F. Lincoln

The new LEGS highly polarized frozen-spin solid HD target facility

Three large highly H polarized frozen-spin HD targets (1.3 moles each in the solid phase) have been produced simultaneously at 20 mK and 15 Tesla with a new production facility located at Brookhaven National Laboratory. After freezing the hydrogen spins into alignment, the targets were cold transferred (at 2.5 K and 0.016 Tesla) to other cryostats with <2% loss in polarization. Highlights of the new target polarization facility are discussed.

Brute Force with a Gentle Touch: Vibration Isolation Techniques Used to Increase HD Target Polarization

The performance of statically polarized high‐field/low‐temperature targets is a strong function of the base temperature during polarization. At the Laser‐Electron Gamma Source (LEGS) facility, highly polarized Hydrogen Deuteride targets are created in a dilution refrigerator/15 tesla superconducting magnet system, and converted to a frozen spin state. This allows them to retain polarization when placed in a beam at a lower field (0.7 T) and higher temperature (1.3 K). An increase in temperature from the 0 T state to the 15 T state of the refrigerator suggested eddy currents were primarily responsible for heating of the cold finger. Vibration‐isolation techniques have been developed to reduce the level of eddy currents due to vibration inside the polarizing field. These techniques reduced the amplitude of vibration due to the pumping system by two orders of magnitude and lowered the cold finger temperature with field energized from ∼ 17 mK to ∼ 12 mK. The potential gain in polarization is substantial.

First beam-target double-polarization measurements using polarized HD at legs

A new polarized target using HD in the solid phase has been developed for studies of the nucleon spin structure at Q(2) = 0 using pion photo-production. In combination with the high quality LEGS photon beam and a large solid angle spectrometer this target allows practically background-free measurements on the proton and on the neutron. The first beam-target double-polarization data taken with this target are reported here.

Status of the legs polarized HD target

A solid, polarized HD target has been developed for the measurement of double-polarization observables in the Delta resonance region. Since the use of the first target in-beam in November 2001, dramatic improvements have been made to the in-beam and transfer cryostats and the NMR circuit has been redesigned and is well understood.

Double-Polarization Experiments using Polarized HD at LEGS

A solid, polarized HD target has been developed for the measurement of double-polarization observables in the A resonance region. The focus of the experimental program is a comparison of pion photo-production amplitudes for the neutron and proton and the associated spin-dependent sum rules.

Status of Frozen‐spin Polarized HD Targets for Spin Experiments

The first experiments have been carried out with polarized HD targets at the Laser‐Electron‐Gamma‐Source (LEGS) facility. By holding targets at low temperature and high field (17 mK and 15 Tesla) in a Dilution Refrigerator (DF) for six weeks a frozen‐spin state was reached, with equilibrium polarizations for protons and deuterons of 70% and 17%, respectively. Multiple measurements of the relaxation times and multiple transfers of the targets reduced these values so that experimental runs were carried out with polarizations of 30% and 6%, respectively. The relaxation times for protons and deuterons were observed to be 13 days and 36 days, respectively, in the beam line cryostat at 1.3 K and 0.7 Tesla magnetic field. For the future runs significantly higher D polarizations are possible by transfer of spin from the proton to the deuteron using an rf forbidden adiabatic fast passage. Higher polarizations and longer relaxation times are expected from ongoing development.

First pion photoproduction double-polarization results with polarized (H)over-right-arrow(D)over-right-arrow at LEGS

A new polarized target using HD in the solid phase has been developed for studies of the nucleon spin structure at Q(2) = 0 using pion photo-production. In combination with the high quality LEGS photon beam and a large solid angle spectrometer this target allows practically background-free measurements on the proton and on the neutron. The first beam-target double-polarization data taken with this target are reported here.

NEUTRAL PION PRODUCTION FROM DEUTERIUM AT THE LEGS FACILITY

Neutral pion photoproduction from a liquid deuterium target was measured in the energy region near 300 MeV at the LEGS facility of Brookhaven National Laboratory. The inclusive cross sections from deuterium are in agreement with measurments from Mainz, yet the exclusive cross sections and spin asymmetries for neutral pion production in coincidence with a detected nucleon are much smaller than expected from a quasi-free approximation. This may indicate that substantial final state interactions play a significant role, which will complicate the extraction of the desired amplitudes that would be measured if a free neutron target could be used.

The first pion photoproduction results from polarized HD at legs

A solid, polarized HD target has been developed for the measurement of double-polarization observables in the Delta resonance region. We report here the inaugural data obtained with this target. This new polarized target technology, combined with the high quality LEGS photon beam and the large acceptance spectrometer, SASY, provides a unique facility for studying the spin structure of the nucleon below 500 MeV. Pion production data collected on a longitudinally polarized target with six gamma-ray polarization states provides the first simultaneous measurement of d sigma/d Omega, as well as the Sigma, G and E asymmetries. With the future addition of magnetic analysis to SASY, a complete set of pion production observables on the proton and the deuteron (neutron) will be obtained.

Laser Electron Gamma Source Facility biennial progress report, June 1992

This report briefly discusses the Laser Electron Gamma Source facility and the following experiments conducted here: polarization in D(gamma, p)n and N-N tensor forces for energies less than 225 Mev; constraints on the nuclear tensor force from D(gamma, p)n for energies less than 315 Mev; the p(gamma, neutral pion) reaction and the E2 excitation of delta resonance; quasi-two- and three-body absorption in helium 3(gamma, N-N); and the delta-nucleon interaction in D(gamma,p-negative pion)p and D(gamma, p-n)neutral pions. (LSP).