A search for the solar neutrino effective magnetic moment has been performed using data from 1291.5 days exposure during the second phase of the Borexino experiment. No significant deviations from the expected shape of the electron recoil spectrum from solar neutrinos have been found, and a new upper limit on the effective neutrino magnetic moment of ${\mu }_{\nu }^{\mathrm{eff}}<{2.8\times 10}^{-11}$ ${\mu }_B$ at 90% C.L. has been set using constraints on the sum of the solar neutrino fluxes implied by the radiochemical gallium experiments. Using the limit for the effective neutrino moment, new limits for the magnetic moments of the neutrino flavor states, and for the elements of the neutrino magnetic moments matrix for Dirac and Majorana neutrinos, are derived.

We present the simultaneous measurement of the interaction rates $R_{pp}$, $R_{\mathrm{Be}}$, $R_{pep}$ of $pp$, ${}^7\mathrm{Be}$, and $pep$ solar neutrinos performed with a global fit to the Borexino data in an extended energy range (0.19–2.93) MeV with particular attention to details of the analysis methods. This result was obtained by analyzing 1291.51 days of Borexino Phase-II data, collected after an extensive scintillator purification campaign. Using counts per day $(\mathrm{cpd})/100\mathrm{ton}$ as unit, we find $R_{pp}=134\pm 10(\mathrm{stat}{)}_{-10}^{+6}(\mathrm{sys})$, $R_{Be}=48.3\pm 1.1(\mathrm{stat}{)}_{-0.7}^{+0.4}(\mathrm{sys})$; and $R_{pep}^{\mathrm{HZ}}=2.43\pm 0.36(\mathrm{stat}{)}_{-0.22}^{+0.15}(\mathrm{sys})$ assuming the interaction rate $R_{\mathrm{CNO}}$ of CNO-cycle (Carbon, Nitrogen, Oxigen) solar neutrinos according to the prediction of the high metallicity standard solar model, and $R_{pep}^{\mathrm{LZ}}=2.65\pm 0.36(\mathrm{stat}{)}_{-0.24}^{+0.15}(\mathrm{sys})$ according to that of the low metallicity model. An upper limit $R_{\mathrm{CNO}}<8.1\mathrm{cpd}/100\mathrm{ton}$ (95% C.L.) is obtained by setting in the fit a constraint on the ratio $R_{pp}/R_{pep}$ ($47.7\pm 0.8\mathrm{cpd}/100\mathrm{ton}$ or $47.5\pm 0.8\mathrm{cpd}/100\mathrm{ton}$ according to the high or low metallicity hypothesis).

We observe a deuteron beam polarization lifetime near 1000 s in the horizontal plane of a magnetic storage ring (COSY). This long spin coherence time is maintained through a combination of beam bunching, electron cooling, sextupole field corrections, and the suppression of collective effects through beam current limits. This record lifetime is required for a storage ring search for an intrinsic electric dipole moment on the deuteron at a statistical sensitivity level approaching ${10}^{-29}e\mathrm{cm}$.

A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune—defined as the number of spin precessions per turn—is given by ${\nu }_{\mathrm{s}}=\gamma G$ ($\gamma$ is the Lorentz factor, $G$ the gyromagnetic anomaly). At $970\mathrm{MeV}/c$, the deuteron spins coherently precess at a frequency of $\approx 120\mathrm{kHz}$ in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order ${10}^{-8}$, and to $1\times {10}^{-10}$ for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.

This paper presents a comprehensive geoneutrino measurement using the Borexino detector, located at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The analysis is the result of 3262.74 days of data between December 2007 and April 2019. The paper describes improved analysis techniques and optimized data selection, which includes enlarged fiducial volume and sophisticated cosmogenic veto. The reported exposure of $(1.29\pm 0.05)\times {10}^{32}\mathrm{protons}\times \mathrm{year}$ represents an increase by a factor of two over a previous Borexino analysis reported in 2015. By observing ${52.6}_{-8.6}^{+9.4}(\mathrm{stat}{)}_{-2.1}^{+2.7}(\mathrm{sys})$ geoneutrinos (68% interval) from ${}^{238}\mathrm{U}$ and ${}^{232}\mathrm{Th}$, a geoneutrino signal of ${47.0}_{-7.7}^{+8.4}({\text{stat})}_{-1.9}^{+2.4}(\mathrm{sys})$ TNU with ${}_{-17.2}^{+18.3}\%$ total precision was obtained. This result assumes the same Th/U mass ratio as found in chondritic CI meteorites but compatible results were found when contributions from ${}^{238}\mathrm{U}$ and ${}^{232}\mathrm{Th}$ were both fit as free parameters. Antineutrino background from reactors is fit unconstrained and found compatible with the expectations. The null-hypothesis of observing a geoneutrino signal from the mantle is excluded at a 99.0% C.L. when exploiting detailed knowledge of the local crust near the experimental site. Measured mantle signal of ${21.2}_{-9.0}^{+9.5}(\mathrm{stat}{)}_{-0.9}^{+1.1}(\mathrm{sys})$ TNU corresponds to the production of a radiogenic heat of ${24.6}_{-10.4}^{+11.1}\mathrm{TW}$ (68% interval) from ${}^{238}\mathrm{U}$ and ${}^{232}\mathrm{Th}$ in the mantle. Assuming 18% contribution of ${}^{40}\mathrm{K}$ in the mantle and ${8.1}_{-1.4}^{+1.9}\mathrm{TW}$ of total radiogenic heat of the lithosphere, the Borexino estimate of the total radiogenic heat of the Earth is ${38.2}_{-12.7}^{+13.6}\mathrm{TW}$, which corresponds to the convective Urey ratio of ${0.78}_{-0.28}^{+0.41}$. These values are compatible with different geological predictions, however there is a $\sim 2.4\sigma$ tension with those Earth models which predict the lowest concentration of heat-producing elements in the mantle. In addition, by constraining the number of expected reactor antineutrino events, the existence of a hypothetical georeactor at the center of the Earth having power greater than 2.4 TW is excluded at 95% C.L. Particular attention is given to the description of all analysis details which should be of interest for the next generation of geoneutrino measurements using liquid scintillator detectors.