We have performed precision measurements of the double-spin virtual-photon asymmetry A1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized 3He target. Our data cover a wide kinematic range 0.277 ≤ x ≤ 0.548 at an average Q2 value of 3.078 (GeV/c)2, doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of an An1 zero crossing near x = 0.5. We ﬁnd no evidence of a transition to a positive slope in ( d + d¯)/(d + d¯) up to x = 0.548.
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We gratefully acknowledge the outstanding support of the Jefferson Lab Accelerator Division and Hall A staff in bringing this experiment to a successful conclusion. This material is based upon work supported by the U.S. Department of Energy, Ofﬁce of Science, Office of Nuclear Physics, under Award Numbers DE-FG02-87ER40315 and DE-FG02-94ER40844 and Contract DE-AC05-06OR23177, under which the Jefferson Science Associates, LLC, operate Jefferson Lab.
Allada, K.; Dutta, C.; Kolarkar, A.; Korsch, Wolfgang; Parno, D. S.; Flay, D.; Posik, M.; Armstrong, W.; Averett, T.; Benmokhtar, F.; Bertozzi, W.; Camsonne, A.; Canan, M.; and Cates, G. D., "Precision Measurements of An1 in the Deep Inelastic Regime" (2015). Physics and Astronomy Faculty Publications. 350.