Abstract
We have determined a value for the neutron-neutron scattering length () from high-precision measurements of time-of-flight spectra of neutrons from the capture reaction. The measurements were done at the Los Alamos Meson Physics Facility by the E1286 Collaboration. The high spatial resolution of our γ-ray detector enabled us to make a detailed assessment of the systematic uncertainties in our techniques. The value obtained in the present work is (statistical) ± 0.44 (systematic) ± 0.30 (theoretical) fm. This result is consistent with previous determinations of from the capture reaction. We found that the analysis of the data with calculations that use a relativistic phase-space factor gives a more negative value for by 0.33 fm over the analysis done using a nonrelativistic phase-space factor. Combining the present result with the previous ones from capture gives fm (theory). For the first time the combined statistical and systematic experimental uncertainty in is smaller than the theoretical uncertainty and comparable to the uncertainty in the proton-proton scattering length (). This average value of when corrected for the magnetic-moment interaction of the two neutrons becomes −18.9 ± 0.4 fm, which is 1.6 ± 0.5 fm different from the recommended value of , thereby confirming charge symmetry breaking at the 1% confidence level.
14 More- Received 13 March 2008
DOI:https://doi.org/10.1103/PhysRevC.77.054002
©2008 American Physical Society
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