We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction ${{}^3\mathrm{He}}^{\uparrow }(e,e^{\prime })X$ on a polarized ${}^3\mathrm{He}$ gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be nonzero if two-photon-exchange contributions are included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron beam, covers a range of $1.7<W<2.9\mathrm{GeV}$, $1.0<Q^2<4.0{\mathrm{GeV}}^2$ and $0.16<x<0.65$. Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-${}^3\mathrm{He}$ cross-section ratios. The measured neutron asymmetries are negative with an average value of $(-1.09\pm 0.38)\times 10^{-2}$ for invariant mass $W>2\mathrm{GeV}$, which is nonzero at the $2.89\sigma$ level. Our measured asymmetry agrees both in sign and magnitude with a two-photon-exchange model prediction that uses input from the Sivers transverse momentum distribution obtained from semi-inclusive deep-inelastic scattering.

This Letter reports on a systematic study of $\beta$-decay half-lives of neutron-rich nuclei around doubly magic ${}^{208}\mathrm{Pb}$. The lifetimes of the 126-neutron shell isotone ${}^{204}\mathrm{Pt}$ and the neighboring ${}^{200–202}\mathrm{Ir}$, ${}^{203}\mathrm{Pt}$, ${}^{204}\mathrm{Au}$ are presented together with other 19 half-lives measured during the “stopped beam” campaign of the rare isotope investigations at GSI collaboration. The results constrain the main nuclear theories used in calculations of $r$-process nucleosynthesis. Predictions based on a statistical macroscopic description of the first-forbidden $\beta$ strength reveal significant deviations for most of the nuclei with $N<126$. In contrast, theories including a fully microscopic treatment of allowed and first-forbidden transitions reproduce more satisfactorily the trend in the measured half-lives for the nuclei in this region, where the r-process pathway passes through during $\beta$ decay back to stability.

Measurements of the excitation function for the fusion of ${}^{24}\mathrm{Mg}+{}^{30}\mathrm{Si}$ $(Q=17.89\mathrm{MeV})$have been extended toward lower energies with respect to previous experimental data. The $S$-factor maximum observed in this large, positive-$Q$-value system is the most pronounced among such systems studied thus far. The significance and the systematics of an $S$-factor maximum in systems with positive fusion $Q$ values are discussed. This result would strongly impact the extrapolated cross sections and reaction rates in the carbon and oxygen burnings and, thus, the study of the history of stellar evolution.

We report the STAR measurements of dielectron ($e^{+}{e}^{-}$) production at midrapidity ($|y_{ee}|<1$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The measurements are evaluated in different invariant mass regions with a focus on 0.30–0.76 ($\rho$-like), 0.76–0.80 ($\omega$-like), and 0.98–1.05 ($\varphi$-like) $\mathrm{GeV}/{\mathrm{c}}^2$. The spectrum in the $\omega$-like and $\varphi$-like regions can be well described by the hadronic cocktail simulation. In the $\rho$-like region, however, the vacuum $\rho$ spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of $1.77\pm 0.11(\text{stat})\pm 0.24(\text{syst})\pm 0.33(\text{cocktail})$ is determined with respect to the hadronic cocktail simulation that excludes the $\rho$ meson. The excess yield in the $\rho$-like region increases with the number of collision participants faster than the $\omega$ and $\varphi$ yields. Theoretical models with broadened $\rho$ contributions through interactions with constituents in the hot QCD medium provide a consistent description of the dilepton mass spectra for the measurement presented here and the earlier data at the Super Proton Synchrotron energies.

We studied simultaneously the ${}^4\mathrm{He}(e,e^{\prime }p)$, ${}^4\mathrm{He}(e,e^{\prime }pp)$, and ${}^4\mathrm{He}(e,e^{\prime }pn)$ reactions at $Q^2=2(\mathrm{GeV}/c{)}^2$ and $x_B>1$, for an $(e,e^{\prime }p)$ missing-momentum range of 400 to $830\mathrm{MeV}/c$. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual $A=2$ system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum, in a region where the nucleon-nucleon ($NN$) force is expected to change from predominantly tensor to repulsive. The abundance of neutron-proton pairs is reduced as the nucleon momentum increases beyond $\sim 500\mathrm{MeV}/c$. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum. Our data are compared with calculations of two-nucleon momentum distributions in ${}^4\mathrm{He}$ and discussed in the context of probing the elusive repulsive component of the $NN$ force.

