A Search for Neutron to Mirror-Neutron Oscillations

Lee and Yang had noted, in their Nobel prize winning paper, that observation of apparent parity violation in the weak interaction of particles could be mitigated with the introduction of a parity conjugated copy of the same particles. The existence of a parity conjugated copy in terms of the weak interaction of normal matter, called mirror matter, that does not interact with normal matter through known forces, has long been theorized. Baryon number violation is required for baryogenesis in order to explain the observed asymmetry between matter and antimatter in the universe. Neutron to mirror-neutron oscillations could be an observable baryon number violating process. In late 2000s, it was pointed out that the oscillation time of such neutron to mirror-neutron oscillation could be of the order of a few seconds, and that a magnetic field dependent ultracold neutron storage measurement could be sensitive to such oscillations. Furthermore, it was also shown that the ambient mirror magnetic field on the surface of the Earth could be as high as the Earth's magnetic field. Subsequently, two separate groups performed experiments at the Institut Laue-Langevin in search of neutron to mirror-neutron oscillations and reported having found no evidence. The limit set on the oscillation time was $\tau_{nn'} > 414~$s (90\% C.L.) for the case where the mirror magnetic field, $B'=0$, and $\tau_{nn'}>12~$s (95\% C.L.) for the case where $B'\in(0,12.5)~\mu$T. These constraints have since been improved to $\tau_{nn'} > 448~$s (90\% C.L., $B'=0$), $\tau_{nn'} > 17~\text{s}~\forall~B'\in(8,17)~\mu\text{T (95\% C.L.)}$, and $\tau_{nn'} > 27~\text{s}~\forall~B'\in(6,25)~\mu\text{T (95\% C.L.)}$. Soon after, when the results of these experiments were further analyzed by Berezhiani et al., $5\sigma$, $3\sigma$, and $2.5\sigma$ statistically significant signals for mirror-neutron oscillation in the presence of a non zero mirror magnetic field were reported. The current leading constraints upon $\tau_{nn'}$ do not exclude these signals. Thus a new experiment was required to test these claimed signals. The neutron electric dipole moment experiment based at the Paul Scherrer Institute performed a dedicated search to investigate these signals and found no evidence of neutron mirror-neutron oscillations. We thereby impose the following new lower limits on the oscillation time: $\tau_{nn'} > 388~$s (90\% C.L., $B'=0$), $\tau_{nn'} > 6~\text{s}~\forall~B'\in(0.38,25.66)~\mu\text{T (95\% C.L.)}$, and $\left(\tau_{nn'}/\sqrt{\cos(\beta)}\right) > 9~\text{s}~\forall~B'\in(5.04,25.39)~\mu\text{T (95\% C.L.)}$, where $\beta$ is the fixed angle between the applied magnetic field and the ambient mirror magnetic field, which is bound to the reference frame of the Earth. For the case when the mirror magnetic field is fixed in the cosmos, we have also for the first time placed the following constraints: $\tau^{\Omega_{\bigoplus}}_{nn'} > 7~\text{s (95\% C.L.)}~\forall~B'\in(5.20,24.43)~\mu\text{T}$, $\tau^{\Omega_{2\bigoplus}}_{nn'}~>~6~\text{s}~\forall~B'\in(5.51,25.78)~\mu\text{T}~(95\%~\text{C.L.})$, $\tau^{\Omega_{\bigodot}}_{nn'}~>~4~\text{s}~\forall~B'\in(6.77,27.18)~\mu\text{T}~(95\%~\text{C.L.})$, and $\tau^{\Omega_{2\bigodot}}_{nn'}~>~5~\text{s}~\forall~B'\in(4.20,24.17)~\mu\text{T}~(95\%~\text{C.L.})$, for modulation frequencies associated with one sidereal day, half a sidereal day, an annual year, and half an annual year, respectively. Our new constraints in the assumption of a mirror magnetic field bound to Earth are the best constraints around $B'\sim10~\mu$T, and also in the region where the mirror magnet field falls in the range of $B'>37~\mu$T. While this result excludes large portions of the three statistically significant signals indicated by Berezhiani et al., especially where at least two signal regions overlap, it does not exclude all the signals. We therefore need further tests of these signals in the vicinity of $B'\in(4,37)~\mu$T

