Many particle-physics models that extend the standard model predict the existence of long-range spin-spin interactions. We propose an approach that uses the Earth as a polarized spin source to investigate these interactions. Using recent deep-Earth geophysics and geochemistry results, we create a comprehensive map of electron polarization within the Earth induced by the geomagnetic field. We examine possible long-range interactions between these spin-polarized geoelectrons and the spin-polarized electrons and nucleons in three laboratory experiments. By combining our model and the results from these experiments, we establish bounds on torsion gravity and possible long-range spin-spin forces associated with the virtual exchange of either spin-one axial bosons or unparticles.

We use the recently developed model of the electron spins within the Earth to investigate all of the six possible long-range velocity-dependent spin-spin interactions associated with the exchange of an intermediate vector boson. Several laboratory experiments have established upper limits on the energy associated with various fermion-spin orientations relative to the Earth. We combine the results from three of these experiments with the geoelectron-spin model to obtain bounds on the velocity-dependent interactions that couple electron spin to the spins of electrons, neutrons and protons. Five of the six possible potentials investigated were previously unbounded. The bound achieved on V 8 is about 30 orders of magnitude more restrictive in the long-range limit than the only previously established constraint.Recently, there has been renewed interest in exploring possible anomalous spin-spin interactions mediated by new particles [1][2][3][4][5][6][7]. Observation of such an interaction would constitute the discovery of a new force in nature and suggest physics beyond the standard model of particle physics. Non electromagnetic spin-spin forces created through the exchange of a scalar boson (like the axion) were first suggested by Moody and Wilcek [8]. Dobrescu and Mocioiu enumerated nine possible spin-spin interactions associated with the exchange of a vector boson (like the z') that are compatible with rotational invariance [9]. Stringent limits have now been placed on the three velocity-independent interactions both at long range [1,4,5,10 ] and at atomic scales [2,3,7]. The remaining six interactions (numbered as in Ref.[9]) depend not only on the spins (�) and relative positions (r) of the two fermions, but also on their relative velocity (v).

The best upper limit for the electron electric dipole moment was recently set by the ACME collaboration. This experiment measures an electron spin-precession in a cold beam of ThO molecules in their metastable D H 3

We propose and study a method of optical crosstalk suppression for silicon photomultipliers (SiPMs) using optical filters. We demonstrate that attaching absorptive visible bandpass filters to the SiPM can substantially reduce the optical crosstalk. Measurements suggest that the absorption of near infrared light is important to achieve this suppression. The proposed technique can be easily applied to suppress the optical crosstalk in SiPMs in cases where filtering near infrared light is compatible with the application.

Experimental searches for the electron electric dipole moment, de, probe new physics beyond the Standard Model. Recently, the ACME Collaboration set a new limit of |de| < 1.1 × 10 −29 e · cm [Nature 562, 355 (2018)], constraining time reversal symmetry (T) violating physics in the 3-100 TeV energy scale. ACME extracts de from the measurement of electron spin precession due to the thorium monoxide (ThO) molecule's internal electric field. This recent ACME II measurement achieved an order of magnitude increased sensitivity over ACME I by reducing both statistical and systematic uncertainties in the measurement of the electric dipole precession frequency. The ACME II statistical uncertainty was a factor of 1.7 above the ideal shot-noise limit. We have since traced this excess noise to timing imperfections. When the experimental imperfections are eliminated, we show that shot noise limit is attained by acquiring noise-free data in the same configuration as ACME II. arXiv:1907.00554v1 [physics.atom-ph] 1 Jul 2019