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Time reversal and the neutron |
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| Authors: | T E Chupp R L Cooper K P Coulter S J Freedman B K Fujikawa G L Jones A Garcia H P Mumm J S Nico A K Thompson C Trull F E Wietfeldt J F Wilkerson |
| Institution: | 1. Univeristy of Michigan, Ann Arbor, MI, 48109, USA 2. University of California and Lawrence Berkeley Laboratory, Berkeley, CA, 94720, USA 3. Hamilton College, Hamilton, NY, 13323, USA 4. University of Washington, Seattle, WA, 98195, USA 5. National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA 6. Tulane University, New Orleans, LA, 70118, USA 7. University of North Carolina, Chapel Hill, NC, 27599, USA 8. Oak Ridge National Lab, Oak Ridge, TN, 37831, USA |
| Abstract: | We have measured the triple correlation $D\langle\vec J_n\rangle/J_n\cdot (\vec\beta_e\times\hat p_\nu)$ with a polarized cold-neutron beam (Mumm et al., Phys Rev Lett 107:102301, 2011; Chupp et al., Phys Rev C 86:035505, 2012). A non-zero value of D can arise due to parity-even-time-reversal-odd interactions that imply CP violation. Final-state effects also contribute to D at the level of 10???5 and can be calculated with precision of 1 % or better. The D coefficient is uniquely sensitive to the imaginary part of the ratio of axial-vector and vector beta-decay amplitudes as well as to scalar and tensor interactions that could arise due to beyond-Standard-Model physics. Over 300 million proton-electron coincidence events were used in a blind analysis with the result D?=????0.94±1.89 (stat)±0.97(sys)]×10???4. Assuming only vector and axial vector interactions in beta decay, our result can be interpreted as a measure of the phase of the axial-vector coupling relative to the vector coupling, $\phi_{\rm AV}= 180.012^\circ \pm 0.028^\circ$ . This result also improves constrains on certain non-VA interactions. |
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