Test of Lorentz Invariance with Spin Precession of Ultracold Neutrons

Abstract

A clock comparison experiment, analyzing the ratio of spin precession frequencies of stored ultracold neutrons and 199 Hg atoms is reported. No daily variation of this ratio could be found, from which is set an upper limit on the Lorentz invariance violating cosmic anisotropy field b ⊥ < 2 × 10 −20 eV (95% C.L.). This is the first limit for the free neutron. This result is also interpreted as a direct limit on the gravitational dipole moment of the neutron |gn| < 0.3 eV/c 2 m from a spin-dependent interaction with the Sun. Analyzing the gravitational interaction with the Earth, based on previous data, yields a more stringent limit |gn| < 3 × 10 −4 eV/c 2 m.PACS numbers: 14.20. Dh, 11.30.Er, 11.30.Cp, Lorentz symmetry is a fundamental hypothesis of our current understanding of physics and is central to the foundations of the Standard Model of particle physics (SM). However, the SM is widely believed to be only the low energy limit of some more fundamental theory, a theory which will probably violate more symmetries than the SM, in order to accomodate some features of the universe currently lacking in the SM, e.g., the baryon asymmetry. A SM extension including Lorentz and CPT violating terms has been presented in [1]. It provides a parametrisation of effects suitable to be tested by low energy precision experiments. In particular, clock comparison experiments [2, 3] have proven to be particularly sensitive to spin-dependent effects arising from a so-called cosmic spin anisotropy fieldb filling the whole universe. This Letter reports on a search for such an exotic field via its coupling to free neutrons.In the presence of a fieldb, the two spin states of the neutron will encounter an extra contribution to the energy splitting corresponding to the potential V = σ ·b where σ are the Pauli matrices. Thus, if a neutron is subjected to both a static magnetic field B and the new field b, its spin will precess at the modified Larmor frequency f n , which to first order inb is given byWe searched for a sidereal modulation (at a period of 23.934 hours) of the neutron Larmor frequency induced by b ⊥ , the component ofb orthogonal to the Earth's rotation axis. The experiment is also sensitive to a possible influence of the Sun on the spin precession dynamics, leading to a solar modulation (at a period of 24 h) of the Larmor frequency, as proposed in [4]. Such an effect could arise from a non-standard spin-dependent component of gravity [5,6] or from another long-range spindependent force [7,8]. In particular, a non-zero neutron gravitational dipole moment g n would induce a coupling through (see also [9])where G is Newton's constant, and for the mass M and

Comparison of ultracold neutron sources for fundamental physics measurements

“…The emergent discussion for dark matter and dark energy triggered further use of UCNs to search for exotic physics beyond the Standard Model of particle physics, like searches for mirror matter [34][35][36], for Lorentz violation effects [37], for exotic interactions induced by axionlike particles [38][39][40][41][42], dark matter [43,44], or probing dark energy [45][46][47]. The sensitivities of all such UCN experiments depend directly on the total UCN statistics available in the measurement, hence on high UCN densities in sizeable storage vessels.…”

Tests ofCPTand Lorentz symmetry from muon anomalous magnetic dipole moment

“…between a background cosmic field, b, and the spin of an electron, proton, neutron and muon, σ, and constraints on the strengths of such interactions have been obtained [1][2][3][4][5][6][7][8][9][10][11]. For further details on the broad range of experiments performed in this field and a brief history of the improvements in these limits, we refer the reader to the reviews of [12,13] and the references therein.…”

Laser frequency combs and ultracold neutrons to probe braneworlds through induced matter swapping between branes

“…In the present work, we investigate further this effect by reconsidering it from a more realistic experimental point of view. To that end, a simple and inexpensive experimental setup is proposed, inspired from designs used in neutron physics investigations [10][11][12][13] and in spectroscopy [14][15][16][17].…”