593 research outputs found

    Testing Electron Boost Invariance with 2S-1S Hydrogen Spectroscopy

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    There are few good direct laboratory tests of boost invariance for electrons, because the experiments required often involve repeated precision measurements performed at different times of year. However, existing measurements and remeasurements of the 2S-1S two-photon transition frequency in H--which were done to search for a time variation in the fine structure constant--also constitute a measurement of the boost symmetry violation parameter 0.83c_(TX) + 0.51c_(TY) + 0.22c_(TZ) = (4 +/- 8) x 10^(-11). This is an eight order of magnitude improvement over preexisting laboratory bounds, and with only one additional measurements, this system could yield a second comparable constraint.Comment: 8 page

    Disentangling Forms of Lorentz Violation With Complementary Clock Comparison Experiments

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    Atomic clock comparisons provide some of the most precise tests of Lorentz and CPT symmetries in the laboratory. With data from multiple such experiments using different nuclei, it is possible to constrain new regions of the parameter space for Lorentz violation. Relativistic effects in the nuclei allow us to disentangle forms of Lorentz violation which could not be separately measured in purely nonrelativistic experiments. The disentangled bounds in the neutron sectors are at the 10^(-28) GeV level, far better than could be obtained with any other current technique.Comment: 9 page

    Scaling Studies Of Spheromak Formation And Equilibrium

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    Formation and equilibrium studies have been performed on the Swarthmore Spheromak Experiment (SSX). Spheromaks are formed with a magnetized coaxial plasma gun and equilibrium is established in both small (d(small)=0.16 m) and large (d(large)=3d(small)=0.50 m) copper flux conservers. Using magnetic probe arrays it has been verified that spheromak formation is governed solely by gun physics (in particular the ratio of gun current to flux, mu(0)I(gun)/Phi(gun)) and is independent of the flux conserver dimensions. It has also been verified that equilibrium is well described by the force free condition del xB=lambda B (lambda=constant), particularly early in decay. Departures from the force-free state are due to current profile effects described by a quadratic function lambda=lambda(psi). Force-free SSX spheromaks will be merged to study magnetic reconnection in simple magnetofluid structures. (C) 1998 American Institute of Physics

    A low-noise ferrite magnetic shield

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    Ferrite materials provide magnetic shielding performance similar to commonly used high permeability metals but have lower intrinsic magnetic noise generated by thermal Johnson currents due to their high electrical resistivity. Measurements inside a ferrite shield with a spin-exchange relaxation-free atomic magnetometer reveal a noise level of 0.75 fT Hz^(-1/2), 25 times lower than what would be expected in a comparable mu-metal shield. The authors identify a 1/f component of the magnetic noise due to magnetization fluctuations and derive general relationships for the Johnson current noise and magnetization noise in cylindrical ferromagnetic shields in terms of their conductivity and complex magnetic permeability.Comment: 4 pages, 3 figures. Published in Appl. Phys. Lett.; replacement reflects published wor

    Limits on new long range nuclear spin-dependent forces set with a K-3He co-magnetometer

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    A magnetometer using spin-polarized K and 3^3He atoms occupying the same volume is used to search for anomalous nuclear spin-dependent forces generated by a separate 3^3He spin source. We measure changes in the 3^3He spin precession frequency with a resolution of 18 pHz and constrain anomalous spin forces between neutrons to be less than 2×1082 \times 10^{-8} of their magnetic or less than 2×1032\times 10^{-3} of their gravitational interactions on a length scale of 50 cm. We present new limits on neutron coupling to light pseudoscalar and vector particles, including torsion, and constraints on recently proposed models involving unparticles and spontaneous breaking of Lorentz symmetry.Comment: 4 pages, 4 figures, latest version as appeared in PR

    Dipolar and scalar 3^3He and 129^{129}Xe frequency shifts in mm-sized cells

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    We describe a 3^{3}He-129^{129}Xe comagnetometer operating in stemless anodically bonded cells with a 6 mm3^3 volume and a 129^{129}Xe spin coherence time of 300 sec. We use a 87^{87}Rb pulse-train magnetometer with co-linear pump and probe beams to study the nuclear spin frequency shifts caused by spin polarization of 3^{3}He. By systematically varying the cell geometry in a batch cell fabrication process we can separately measure the cell shape dependent and independent frequency shifts. We find that a certain aspect ratio of the cylindrical cell can cancel the effects of 3^3He magnetization that limit the stability of vapor-cell comagnetometers. Using this control we also observe for the first time a scalar 3^{3}He-129^{129}Xe collisional frequency shift characterized by an enhancement factor κHeXe=0.011±0.001\kappa_{\text{HeXe}} = -0.011\pm0.001.Comment: 4 pages, 4 figure

    Experimental Observation Of Correlated Magnetic Reconnection And Alfvénic Ion Jets

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    Correlations between magnetic reconnection and energetic ion flow events have been measured with merging force free spheromaks at the Swarthmore Spheromak Experiment. The reconnection layer is measured with a linear probe array and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The most energetic events occur in the reconnection plane immediately after formation as the spheromaks dynamically merge. The outflow velocity is nearly Alfvenic. As the spheromaks form equilibria and decay, the flow is substantially reduced
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