2015: Constraining interactions mediated by axion-like particles with ultracold neutrons

Phys. Lett. B 745, 58-63 (2015)

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




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 199Hg 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.