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Register a new userImproved Limits on Long-Range Parity-Odd Interactions of the Neutron
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We show that a previous polarized 3He experiment at Princeton, plus Eot-Wash equivalence-principle tests, constrain exotic, long-ranged (lambda > 0.15m) parity-violating interactions of neutrons at levels well below those inferred from a recent study of the parity-violating spin-precession of neutrons transmitted through liquid 4He. For lambda > 1.0e8 meters the bounds on gAgV are improved by a 11 orders of magnitude.
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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.
Couplings between standard model particles and unparticles from a nontrivial scale invariant sector can lead to long range forces. If the forces couple to quantities such as baryon or lepton (electron) number, stringent limits result from tests of the gravitational inverse square law. These limits are much stronger than from collider phenomenology and astrophysics.
A search for millicharged particles, a simple extension of the standard model, has been performed with the ArgoNeuT detector exposed to the Neutrinos at the Main Injector beam at Fermilab. The ArgoNeuT Liquid Argon Time Projection Chamber detector enables a search for millicharged particles through the detection of visible electron recoils. We search for an event signature with two soft hits (MeV-scale energy depositions) aligned with the upstream target. For an exposure of the detector of $1.0$ $times$ $10^{20}$ protons on target, one candidate event has been observed, compatible with the expected background. This search is sensitive to millicharged particles with charges between $10^{-3}e$ and $10^{-1}e$ and with masses in the range from $0.1$ GeV to $3$ GeV. This measurement provides leading constraints on millicharged particles in this large unexplored parameter space region.
Present probes do not exclude that the neutron ($n$) oscillation into mirror neutron ($n$), a sterile state exactly degenerate in mass with the neutron, can be a very fast process, in fact faster than the neutron decay itself. This process is sensitive to the magnetic field. Namely, if the mirror magnetic field $vec{B}$ exists at the Earth, $n-n$ oscillation probability can be suppressed or resonantly amplified by the applied magnetic field $vec{B}$, depending on its strength and on the angle $beta$ between $vec{B}$ and $vec{B}$. We present the results of ultra-cold neutron storage measurements aiming to check the anomalies observed in previous experiments which could be a signal for $n-n$ oscillation in the presence of mirror magnetic field $Bsim 0.1$~G. Analyzing the experimental data on neutron loses, we obtain a new lower limit on $n-n$ oscillation time $tau_{nn} > 17$ s (95 % C.L.) for any $B$ between 0.08 and 0.17 G, and $tau_{nn}/sqrt{cosbeta} > 27 $s (95 % C.L.) for any $B$ in the interval ($0.06div0.25$) G.
We present a search for possible spin dependent interactions of the neutron with matter through exchange of spin 1 bosons with axial vector couplings as envisioned in possible extensions of the Standard Model. This was sought using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that this interaction would tilt the plane of polarization and develop a component along the neutron momentum. The result for the rotation angle, $phi_{V_5} = [2.8pm,4.6(stat.)pm,4.0(sys.)]times 10^{-5}~mbox{rad/m}$ is consistent with zero. This result improves the upper bounds on the neutron-matter coupling $g_{A}^{2}$ from such an interaction by about three orders of magnitude for force ranges in the mm-$mu$m regime.
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