Search for ultralight axion dark matter in a side-band analysis of a ¹⁹⁹Hg free-spin precession signal

Ultra-low-mass axions are a viable dark matter candidate and may form a coherently oscillating classical field. Nuclear spins in experiments on Earth might couple to this oscillating axion dark-matter field, when propagating on Earth's trajectory through our Galaxy. This spin coupling resembles an oscillating pseudo-magnetic field which modulates the spin precession of nuclear spins. Here we report on the null result of a demonstration experiment searching for a frequency modulation of the free spin-precession signal of \magHg in a 1μT magnetic field. Our search covers the axion mass range 10⁻¹⁶ eV ≲ m_a ≲ 10⁻¹³ eV and achieves a peak sensitivity to the axion-nucleon coupling of g_aNN ≈ 3.5 × 10⁻⁶ GeV⁻¹.ISSN:2542-465

Search for an interaction mediated by axion-like particles with ultracold neutrons at the PSI

We report on a search for a new, short-range, spin-dependent interaction using a modified version of the experimental apparatus used to measure the permanent neutron electric dipole moment at the Paul Scherrer Institute. This interaction, which could be mediated by axion-like particles, concerned the unpolarized nucleons (protons and neutrons) near the material surfaces of the apparatus and polarized ultracold neutrons stored in vacuum. The dominant systematic uncertainty resulting from magnetic-field gradients was controlled to an unprecedented level of approximately 4 pT cm⁻¹ using an array of optically-pumped cesium vapor magnetometers and magnetic-field maps independently recorded using a dedicated measurement device. No signature of a theoretically predicted new interaction was found, and we set a new limit on the product of the scalar and the pseudoscalar couplings gₛgₚλ² < 8.3 × 10⁻²⁸ m² (95% C.L.) in a range of 5 µm < λ < 25 mm for the monopole–dipole interaction. This new result confirms and improves our previous limit by a factor of 2.7 and provides the current tightest limit obtained with free neutrons.ISSN:1367-263

Mapping of the magnetic field to correct systematic effects in a neutron electric dipole moment experiment

Experiments dedicated to the measurement of the electric dipole moment of the neutron require outstanding control of the magnetic-field uniformity. The neutron electric dipole moment (nEDM) experiment at the Paul Scherrer Institute uses a Hg199 co-magnetometer to precisely monitor temporal magnetic-field variations. This co-magnetometer, in the presence of field nonuniformity, is, however, responsible for the largest systematic effect of this measurement. To evaluate and correct that effect, offline measurements of the field nonuniformity were performed during mapping campaigns in 2013, 2014, and 2017. We present the results of these campaigns, and the improvement the correction of this effect brings to the neutron electric dipole moment measurement.ISSN:1094-1622ISSN:0556-2791ISSN:1050-294

Erratum to: Data blinding for the nEDM experiment at PSI

ISSN:1434-6001ISSN:1434-601

Determining the neutrino mass with cyclotron radiation emission spectroscopy—Project 8

The most sensitive direct method to establish the absolute neutrino mass is observation of the endpoint of the tritium beta-decay spectrum. Cyclotron radiation emission spectroscopy (CRES) is a precision spectrographic technique that can probe much of the unexplored neutrino mass range with O(eV) resolution. A lower bound of m(νe) ≳ 9(0.1) meV is set by observations of neutrino oscillations, while the KATRIN experiment-the current-generation tritium beta-decay experiment that is based on magnetic adiabatic collimation with an electrostatic (MAC-E) filter-will achieve a sensitivity of m(νe) ≲ 0.2 eV. The CRES technique aims to avoid the difficulties in scaling up a MAC-E filter-based experiment to achieve a lower mass sensitivity. In this paper we review the current status of the CRES technique and describe Project 8, a phased absolute neutrino mass experiment that has the potential to reach sensitivities down to m(νe) ≲ 40 meV using an atomic tritium source.United States. Department of Energy (Grant DE-SC0011091