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Tmore » he beta decay of tritium in the form of molecular ${\mathrm{}}_2$ is the basis of sensitive experiments to measure neutrino mass. he final-state electronic, vibrational, and rotational excitations modify the beta spectrum significantly and are obtained from theory. We further determine measurements of the branching ratios to specific ionization states for the isotopolog H. wo earlier, concordant measurements gave branching ratios of H to the bound ${\mathrm{HHe}}^{+}$ ion of 89.5% and 93.2%, in sharp disagreement with the theoretical prediction of 55%–57%, raising concerns about the theory’s reliability in neutrino mass experiments. Our finding, 56.5(6)%, is compatible with the theoretical expectation and disagrees strongly with the previous measurements.« less

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 ≤ 0.5480 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. Ourmore » data are consistent with a previous observation of an View the MathML source A₁ⁿ zero crossing near x=0.5. We find no evidence of a transition to a positive slope in (Δd+Δd¯)/(d+d¯) up to x=0.548.« less