Constraint on the coupling of axionlike particles to matter via an ultracold neutron gravitational experiment

Abstract

We present a new constraint for the axion monopole-dipole coupling in the range of 1 µm -a few mm, previously unavailable for experimental study. The constraint was obtained using our recent results on the observation of neutron quantum states in the Earth's gravitational field. We exploit the ultimate sensitivity of ultra-cold neutrons (UCN) in the lowest gravitational states above a material surface to any additional interaction between the UCN and the matter, if the characteristic interaction range is within the mentioned domain. In particular, we find that the upper limit for the axion monopole-dipole coupling constant is gpgs/( c) < 2 10 −15 for the axion mass in the "promising" axion mass region MA ∼ 1 meV.A vanishing value for the neutron electric dipole moment motivated the introduction of hypothetical light (pseudo) scalar bosons (commonly called axions), as an extension of the Standard Model [1,2,3,4]. According to the suggested theories the axion mass could be in the range of 10 −6 < M A < 10 −1 eV, while its coupling to photons, leptons and nucleons is not fixed by the existing models (though it is extremely weak). Following the theoretical predictions mentioned intensive searches for axions have been performed over recent decades. These studies include testing the astrophysical consequences of the axion theories, QED effects (axion-two photon coupling) and macroscopic forces (spin-matter coupling). They put severe constraints on axion-matter coupling in different axion mass ranges. A detailed review of axion studies can be found in [5,6].The recently reported positive results of the PVLAS experiment on light polarization rotation in a vacuum in the presence of a transverse magnetic field [7] may be seen as evidence of the long sought axion [8]. According to [7], the mass of neutral boson possibly responsible for the observed signal is 1 < M A < 1.5 meV.The value of the axion-photon coupling strength obtained from the PVLAS experiment is in contradiction with recent CAST observations [9]. Several ideas have been discussed recently, in [10,11], capable of explaining this discrepancy.This intriguing result makes it particularly important to carry out independent testing on the axion-matter coupling in the corresponding distance range of 130 < λ < 200 µm.In the present Letter we report on constraints for axion monopole-dipole coupling. Such coupling results in a spin-matter CP violating Yukawa-type interaction potential [12]between spin and matter, where g p g s is the product of couplings at the scalar and polarized vertices and λ is the force range. Here r is the distance between a neutron and a nucleus, n = r/r is a unitary vector, and m is the nucleon mass. Only a few experiments for distances below 100 mm have placed upper limits on the product coupling in a system of magnetized media and test masses [6]. One experiment [13] had peak sensitivity at ∼ 100 mm and two other ones [14,15] had peak sensitivity at ∼ 10 mm.The constraint for the g s g p presented in this article is competitive in the dista...

Experimental limits on neutron disappearance into another braneworld

“…In the mirror world approaches, the matter-mirror matter mixing is also considered (with neutron and mirror neutron [11] for instance) though, in the best of our knowledge, a full derivation through a brane formalism is still lacking. Actually, ultracold neutron (UCN) experiments related to the neutron disappearance are then fundamental since they could allow to quantify or to distinguish among the different predicted phenomenologies [21,22].…”

Neutrons Knock at the Cosmic Door

“…This corresponds to the most stringent upper limit from a direct search for attractive and repulsive g s g p coupling. This limit is a factor of 30 more precise than the one derived [29] from our previous experiment with UCN [13,14].…”

“…Our limit for a repulsive (attractive) coupling is shown in a solid (dashed) line marked with A þ ðA−Þ. The limits are a factor of 30 more precise than the previous ones derived from a direct measurement at the micron length scale [29] derived from our previous experiment with UCN marked B [13,14]. PRL 112, 151105 (2014) P H Y S I C A L R E V I E W L E T T E R S week ending 18 APRIL 2014 151105-4 attractive coupling strength g s g p > 3 × 10 −16 is excluded.…”

Limits on possible new nucleon monopole-dipole interactions from the spin relaxation rate of polarizedHe3gas

“…This work also summarized the existing experimental constraints known at that time for some of the interactions. Most of the experiments which have been performed to search for such interactions [9,[11][12][13][14][15][16][17] are sensitive to ranges λ > 1 cm.…”

“…Baeßler et al [12] used the observation of neutron bound states in the Earth's gravitational potential and the apparent absence of a spin-dependence for the bound state energies to place an upper bound on g s g p for length scales of order micrometers, which is the characteristic spatial separation of the bound state wave function from the surface. A spatially inhomogeneous monopole-dipole interaction σ · r (Eq.…”