Status of frozen-spin polarized HD targets for spin experiments at LEGS
景谷 恒雄
Virginia Polytechnic Institute and State University / BNL 研究員
日時：2003年03月13日（木） 14:00-
場所：東北大学原子核理学研究施設３Ｆ会議室
The double spin asymmetries from circularly polarized γ beams andlongitudinally polarized HD targets have been measured at the LEGS(Laser Electron Gamma Source) facility at BNL (Brookhaven NationalLaboratory). Physics objectives are to test the GDH (Gerasimov-Drell-Hearn) sume rule and to extract the forward spin polarizabilities ofthe proton and neutron. The solid HD target has a much smaller dilutionfactor than other solid target materials and background reactions withunpolarized nucleons are significantly reduced. For these targets, HDgas is isotopically purified by distillation, doped with a small amount ofortho-H2 and frozen into a mesh of pure aluminum wires which conductsaway the heat from the ortho to para conversion of the H2 impurity.By holding the targets at low temperature and high field (17 mK and 15Tesla) in a dilution refrigerator for six weeks a frozen-spin state wasreached, with equilibrium polarizations for protons and deuterons of 70and 17 %, respectively. Multiple measurements of the relaxation timesand multiple transfers of the targets reduced these values so thatexperimental runs were carried out with polarizations of 30 and 6 %, respectively. The relaxation times for protons and deuterons wereobserved to be 13 and 36 days, respectively, in the beam line cryostatat 1.3 K and a 0.7 Tesla magnetic field. Significantly higher D polarizationsare possible by transfer of spin from the proton to the deuteron usingan rf forbidden adiabatic fast passage. These results, the present statusand future plans for HD targets will be discussed in addition to somepreliminary GDH asymmetries.