Physics Letters B (May 2015)

Constraining interactions mediated by axion-like particles with ultracold neutrons

  • S. Afach,
  • G. Ban,
  • G. Bison,
  • K. Bodek,
  • M. Burghoff,
  • M. Daum,
  • M. Fertl,
  • B. Franke,
  • Z.D. Grujić,
  • V. Hélaine,
  • M. Kasprzak,
  • Y. Kermaïdic,
  • K. Kirch,
  • P. Knowles,
  • H.-C. Koch,
  • S. Komposch,
  • A. Kozela,
  • J. Krempel,
  • B. Lauss,
  • T. Lefort,
  • Y. Lemière,
  • A. Mtchedlishvili,
  • O. Naviliat-Cuncic,
  • F.M. Piegsa,
  • G. Pignol,
  • P.N. Prashanth,
  • G. Quéméner,
  • D. Rebreyend,
  • D. Ries,
  • S. Roccia,
  • P. Schmidt-Wellenburg,
  • A. Schnabel,
  • N. Severijns,
  • J. Voigt,
  • A. Weis,
  • G. Wyszynski,
  • J. Zejma,
  • J. Zenner,
  • G. Zsigmond

Journal volume & issue
Vol. 745
pp. 58 – 63

Abstract

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We report a new limit on a possible short range spin-dependent interaction from the precise measurement of the ratio of Larmor precession frequencies of stored ultracold neutrons and Hg199 atoms confined in the same volume. The measurement was performed in a ∼1μT vertical magnetic holding field with the apparatus searching for a permanent electric dipole moment of the neutron at the Paul Scherrer Institute. A possible coupling between freely precessing polarized neutron spins and unpolarized nucleons of the wall material can be investigated by searching for a tiny change of the precession frequencies of neutron and mercury spins. Such a frequency change can be interpreted as a consequence of a short range spin-dependent interaction that could possibly be mediated by axions or axion-like particles. The interaction strength is proportional to the CP violating product of scalar and pseudoscalar coupling constants gSgP. Our result confirms limits from complementary experiments with spin-polarized nuclei in a model-independent way. Limits from other neutron experiments are improved by up to two orders of magnitude in the interaction range of 10−6<λ<10−4m. Keywords: CP violation, Short range spin-dependent interaction, Axion, Axion-like particle, Ultracold neutrons, Neutron electric dipole moment