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Register a new userNew limits on Anomalous Spin-Spin Interactions
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We report the results of a new search for long range spin-dependent interactions using a Rb -$^{21}$Ne atomic comagnetometer and a rotatable electron spin source based on a SmCo$_{5}$ 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 $g^e_p g^n_p/hbar c<1.7times10^{-14}$ and on the product of their axial couplings $g^e_A g^n_A/hbar c<5times10^{-42}$ to a new particle with a mass of less than about $1~mu$eV. Our measurements improve by about 2 orders of magnitude previous constraints on such spin-dependent interactions.
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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 $^3$He-K co-magnetometer located about 15 cm away. We place improved constrains on the products of scalar and pseudoscalar coupling constants, $g^n_p g^N_s < 4.2times10^{-30}$ and $g^e_p g^N_s < 1.7times10^{-30}$ (95% CL) for axion-like particle masses less than $10^{-6}$ eV, which represents an order of magnitude improvement over the best previous neutron laboratory limit.
We present measurements of the optical absorption of K vapor at 795 nm due to the presence of high pressure He gas. The results set a limit on the polarization attainable in hybrid spin-exchange optical pumping of He-3.
In the article Limits on possible new nucleon monopole-dipole interactions from the spin relaxation rate of polarized $^3$He gas, new limits on short-range, Axion-like interactions are presented. In this comment it is shown that the theoretical treatement of the data overestimates the sensitivity of the proposed method. We provide the corrected limits.
The largest hyperfine interaction coefficients in the hydrogen molecular ion HD$^+$, i.e. the electron-proton and electron-deuteron spin-spin scalar interactions, are calculated with estimated uncertainties slightly below 1~ppm. The $(Zalpha)^2 E_F$ relativistic correction, for which a detailed derivation is presented, QED corrections up to the order $alpha^3 ln^2 (alpha)$ along with an estimate of higher-order terms, and nuclear structure corrections are taken into account. Improved results are also given for the electron-proton interaction coefficient in H$_2^+$, in excellent agreement with RF spectroscopy experiments. In HD$^+$, a 4$sigma$ difference is found in the hyperfine splitting of the $(v,L)=(0,3) to (9,3)$ two-photon transition that was recently measured with high precision. The origin of this discrepancy is unknown.
The PICASSO experiment at SNOLAB reports new results for spin-dependent WIMP interactions on $^{19}$F using the superheated droplet technique. A new generation of detectors and new features which enable background discrimination via the rejection of non-particle induced events are described. First results are presented for a subset of two detectors with target masses of $^{19}$F of 65 g and 69 g respectively and a total exposure of 13.75 $pm$ 0.48 kgd. No dark matter signal was found and for WIMP masses around 24 GeV/c$^2$ new limits have been obtained on the spin-dependent cross section on $^{19}$F of $sigma_F$ = 13.9 pb (90% C.L.) which can be converted into cross section limits on protons and neutrons of $sigma_p$ = 0.16 pb and $sigma_n$ = 2.60 pb respectively (90% C.L). The obtained limits on protons restrict recent interpretations of the DAMA/LIBRA annual modulations in terms of spin-dependent interactions.
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