The properties of pygmy dipole states in ${}^{208}\mathrm{Pb}$ were investigated using the ${}^{208}\mathrm{Pb}$(${}^{17}\mathrm{O}$, ${}^{17}\mathrm{O}’\gamma$) reaction at 340 MeV and measuring the $\gamma$ decay with high resolution with the AGATA demonstrator array. Cross sections and angular distributions of the emitted $\gamma$ rays and of the scattered particles were measured. The results are compared with ($\gamma$, ${\gamma }^{\prime }$) and ($p$, $p^{\prime }$) data. The data analysis with the distorted wave Born approximation approach gives a good description of the elastic scattering and of the inelastic excitation of the $2^{+}$ and $3^{-}$ states. For the dipole transitions a form factor obtained by folding a microscopically calculated transition density was used for the first time. This has allowed us to extract the isoscalar component of the $1^{-}$ excited states from 4 to 8 MeV.

The PHENIX experiment has measured open heavy-flavor production via semileptonic decay over the transverse momentum range $1<p_T<6\mathrm{GeV}/c$ at forward and backward rapidity ($1.4<|y|<2.0$) in $d+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. In central $d+\mathrm{Au}$ collisions, relative to the yield in $p+p$ collisions scaled by the number of binary nucleon-nucleon collisions, a suppression is observed at forward rapidity (in the $d$-going direction) and an enhancement at backward rapidity (in the Au-going direction). Predictions using nuclear-modified-parton-distribution functions, even with additional nuclear-$p_T$ broadening, cannot simultaneously reproduce the data at both rapidity ranges, which implies that these models are incomplete and suggests the possible importance of final-state interactions in the asymmetric $d+\mathrm{Au}$ collision system. These results can be used to probe cold-nuclear-matter effects, which may significantly affect heavy-quark production, in addition to helping constrain the magnitude of charmonia-breakup effects in nuclear matter.

The Gamow-Teller strength in the ${\beta }^{+}$ direction to ${}^{46}\mathrm{Sc}$ was extracted via the ${}^{46}\mathrm{Ti}(t,{}^3\mathrm{He}+\gamma )$ reaction at $115\mathrm{MeV}/u$. The $\gamma$-ray coincidences served to precisely measure the very weak Gamow-Teller transition to a final state at 991 keV. Although this transition is weak, it is crucial for accurately estimating electron-capture rates in astrophysical scenarios with relatively low stellar densities and temperatures, such as presupernova stellar evolution. Shell-model calculations with different effective interactions in the pf shell-model space do not reproduce the experimental Gamow-Teller strengths, which is likely due to $sd$-shell admixtures. Calculations in the quasiparticle random phase approximation that are often used in astrophysical simulations also fail to reproduce the experimental Gamow-Teller strength distribution, leading to strongly overestimated electron-capture rates. Because reliable theoretical predictions of Gamow-Teller strengths are important for providing astrophysical electron-capture reaction rates for a broad set of nuclei in the lower pf shell, we conclude that further theoretical improvements are required to match astrophysical needs.

Cross sections of $1n$-removal reactions from the neutron-rich nucleus ${}^{37}\mathrm{Mg}$ on C and Pb targets and the parallel momentum distributions of the ${}^{37}\mathrm{Mg}$ residues from the C target have been measured at $240\mathrm{MeV}/\text{nucleon}$. A combined analysis of these distinct nuclear- and Coulomb-dominated reaction data shows that the ${}^{37}\mathrm{Mg}$ ground state has a small $1n$ separation energy of ${0.22}_{-0.09}^{+0.12}\mathrm{MeV}$ and an appreciable $p$-wave neutron single-particle strength. These results confirm that ${}^{37}\mathrm{Mg}$ lies near the edge of the “island of inversion” and has a sizable $p$-wave neutron halo component, the heaviest such system identified to date.

We show that a fluid dynamical scenario, already well tested against identified particle $p_t$ spectra, describes quantitatively the observed mass splitting of the elliptical flow coefficients $v_2$ for pions and protons. This provides a strong argument in favor of the existence of a fluid dynamical expansion in $p\text{−}\mathrm{Pb}$ collisions at 5.02 TeV.

Charged-pion-interferometry measurements were made with respect to the second- and third-order event plane for $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. A strong azimuthal-angle dependence of the extracted Gaussian-source radii was observed with respect to both the second- and third-order event planes. The results for the second-order dependence indicate that the initial eccentricity is reduced during the medium evolution, which is consistent with previous results. In contrast, the results for the third-order dependence indicate that the initial triangular shape is significantly reduced and potentially reversed by the end of the medium evolution, and that the third-order oscillations are largely dominated by the dynamical effects from triangular flow.

