the nucleus can be probed with elastic electron scattering at intermediate energies.Elastic electron scattering off the spin-1 deuteron is completely described in terms of three electro-magnetic form factors: the charge monopole G C , the magnetic dipole G M and the charge quadrupole G Q . Measurement of the unpolarized cross section yields the structure functions A(G C ,G M ,G Q ) and B(G M ). When the tensor analyzing power T 20 is also determined, all three form factors can be separated [5]. A large body of data is available for A and B for values of the four-momentum transfer Q of up to 12 fm −1 , while T 20 has been measured up to 4 fm −1 , albeit with limited accuracy. The observable T 20 contains an interference between G C and G Q and is thus sensitive to the effects of short-range and tensor correlations in the ground-state wave function of the deuteron. In this paper absolute measurements are presented on the analyzing powers in the ↔ 2 H(e,e ′ d)-reaction for Q-values between 1.8 and 3.2 fm −1 with a high accuracy.The cross section for elastic electron-deuteron scattering with unpolarized electrons and tensor-polarized deuterium nuclei can be expressed as [5] with σ 0 the unpolarized cross section, T 2i the tensor analyzing powers and P zz the degree of tensor polarization. The polarization axis of the deuteron is defined by the angles θ * and φ * in the frame where the z-axis is along the direction of the three-momentum transfer q and the x-axis is perpendicular to z in the scattering plane. The experiment was performed using a 704 MeV electron beam in the AmPS storage ring [6] and a tensorpolarized deuterium internal target [7] at NIKHEF. By stacking several pulses of electrons, produced by the medium-energy accelerator, circulating currents of up to 150 mA were stored in the ring. A beam life time in excess of 2000 s was obtained by compensating synchrotron radiation losses with a 476 MHz cavity.Nuclear-polarized deuterium gas was provided by an atomic beam source. Deuterium atoms are produced by means of an RF dissociator. Atoms with their electron spin up are focused into the target-cell feed tube by two sextupole magnets, whereas those with spin down are defocused. A medium-and a strong-field RF-unit induce transitions between the hyperfine states, resulting in...

We report an absolute measurement of the tensor analyzing powers T 20 and T 22 in elastic electrondeuteron scattering at a momentum transfer of 1.6 fm 21 . The novel approach of this measurement is the use of a tensor polarized 2 H target internal to an electron storage ring, with in situ measurement of the polarization of the target gas. Scattered electrons and recoil deuterons were detected in coincidence with two large acceptance nonmagnetic detectors. The techniques demonstrated have broad applicability to further measurements of spin-dependent electron scattering.[ S0031-9007(96) Measurements of spin-dependent electron scattering have the potential to greatly enhance our understanding of nucleon and nuclear structure. For example, spin observables in elastic, quasielastic, and deep-inelastic scattering from polarized deuterium are predicted to provide important information on the effects of D-wave components in the ground state of 2 H [1], the largely unknown charge form factor of the neutron [2], and the neutron spin structure functions [3]. This has prompted development of both polarized 2 H targets for use with internal [4] or external beams [5] and polarimeters for measuring the polarization of recoiling hadrons [6]. Indeed the first round of measurements of spin-dependent e-2 H scattering has been carried out at Novosibirsk [7,8], Bonn [9], MITBates [10,11], and SLAC [12].The measurement of analyzing powers and spincorrelation parameters in spin-dependent electron scattering from polarized nuclei is optimally performed by scattering electrons from a pure and highly polarized target. Polarized internal gas targets in electron storage rings have the advantage that spin-dependent scattering from chemically and isotopically pure atomic species of high polarization can be realized. They offer rapid polarization reversal and flexible orientation of the nuclear spin direction by using low magnetic holding fields, a low thickness at high luminosity which allows for the detection of low-energy recoiling hadrons, and access to a broad kinematic range by using large acceptance detectors. For polarized deuterium one has the additional ability to reverse the tensor polarization, P zz , at fixed vector polarization, P z , and vice versa. Subsequently, small systematic errors can be expected.The first pioneering measurements [7,8] with a polarized deuterium internal target have been carried out at VEPP-3 in Novosibirsk. They realized a target with a thickness limited to about 3 3 10 11 atoms cm 22 [8] as viewed by their detectors. Recently, this was increased by an order of magnitude [13]. Since many mechanisms can depolarize the target nuclei in the storage cell, and no polarimeters were available to measure the target polarization in situ, they normalized one datum to a theoretical prediction, setting the scale for the other data points [8].The electron spin-averaged cross section for elastic electron-deuteron scattering can be expressed [1] as s s 0

