46 research outputs found
Improved Limits on Spin-Mass Interactions
Very light particles with CP-violating couplings to ordinary matter, such as
axions or axion-like particles, can mediate long-range forces between polarized
and unpolarized fermions. We describe a new experimental search for such forces
between unpolarized nucleons in two 250 kg Pb weights and polarized neutrons
and electrons in a He-K co-magnetometer located about 15 cm away. We place
improved constrains on the products of scalar and pseudoscalar coupling
constants, and (95% CL) for axion-like particle masses less than
eV, which represents an order of magnitude improvement over the best previous
neutron laboratory limit
New classes of systematic effects in gas spin co-magnetometers
Atomic co-magnetometers are widely used in precision measurements searching
for spin interactions beyond the Standard Model. We describe a new
He-Xe co-magnetometer probed by Rb atoms and use it to identify two
general classes of systematic effects in gas co-magnetometers, one associated
with diffusion in second-order magnetic field gradients and another due to
temperature gradients. We also develop a general and practical approach for
calculating spin relaxation and frequency shifts due to arbitrary magnetic
field gradients and confirm it experimentally.Comment: 5 pages, 4 figure
Observation of optical chemical shift by precision nuclear spin optical rotation measurements and calculations
Nuclear spin optical rotation (NSOR) is a recently developed technique for
detection of nuclear magnetic resonance via rotation of light polarization,
instead of the usual long-range magnetic fields. NSOR signals depend on
hyperfine interactions with virtual optical excitations, giving new information
about the nuclear chemical environment. We use a multi-pass optical cell to
perform first precision measurements of NSOR signals for a range of organic
liquids and find clear distinction between proton signals for different
compounds, in agreement with our earlier predictions. Detailed first principles
quantum-mechanical NSOR calculations are found to be in good agreement with the
measurements.Comment: 4 page
Electric Dipole Moments as Probes of CPT Invariance
Electric dipole moments (EDMs) of elementary particles and atoms probe
violations of T and P symmetries and consequently of CP if CPT is an exact
symmetry. We point out that EDMs can also serve as sensitive probes of CPT-odd,
CP-even interactions, that are not constrained by any other existing
experiments. Analyzing models with spontaneously broken Lorentz invariance, we
calculate EDMs in terms of the leading CPT-odd operators to show that
experimental sensitivity probes the scale of CPT breaking as high as
10^{12}GeV.Comment: 4 pages, typos correcte
New limits on Anomalous Spin-Spin Interactions
We report the results of a new search for long range spin-dependent
interactions using a Rb -Ne atomic comagnetometer and a rotatable
electron spin source based on a SmCo magnet with an iron flux return. By
looking for signal correlations with the orientation of the spin source we set
new constrains on the product of the pseudoscalar electron and neutron
couplings and on the product of their
axial couplings to a new particle with a
mass of less than about eV. Our measurements improve by about 2 orders
of magnitude previous constraints on such spin-dependent interactions.Comment: 4 pages, 4 figure
Nuclear-Spin Gyroscope Based on an Atomic Co-Magnetometer
An experimental nuclear-spin gyroscope is based on an alkali-metal/noblegas co-magnetometer, which automatically cancels the effects of magnetic fields. Whereas the performances of prior nuclear-spin gyroscopes are limited by sensitivity to magnetic fields, this gyroscope is insensitive to magnetic fields and to other external perturbations. In addition, relative to prior nuclear-spin gyroscopes, this one exhibits greater sensitivity to rotation. There is commercial interest in development of small, highly sensitive gyroscopes. The present experimental device could be a prototype for development of nuclear spin gyroscopes suitable for navigation. In comparison with fiber-optic gyroscopes, these gyroscopes would draw less power and would be smaller, lighter, more sensitive, and less costly
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Search for a permanent electric dipole moment using liquid 129Xe
Search for an electric dipole moment is one of the best motivated low-energy approaches for investigating physics beyond the Standard Model. Our experimental effort is focused on improving the limit on EDM in liquid 129Xe to put constraints on nuclear CP-violating interactions. High nuclear spin density and high electrical breakdown strength make 129Xe a promising medium for EDM searches. At the time the project started, the transverse nuclear spin relaxation time T2 of 129Xe was unknown. We made measurements of T2 using NMR spin-echo techniques and found that it is exceeds 1300 sec, the longest relaxation time ever measured in a liquid [1]. We also began to investigate non-linear dipolar interaction effects in a high-density spin-polarized liquid Xe. In the second iteration of the experiment we setup a high-Tc SQUID system in magnetic shields and performed detailed studies of Xe spin precession. We developed a model for non-linear dipolar interactions and found that for one set of conditions non-linear interactions can delay spin dephasing due to magnetic field gradients, while for another set of conditions they can lead to exponential amplification of the spin precession signals [2]. Our experimental data were in good quantitative agreement with predictions of the model. We also developed a series of numerical simulations to understand various imperfections in the system and made detailed experimental measurements to confirm these numerical predictions [3]. We demonstrated that non-linear interactions can amplify small precession signals and achieved an amplification factor of 10 [4]. This general phenomenon can be used in other precision measurements with non-linear interactions. We also explored practical applications of the liquid Xe system that we developed. We demonstrated that by mixing Xe with organic liquids, such as cyclopentane, one can enhance the proton spin polarization by a factor of 106 [5]. We have used this technique to perform the first measurement of the scalar J-coupling between nuclear spins in van-der-Waals molecules, something that has never been observed before. More recently, we constructed a liquid-He apparatus to acquire Xe spin precession data using a low-Tc SQUID and achieved a signal-to-noise ratio of 106. We are currently investigating factors affecting the stability of Xe spin precession signals in this system using a superconducting magnetic shield and a persistent current magnetic field coil
Laboratory Constraints on the Neutron-Spin Coupling of feV-scale Axions
Ultralight axion-like particles can contribute to the dark matter near the
Sun, leading to a distinct, stochastic signature in terrestrial experiments. We
search for such particles through their neutron-spin coupling by re-analyzing
approximately 40 days of data from a K-He co-magnetometer with a new
frequency-domain likelihood-based formalism that properly accounts for
stochastic effects over all axion coherence times relative to the experimental
time span. Assuming that axions make up all of the dark matter in the Sun's
vicinity, we find a median 95% upper limit on the neutron-spin coupling of GeV for axion masses from 0.4 to 4 feV, which is
about five orders of magnitude more stringent than previous laboratory bounds
in that mass range. Although several peaks in the experiment's magnetic power
spectrum suggest the rejection of a white-noise null hypothesis, further
analysis of their lineshapes yields no positive evidence for a dark matter
axion.Comment: 23 pages, 15 figure
Limits on isotropic Lorentz violation in QED from collider physics
We consider the possibility that Lorentz violation can generate differences
between the limiting velocities of light and charged matter. Such effects would
lead to efficient vacuum Cherenkov radiation or rapid photon decay. The absence
of such effects for 104.5 GeV electrons at the Large Electron Positron collider
and for 300 GeV photons at the Tevatron therefore constrains this type of
Lorentz breakdown. Within the context of the standard-model extension, these
ideas imply an experimental bound at the level of -5.8 x 10^{-12} <=
\tilde{\kappa}_{tr}-(4/3)c_e^{00} <= 1.2 x 10^{-11} tightening existing
laboratory measurements by 3-4 orders of magnitude. Prospects for further
improvements with terrestrial and astrophysical methods are discussed.Comment: Replaced with final version published in PR