Precision measurements of free-neutron β decay have been used to precisely constrain our understanding of the weak interaction. However, the neutron Fierz interference term bn, which is particularly sensitive to beyond-standard-model tensor currents at the TeV scale, has thus far eluded measurement. Here we report the first direct constraints on this term, finding bn = 0.067 ± 0.005stat+0.090-0.061sys, consistent with the standard model. The uncertainty is dominated by absolute energy reconstruction and the linearity of the β spectrometer energy response.
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This work is supported in part by the US Department of Energy, Office of Nuclear Physics (DE-FG02-08ER41557, DE-SC0014622, DE-FG02-97ER41042) and the National Science Foundation (Grants No. NSF-0653222, No. NSF-0700491, No. NSF-0855538, No. NSF-1002814, No. NSF-1005233, No. NSF-1205977, No. NSF-1306997, No. NSF-1307426, No. 1506459, and No. NSF-1615153).
Hickerson, K. P.; Sun, X.; Bagdasarova, Y.; Bravo-Berguño, D.; Broussard, L. J.; Brown, M. A. -P.; Carr, R.; Currie, S.; Ding, X.; Filippone, B. W.; García, A.; Geltenbort, P.; Hoagland, J.; Holley, A. T.; Hong, R.; Ito, T. M.; Knecht, A.; Liu, C. -Y.; Liu, J. L.; Makela, M.; Mammei, R. R.; Martin, J. W.; Melconian, D.; Mendenhall, M. P.; Moore, S. D.; Morris, C. L.; Pattie, R. W. Jr.; Pérez Galván, A.; Picker, R.; Pitt, M. L.; and Plaster, Bradley R., "First Direct Constraints on Fierz Interference in Free-Neutron β Decay" (2017). Physics and Astronomy Faculty Publications. 537.