Review of Indirect Methods Used to Determine the $^1S_0$ Neutron-Neutron Scattering Length
| dc.creator | Howell, C. R. | |
| dc.date | 2008-05-08 | |
| dc.date.accessioned | 2026-07-07T09:37:45Z | |
| dc.date.available | 2026-07-07T09:37:45Z | |
| dc.description | We have determined a value for the $^1S_0$ neutron-neutron scattering length ($a_{nn}$) from high-precision measurements of time-of-flight spectra of neutrons from the $^2H(π^-,n γ)n$ capture reaction. The measurements were done at the Los Alamos Meson Physics Facility by the E1286 collaboration. The high spatial resolution of our gamma-ray detector enabled us to make a detailed assessment of the systematic uncertainties in our techniques. The value obtained in the present work is $a_{nn} = -18$.63 $\pm $0.10 (statistical) $\pm$ 0.44 (systematic) $\pm$ 0.30 (theoretical) fm. This result is consistent with previous determinations of $a_{nn}$ from the $π^-d$ 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 $a_{nn}$ by 0.33 fm over the analysis done using a nonrelativistic phase-space factor. Combining the present result with the previous ones from $π^-d$ capture gives: $a_{nn} = - 18$.63 $\pm$ 0.27 (expt) $\pm$ 0.30 fm (theory). For the first time the combined statistical and systematic experimental uncertainty in $a_{nn}$ is smaller than the theoretical uncertainty and comparable to the uncertainty in the proton-proton $^1S_0$ scattering length ($a_{pp}$). This average value of $a_{nn}$ when corrected for the magnetic-moment interaction of the two neutrons becomes -18.9 $\pm$ 0.4 fm which is 1.6 $\pm$ 0.5 fm different from the recommended value of $a_{pp}$, thereby confirming charge symmetry breaking at the 1% confidence level. | |
| dc.description | 8 pages, 1 figure and 3 tables | |
| dc.identifier | https://arxiv.org/abs/0805.1177 | |
| dc.identifier | http://arxiv.org/abs/0805.1177 | |
| dc.identifier | Proceedings of the X International Seminar on Interactions of Neutrons with Nuclei, Dubna, Russia, ISINN-10 (2003), p. 71 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/160569 | |
| dc.subject | Nuclear Experiment | |
| dc.title | Review of Indirect Methods Used to Determine the $^1S_0$ Neutron-Neutron Scattering Length | |
| dc.type | text |