PNPI differential EDM spectrometer and latest results of measurements of the neutron electric dipole moment
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PNPI Differential EDM Spectrometer and Latest Results of Measurements of the Neutron Electric Dipole Moment A. P. Serebrova, *, E. A. Kolomenskiya, A. N. Pirozhkova, I. A. Krasnoshchekovaa, A. V. Vasilieva, A. O. Polyushkina, M. S. Lasakova, A. N. Murashkina, V. A. Soloveya, A. K. Fomina, I. V. Shokaa, O. M. Zherebtsova, E. B. Alexandrovb, S. P. Dmitrievb, N. A. Dovatorb, P. Geltenbortc, S. N. Ivanovc, and O. Zimmerc a
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Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, Gatchina, 188300 Russia Ioffe Physical Technical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia c Institut Max von Laue–Paul Langevin, BP 156, 38042 Grenoble Cedex 9, France *email: serebrov@pnpi. spb.ru Received February 19, 2015
Abstract—In this work, the double chamber magnetic resonance spectrometer of the Petersburg Nuclear Physics Institute (PNPI) designed to measure the neutron electric dipole moment (EDM) is briefly described. A method for long storage of polarized ultracold neutrons in a resonance space with a superposed electric field collinear to the leading magnetic field is used. The results of the measurements carried out on the ILL reactor (Grenoble, France) are interpreted as the upper limit of the value of neutron EDM |dn| < 5.5 × 10–26 e cm at the 90% confidence level. Keywords: neutron electric dipole moment, CP violation, ultracold neutrons, magnetic resonance. DOI: 10.1134/S1063778815130293
An elementary particle can have a nonzero electric dipole moment (EDM) only in the case of violation of the CP invariance of the fundamental interactions. The standard model (SM) yields estimates of the mag nitude of the neutron EDM at a level inaccessible to modern experiment. However, the SM does not explain events of the observational cosmology that provide evidence of CP violation of a much large scale in elementary processes at the earliest stages of the for mation of the Universe [1]: the visible substance in the Universe is formed by baryons—protons and neu trons—and there is practically no antimatter, the number of photons exceeding the number of baryons by about one billion times. In alternative theories [2, 3] that claim to describe the baryon asymmetry of the Universe, the neutron EDM appears to be at a level very close to the uptodate experimental limit. Observations of the neutron EDM or a new restriction on its magnitude are important criteria when selecting theoretical models that adequately describe the viola tion of CP invariance.
THE MEASUREMENT METHOD The ability of ultracold neutrons (UCNs) to be stored in material traps [4, 5] and the magnetic reso nance phenomenon [6] created in weak magnetic field Bo [7] are used. The neutron EDM is recorded by the resonance frequency shift of the neutron spin preces sion upon switching the direction of electric field E collinear to magnetic field Bo. To control the neutron polarization at the beginning and the end of the stor age period, coherent pulses of oscillating magnetic field B1
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