1. The 3He(\vec n,p)3H parity-conserving asymmetry
- Author
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Viviani, M., Baeßler, S., Barrón-Palos, L., Birge, N., Bowman, J. D., Calarco, J., Cianciolo, V., Coppola, C. E., Crawford, C. B., Dodson, G., Fomin, N., Garishvili, I., Gericke, M. T., Girlanda, L., Greene, G. L., Hale, G. M., Hamblen, J., Hayes, C., Iverson, E. B., Kabir, M. L., Kievsky, A., Marcucci, L. E., McCrea, M., Plemons, E., Ramírez-Morales, A., Mueller, P. E., Novikov, I., Penttila, S. I., Scott, E. M., Watts, J., and Wickersham, C.
- Subjects
Nuclear Experiment ,Nuclear Theory - Abstract
Recently, the n$^3$He collaboration reported a measurement of the parity-violating (PV) proton directional asymmetry $A_{\mathrm {PV}} = (1.55\pm 0.97~\mathrm {(st\ at)} \pm 0.24~\mathrm {(sys)})\times 10^{-8}$ in the capture reaction of ${}^3$He$(\vec {n},{\mathrm p}){}^3$H at meV incident neutron energies. The result increased the limited inventory of precisely measured and calculable PV observables in few-body systems required to further understand the structure of hadronic weak interaction. In this letter, we report the experimental and theoretical investigation of a parity conserving (PC) asymmetry $A_{\mathrm {PC}}$ in the same reaction (the first ever measured PC observable at meV neutron energies). As a result of S- and P-wave mixing in the reaction, the $A_{\mathrm {PC}}$ is inversely proportional to the neutron wavelength $\lambda$. The experimental value is $(\lambda\times A_{\mathrm {PC}})\equiv\beta= (-1.97 \pm 0.28~\mathrm{(stat)}\pm 0.12~\mathrm{(sys)}) \times 10^{-6}$ Amstrongs. We present results for a theoretical analysis of this reaction by solving the four-body scattering problem within the hyperspherical harmonic method. We find that in the ${}^3$He$(\vec {n},{\mathrm p}){}^3$H reaction, $A_{\mathrm {PC}}$ depends critically on the energy and width of the close $0^-$ resonant state of ${}^4$He, resulting in a large sensitivity to the spin-orbit components of the nucleon-nucleon force and even to the three-nucleon force. The analysis of the accurately measured $A_{\mathrm {PC}}$ and $A_{\mathrm {PV}}$ using the same few-body theoretical models gives essential information needed to interpret the PV asymmetry in the ${}^3$He$(\vec {n}, {\mathrm p}){}^3$H reaction., Comment: 8 pages, 3 figures
- Published
- 2024