An intense 120 GeV proton beam incident on an extremely long iron target generates enormous numbers of light-mass particles that also decay within that target. If one of these particles decays to a final state with a hidden gauge boson, or if such a particle is produced as a result of the initial collision, then that weakly interacting hidden-sector particle may traverse the remainder of the target and be detected downstream through its possible decay to an $e^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{-}$, or ${\pi }^{+}{\pi }^{-}$ final state. These conditions can be realized through an extension of the SeaQuest experiment at Fermilab, and in this initial investigation we consider how it can serve as an ultrasensitive probe of hidden vector gauge forces, both Abelian and non-Abelian. A light, weakly coupled hidden sector may well explain the dark matter established through astrophysical observations, and the proposed search can provide tangible evidence for its existence—or, alternatively, constrain a “sea” of possibilities.

We examine the role of $B^0\left(B^0\right)\to \sigma {\pi }^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$ decay in the Dalitz plot analysis of $B^0\left(B^0\right)\to \rho \overrightarrow{\pi }{\pi }^{+}{\pi }^{-}{\pi }^0$ decays, employed to extract the CKM parameter $\alpha .$ The $\sigma \pi$ channel is significant because it can break the relationship between the penguin contributions in $\overrightarrow{B}{\rho }^0{\pi }^0,$ $\overrightarrow{B}{\rho }^{+}{\pi }^{-},$ and $\overrightarrow{B}{\rho }^{-}{\pi }^{+}$ decays consequent to an assumption of isospin symmetry. Its presence thus mimics the effect of isospin violation. The $\sigma {\pi }^0$ state is of definite $CP,$ however; we demonstrate that the $\overrightarrow{B}\rho \pi$ analysis can be generalized to include this channel without difficulty. The $\sigma$ or $f_0\left(400\mathrm{}-1200\right)$ “meson” is a broad $I=J=0\mathrm{}$ enhancement driven by strong $\pi \pi$ rescattering; a suitable scalar form factor is constrained by the chiral dynamics of low-energy hadron-hadron interactions—it is rather different from the relativistic Breit-Wigner form adopted in earlier $\overrightarrow{B}\sigma \pi$ and $\overrightarrow{D}\sigma \pi$ analyses. We show that the use of this scalar form factor leads to an improved theoretical understanding of the measured ratio $\mathrm{Br}(B^0\to {\rho }^{\mp }{\pi }^{\pm })/\mathrm{Br}{(B}^{-}\to {\rho }^0{\pi }^{-}).\mathrm{}$

The correlation coefficients $a$, $A$, and $B$ in neutron $\beta$ decay are proportional to the ratio of the axial-vector-to-vector weak coupling constants, $g_A{/g}_V$, to leading recoil order. With the advent of the next generation of neutron-decay experiments, the recoil-order corrections to these expressions become experimentally accessible, admitting a plurality of standard model (SM) tests. The measurement of both $a$ and $A$, e.g., allows one to test the conserved-vector-current (CVC) hypothesis and to search for second-class currents (SCC) independently. The anticipated precision of these measurements suggests that the bounds on CVC violation and SCC from studies of nuclear $\beta$ decay can be qualitatively bettered.

The neutron lifetime anomaly has been used to motivate the introduction of new physics with hidden-sector particles coupled to baryon number, and on which neutron stars provide powerful constraints. Although the neutron lifetime anomaly may eventually prove to be of mundane origin, we use it as motivation for a broader review of the ways that baryon number violation, be it real or apparent, and dark sectors can intertwine and how neutron star observables, both present and future, can constrain them.

We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey’s footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.

We assess the ability of future neutron $\beta$ decay measurements of up to $\mathcal{O}\left({10}^{-4}\right)$ precision to falsify the standard model, particularly the $V-A$ law, and to identify the dynamics beyond it. To do this, we employ a maximum likelihood statistical framework which incorporates both experimental and theoretical uncertainties. Using illustrative combined global fits to Monte Carlo pseudodata, we also quantify the importance of experimental measurements of the energy dependence of the angular correlation coefficients as input to such efforts, and we determine the precision to which ill known “second-class” hadronic matrix elements must be determined in order to exact such tests.