The spin-momentum correlation parameter A V ed was measured for the 2 H͑e, e 0 p͒n reaction for missing momenta up to 350 MeV͞c at Q 2 0.21 ͑GeV͞c͒ 2 for quasielastic scattering of polarized electrons from vector-polarized deuterium. The data give detailed information about the deuteron spin structure and are in good agreement with the results of microscopic calculations based on realistic nucleon-nucleon potentials and including various spin-dependent reaction mechanism effects. The experiment reveals in a most direct manner the effects of the D state in the deuteron ground-state wave function and shows the importance of isobar configurations for this reaction. DOI: 10.1103/PhysRevLett.88.102302 PACS numbers: 25.30.Fj, 21.45. +v, 24.70. +s, 27.10. +h The deuteron serves as a benchmark for testing nuclear theory. Observables such as its binding energy, static magnetic dipole and charge quadrupole moment, asymptotic D͞S ratio, and the elastic electromagnetic form factors place strong constraints on any realistic nuclear model. Its simple structure allows reliable calculations to be performed in both nonrelativistic and relativistic frameworks [1 -6]. Such calculations are based upon state-of-the-art nucleon-nucleon (NN) potentials [7][8][9][10], and the resulting ground-state wave function is dominated by the S state, especially at low relative proton-neutron momentum p in the center of mass system. Because of the tensor part of the NN interaction a D-state component is generated (see, e.g., [5,11]). The models predict that the S-and D-state components strongly depend on p and are sensitive to the repulsive core of the NN interaction at short distances [5].Traditionally, the spin structure of the deuteron has been studied through measurements of the tensor analyzing power T 20 [12][13][14][15][16][17][18] in elastic electron-deuteron scattering. Complementary information can be obtained by electrodisintegration studies in the region of quasielastic scattering. In the 2 H͑e, e 0 p͒n reaction, energy n and three-momentum q are transferred to the nucleus and the nuclear response can be mapped as a function of missing momentum p m and missing energy. Here, p m ϵ q 2 p f and p f represents the momentum of the ejected proton. In the planewave impulse approximation (PWIA) the neutron is a spectator only during the scattering process, and p m is equal to the initial proton momentum in the deuteron, while the missing energy equals the binding energy. In this way the ͑e, e 0 p͒ reaction has been employed to probe the proton inside the deuteron for momenta up to 1.0 GeV͞c [19][20][21].To enhance the sensitivity to the spin structure of the deuteron, spin dependent observables in quasielastic scattering can be used [5,22,23]. The polarization of a proton P p z inside a deuteron with a vector polarization P d 1 , is given by [24]where P S and P D , respectively, represent the S-and D-state probability densities of the ground-state wave function. Note that the polarization of a nucleon in the D state is opposite to that of...

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We report on a first measurement of tensor analyzing powers in quasielastic electron-deuteron scattering at an average three-momentum transfer of 1.7 fm 21 . Data sensitive to the spin-dependent nucleon density in the deuteron were obtained for missing momenta up to 150 MeV͞c 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. [S0031-9007(98) The deuteron is often used as a benchmark to test nuclear theory, since reliable calculations can be performed in both nonrelativistic and relativistic models. Observables such as its binding energy, static magnetic dipole and charge quadrupole moment, asymptotic D͞S ratio, and the elastic electromagnetic form factors place strong constraints on models for the nuclear interaction. Furthermore, the deuteron is one of the few nuclear systems for which predictions based on quantum chromodynamics have been made and tested [1][2][3][4]. The understanding of the deuteron has progressed to a level which allows the deuteron to be used as an effective neutron target in studies of the electromagnetic form factors of the neutron [5][6][7][8] and the spin structure functions of the neutron in deep inelastic scattering [9][10][11].Quasielastic scattering has been applied to determine the momentum distribution of the proton in the deuteron [12] with necessary corrections for the interaction effects [13] and to study the ͑e, e 0 p͒ reaction mechanism itself [14]: the necessity of including relativistic corrections has been demonstrated by determining the longitudinaltransverse interference structure function; details of the electromagnetic coupling to the nuclear currents have been studied by performing longitudinal-transverse separations and polarization transfer measurements, and the influence of final-state interaction (FSI) effects has been isolated by studying the fifth structure function. However, all of these measurements were performed with unpolarized deuterons. The use of polarized deuterium is advantageous, since one can select polarization observables that are sensitive to small amplitudes that are related to, for example, the charge form factor of the neutron, or the Dwave admixture in the ground-state wave function [15]. Here, we report on the first measurement of quasielastic electron scattering from polarized deuterium.It is well known that the tensor force has an important influence on deuteron structure. It introduces D-state components into the predominantly S-wave ground-state wave function and hence leads to a density distribution that depends on the spin projection m z . Because of the tensor part of the nucleon-nucleon interaction and the repulsive core at short distances, the deuteron exhibits a toroidal shape for m z 0 and a dumbbell shape for m z 61 (see, e.g., [16]). The spin-dependent momentum density distribution r m z can be written aswith R 0 ͑p͒ and R 2 ͑p͒ t...