We report the observation of a very exotic decay mode at the proton drip line, the $\beta$-delayed $\gamma$-proton decay, clearly seen in the $\beta$ decay of the $T_z=-2$ nucleus ${}^{56}\mathrm{Zn}$. Three $\gamma$-proton sequences have been observed after the $\beta$ decay. Here this decay mode, already observed in the $sd$ shell, is seen for the first time in the $fp$ shell. Both $\gamma$ and proton decays have been taken into account in the estimation of the Fermi and Gamow-Teller strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.

The ${\frac{1}{2}}^{+}\to {\frac{1}{2}}^{+}$ superallowed mixed mirror decay of ${}^{19}\mathrm{Ne}$ to ${}^{19}\mathrm{F}$ is excellently suited for high precision studies of the weak interaction. However, there is some disagreement on the value of the half-life. In a new measurement we have determined this quantity to be $T_{1/2}=17.2832\pm 0.0051_{\text{(stat)}}\pm 0.0066_{\text{(syst)}}\mathrm{s}$, which differs from the previous world average by 3 standard deviations. The impact of this measurement on limits for physics beyond the standard model such as the presence of tensor currents is discussed.

Exclusive and kinematically complete high-statistics measurements of quasifree polarized $\overrightarrow{n}p$ scattering have been performed in the energy region of the narrow resonancelike structure $d^{*}$ with $I(J^P)=0(3^{+})$, $M\approx 2380\mathrm{MeV}$, and $\mathrm{\Gamma }\approx 70\mathrm{MeV}$ observed recently in the double-pionic fusion channels $pn\to d{\pi }^0{\pi }^0$ and $pn\to d{\pi }^{+}{\pi }^{-}$. The experiment was carried out with the WASA detector setup at COSY having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process $\overrightarrow{d}p\to np+p_{\text{spectator}}$. This allowed the $np$ analyzing power, $A_y$, to be measured over a broad angular range. The obtained $A_y$ angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new $A_y$ data into the SAID analysis produces a pole in the ${}^3{D}_3-{}^3{G}_3$ waves in support of the $d^{*}$ resonance hypothesis.

We examine uncertainties in the analysis of the reactor neutrino anomaly, wherein it is suggested that only about 94% of the emitted antineutrino flux was detected in short baseline experiments. We find that the form of the corrections that lead to the anomaly are very uncertain for the 30% of the flux that arises from forbidden decays. This uncertainty was estimated in four ways, is as large as the size of the anomaly, and is unlikely to be reduced without accurate direct measurements of the antineutrino flux. Given the present lack of detailed knowledge of the structure of the forbidden transitions, it is not possible to convert the measured aggregate fission beta spectra to antineutrino spectra to the accuracy needed to infer an anomaly. Neutrino physics conclusions based on the original anomaly need to be revisited, as do oscillation analyses that assumed that the antineutrino flux is known to better than approximately 4%.

The nature of the chiral candidate bands in ${}^{106}\mathrm{Ag}$, one of only two known examples of candidates which actually cross, is investigated experimentally and theoretically. Lifetimes have been determined for these bands in ${}^{106}\mathrm{Ag}$ using the Doppler-shift attenuation method with the $\gamma$-detector array AFRODITE. The level scheme of ${}^{106}\mathrm{Ag}$ has been extended, and three negative-parity bands have been observed to high spins. Configurations were assigned to the negative-parity bands based on a quasiparticle alignment analysis and on configuration-fixed constrained relativistic mean field calculations. The excitation energies, $B(M1)$ and $B(E2)$ values, as well as $B(M1)/B(E2)$ ratios have been compared with results of particle-rotor model calculations. From the investigations, it is concluded that the three close-lying negative-parity bands are a two-quasiparticle high-$K$ band and a pair of four-quasiparticle bands. The proposal that the two lowest-lying bands are chiral partners has not been confirmed.

The lifetimes of the excited levels for the two nearly degenerate bands of ${}^{106}\mathrm{Ag}$ have been measured using the Doppler-shift attenuation method. The deduced $B(E2)$ and $B(M1)$ rates in the two bands are found to be similar, except around the band crossing spin, while their moments of inertia are quite different. This is a novel observation for a nearly degenerate doublet band.