Measurement of the neutron electric dipole moment via spin rotation in a non-centrosymmetric crystal

AbstractWe have measured the neutron electric dipole moment using spin rotation ina non-centrosymmetric crystal. Our result is d n = (2.5 ± 6.5 stat ± 5.5 syst ) ·10 −24 ecm. The dominating contribution to the systematic uncertainty is sta-tistical in nature and will reduce with improved statistics. The statistical sensi-tivity can be increased to 2·10 −26 ecm in 100 days data taking with an improvedsetup. We state technical requirements for a systematic uncertainty at the samelevel. Keywords: electric dipole moment, CP violation, perfect crystal, neutron,diffraction, three-dimensional polarisation analysis PACS: 14.20.Dh, 61.05.fm, 04.80.Cc1. IntroductionElectric dipole moments (EDMs) of elementary particles belong to the mostsensitive probes for CP violation beyond the Standard Model of Particle Physics[1]. Constraining or detecting EDMs of different systems allows to gather ex-perimental information about models for new physics that is complementary tohigh energy physics data.For the neutron EDM (nEDM), the most sensitive results [2, 3] were ob-tained using ultracold neutrons and Ramsey’s resonance method. See [4] fora recent review of measurements using free neutrons. Measurements using theinteractionof neutrons with the atomic electric field in absorbingmatter werepi-oneered by Shull and Nathans [5]. Abov and colleagues [6] first discussed a spin-dependent term in the scatteringamplitude for neutronsin non-centrosymmetricnon-absorptive crystals. This term is caused by the interference of nuclear and