Measurement of Tensor Analyzing Powers for Elastic Electron Scattering from a Polarized2H Target Internal to a Storage Ring

Abstract

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

Electromagnetic structure of few-nucleon ground states

“…[38,34,30,43,46,40,47,35,29,28], and for T 20 (Q) to Refs. [51,52,49,53,54,59,55,56,57,60,58]. Note that Refs.…”

Elastic electron scattering from light nuclei

“…With this setup it became possible to reach the region of the zero crossing of the C0 form factor at 4.4f m −1 . Further measurements using an internal tensor-polarized gas target were carried out at the AMPS storage ring [130,131]. The deuterons were produced using an atomic-beam source which injected the deuterons into a storage cell traversed by the electron beam.…”

Precise Measurement of Deuteron Tensor Analyzing Powers with BLAST

“…During the last two decades, measurements of tensor-polarized observables, made possible by innovative accelerator and target technologies, have provided new experimental information to understand the electromagnetic structure of the deuteron [4][5][6][7][8][9][10][11][12] and put strong constraints on nuclear models, e.g., Hamiltonian dynamics [13,14], explicitly covariant models [15,16], as well as the latest developments in effective field theory for low-Q physics [17,18]. In this Letter, a highprecision measurement of the deuteron tensor analyzing powers T 20 and T 21 over a broad range of low-momentum transfer is reported.…”

“…Tensor-polarized observables can be measured as tensor moments of recoiling deuterons with unpolarized beam and target [4,8,11] or as tensor asymmetries with a tensor-polarized target [5][6][7]9,10,12]. The experiment reported in this Letter used a highly polarized deuterium gas target with a large acceptance magnetic spectrometer, which is different from all previous experiments.…”

“…Results for T 20 and T 21 [grey (red online) dots] compared to previous data [4] (open dots), [5,6] (open upright triangles), [7] (solid upright triangles), [8] (solid dots), [9] (open squares), [10] (solid squares), [11] (open stars), [12] (solid down triangles), and various theoretical predictions. The theoretical curves are nonrelativistic models with relativistic corrections [13] (long dashed line), [14] (dashed line), relativistic models [15] (dash-dotted line), [16] (dotted line), and effective field theory [17,18] (grey error band).…”