Constraints on Spin-Dependent Short-Range Interaction between Nucleons

Abstract

We search for a spin-dependent P -and T -violating nucleon-nucleon interaction mediated by light pseudoscalar bosons such as axions or axion-like particles. We employed an ultra-sensitive low-field magnetometer based on the detection of free precession of co-located 3 He and 129 Xe nuclear spins using SQUIDs as low-noise magnetic flux detectors. The precession frequency shift in the presence of an unpolarized mass was measured to determine the coupling of pseudoscalar particles to the spin of the bound neutron. For boson masses between 2 µeV and 500 µeV (force ranges between 3·10 −4 m -10 −1 m) we improved the laboratory upper bounds by up to 4 orders of magnitude. origin into a photon in the presence of a static magnetic field. However, any axion or axion-like particle that couples with both scalar and pseudoscalar vertices to fundamental fermions would also mediate a parity and time-reversal symmetryviolating force between a fermion f and the spin of another fermion f σ , which is parameterized by a Yukawatype potential with range λ and a monopole-dipole coupling given by [8]:σ is the spin vector and λ is the range of the Yukawa-force with λ= /(m a c). Thus, the entire axion window can be probed by searching for spin-dependent short-range forces in the range between 20 µm and 0.2 m. g f s and g fσ p are dimensionless scalar and pseudoscalar coupling constants which in our case correspond to the scalar coupling of an axion-like particle to a nucleon (g . Accordingly, we have m fσ = m n .r is the unit distance vector from the bound neutron to the nucleon. The potential given by Eq. 1 effectively acts near the surface of a massive unpolarized sample as a pseudomagnetic field and gives rise to a shift ∆ν sp = 2 · V Σ /h, e.g., in the precession frequency of nuclear spin-polarized gases ( 3 He and 129 Xe), which according to the Schmidt model [9] can be regarded as an effective probe of spinpolarized bound neutrons. The potential V Σ is obtained by integration of V sp (r) from Eq. 1 over the volume of the massive unpolarized sample averaged over the volume of the polarized spin-sample, each having a cylindrical shape. Based on the analytical derivation of V Σ,∞ for disc-shaped spin-and matter samples with respective thicknesses D and d [10], we obtainη(λ) takes account for the finite size in transverse direction of our cylindrical samples and ∆x represents the finite gap between them. Furthermore, κ = 2 g N s g n p /(8π · m n ) and N is the nucleon number density of the unpolarized matter sample. η(λ) 1 is determined numerically for our cylindrically shaped spin-and matter samples at "close"-position (see Fig. 1). Our experimental approach to search for non-magnetic, spin-dependent interactions is to use an ultra-sensitive low-field comagnetometer based on detection of free spin precession of gaseous, nuclear polarized samples [11]. The Larmor frequencies of 3 He and 129 Xe in a guiding magnetic field B are given by ω L,He(Xe) = γ He(Xe) · B, with γ He(Xe) being the gyromagnetic ratios of the respective gas species...

Nuclear Matrix Elements for Tests of Local Lorentz Invariance Violation

“…Such tests include searches for violation of local Lorentz and CPT symmetry [1], [2], [3], [4], and for new spin-dependent forces mediated by light particles, such as an axion [5], [6], [7], [8], [9], [10].…”

Search for exotic spin-dependent interactions with a spin-exchange relaxation-free magnetometer

“…The setup of the test mass described in this paper can be also applied to other systems with different test masses to test spin-dependent and velocity-dependent interactions: for example, polarized atoms [26][27][28][29] for polarized nucleons, paramagnetic insulator [42] for polarized electrons.…”

“…For an unpolarized test mass, we assume to use a nonmagnetic bismuth germanate insulator (Bi 4 Ge 3 O 12 , or BGO) with the high nucleon density (7.13 g/cm 3 = 4.3 × 10 24 nucleons/cm 3 ) which has been previously used [29]. In this paper, we only theoretically calculated the spin-dependent interactions between the polarized electrons in the vapor cell and the unpolarized nucleons in the BGO test mass.…”

“…The detection of spin-dependent interactions, therefore, will enable to distinguish the axion from the scalar boson [15]. The static spin-dependent interactions have been carefully investigated for polarized electrons: experiments with a torsion pendulum [16][17][18][19][20][21] and paramagnetic salt [22][23][24] and for nucleons: measurements of precession frequency of atomic gases [25][26][27][28][29]; experiments with an ion trap [30] and neutron bound states [31,32]; spinrelaxation measurements of polarized particles [33][34][35][36]. On the other hand, the experimental constraints on the interactions dependent on both spins and the relative velocity are very few.…”

Neutrons Knock at the Cosmic Door

“…Axion interactions in the so-called "axion window," given by the Yukawa length 0.2 μm < λ < 2 cm (corresponding to axion masses 10 −5 eV ≤ m a ≤ 1 eV), are still allowed by otherwise stringent constraints [8]. Recent reviews [9] and [10] cover this topic. The most restrictive limit on this product g s g p has been derived by combining the existing laboratory limit on the scalar coupling g s with stellar energy-loss limits on the pseudoscalar coupling g p [11].…”