Spectroscopic factors of neutron-hole and proton-hole states in ${}^{131}\mathrm{Sn}$ and ${}^{131}\mathrm{In}$, respectively, were measured using one-nucleon removal reactions from doubly magic ${}^{132}\mathrm{Sn}$ at relativistic energies. For ${}^{131}\mathrm{In}$, a 2910(50)-keV $\gamma$ ray was observed for the first time and tentatively assigned to a decay from a ${5/2}^{-}$ state at 3275(50) keV to the known ${1/2}^{-}$ level at 365 keV. The spectroscopic factors determined for this new excited state and three other single-hole states provide first evidence for a strong fragmentation of single-hole strength in ${}^{131}\mathrm{Sn}$ and ${}^{131}\mathrm{In}$. The experimental results are compared to theoretical calculations based on the relativistic particle-vibration coupling model and to experimental information for single-hole states in the stable doubly magic nucleus ${}^{208}\mathrm{Pb}$.

We report a 0.08% measurement of the bound neutron scattering length of ${}^4\mathrm{He}$ using neutron interferometry. The result is $b=(3.0982\pm 0.0021[\mathrm{stat}]\pm 0.0014[\mathrm{syst}])\mathrm{fm}$. The corresponding free atomic scattering length is $a=(2.4746\pm 0.0017[\mathrm{stat}]\pm 0.0011[\mathrm{syst}])\mathrm{fm}$. With this result the world average becomes $b=(3.0993\pm 0.0025)\mathrm{fm}$, a 2% downward shift and a reduction in uncertainty by more than a factor of six. Our result is in disagreement with a previous neutron interferometric measurement but is in good agreement with earlier measurements using neutron transmission.

We exploit the concept of hydrodynamic attractors to establish a macroscopic description of the early time out-of-equilibrium dynamics of high energy heavy-ion collisions. One direct consequence is a general relation between the initial state energy and the produced particle multiplicities measured in experiments. When combined with an ab initio model of energy deposition, the entropy production during the preequilibrium phase naturally explains the universal centrality dependence of the measured charged particle yields in nucleus-nucleus collisions. Further, we estimate the energy density of the far-from-equilibrium initial state and discuss how our results can be used to constrain nonequilibrium properties of the quark-gluon plasma.

We report on the measurement of the two-neutrino double-$\beta$ decay of ${}^{82}\mathrm{Se}$ performed for the first time with cryogenic calorimeters, in the framework of the CUPID-0 experiment. With an exposure of 9.95 kg yr of $\mathrm{Zn}{}^{82}\mathrm{Se}$, we determine the two-neutrino double-$\beta$ decay half-life of ${}^{82}\mathrm{Se}$ with an unprecedented precision level, $T_{1/2}^{2\nu }=[8.60\pm 0.03(\text{stat}){}_{-0.13}^{+0.19}(\text{syst})]\times {10}^{19}\mathrm{yr}$. The very high signal-to-background ratio, along with the detailed reconstruction of the background sources allowed us to identify the single state dominance as the underlying mechanism of such a process, demonstrating that the higher state dominance hypothesis is disfavored at the level of $5.5\sigma$.

We perform a global sensitivity analysis of the binding energy and the charge radius of the nucleus ${}^{16}\mathrm{O}$ to identify the most influential low-energy constants in the next-to-next-to-leading order chiral Hamiltonian with two- and three-nucleon forces. For this purpose, we develop a subspace-projected coupled-cluster method using eigenvector continuation [Frame D. et al., Phys. Rev. Lett. 121, 032501 (2018)]. With this method, we compute the binding energy and charge radius of ${}^{16}\mathrm{O}$ at more than $10^6$ different values of the 16 low-energy constants in one hour on a standard laptop computer. For relatively small subspace projections, the root-mean-square error is about 1% compared to full-space coupled-cluster results. We find that 58(1)% of the variance in energy can be apportioned to a single contact term in the ${}^3{S}_1$ wave, whereas the radius depends sensitively on several low-energy constants and their higher-order correlations. The results identify the most important parameters for describing nuclear saturation and help prioritize efforts for uncertainty reduction of theoretical predictions. The achieved acceleration opens up an array of computational statistics analyses of the underlying description of the strong nuclear interaction in nuclei across the Segrè chart.

Collisions between complex nuclei may give rise to their total or partial fusion. The latter case is found experimentally to gain importance when one of the colliding nuclei is weakly bound. It has been commonly assumed that the partial fusion mechanism is a two-step process, whose first step is the dissociation of the weakly bound nucleus, followed by the capture of one of the fragments. To assess this interpretation, we present the first implementation of the three-body model of inclusive breakup proposed in the 1980s by Austern et al. [Phys. Rep. 154, 125 (1987)] that accounts for both the direct, one-step, partial fusion and the two-step mechanism proceeding via the projectile continuum states. Contrary to the widely assumed picture, we find that, at least for the investigated cases, the partial fusion is largely dominated by the direct capture from the projectile ground state.

The nuclear response theory for charge-exchange modes in the relativistic particle-vibration coupling approach is extended to include for the first time particle-vibration coupling effects in the ground state of the parent nucleus. In a framework based on the effective meson-nucleon Lagrangian, we investigate the role of such complex ground-state correlations in the description of Gamow-Teller transitions in ${}^{90}\mathrm{Zr}$ in both ($p$, $n$) and ($n$, $p$) channels. The particle-vibration coupling effects are calculated without introducing new parameters. We find that this new correlation mechanism is fully responsible for the appearance of the strength in the ($n$, $p$) branch. Comparison of our results to the available experimental data shows a very good agreement up to excitation energies beyond the giant resonance region when taking into account a phenomenological admixture of the isovector spin monopole transitions. The parent-daughter binding-energy differences are also greatly improved by the inclusion of the new correlations.

Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer $Q^2$: 0.10, 0.20, and $0.45{\mathrm{GeV}}^2$, at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion relations allowed the extraction of the structure functions $P_{LL}-P_{TT}/\epsilon$ and $P_{LT}$, as well as the electric and magnetic generalized polarizabilities ${\alpha }_{E1}(Q^2)$ and ${\beta }_{M1}(Q^2)$. These new results show a smooth and rapid falloff of ${\alpha }_{E1}(Q^2)$, in contrast to previous measurements at $Q^2=0.33{\mathrm{GeV}}^2$, and provide for the first time a precise mapping of ${\beta }_{M1}(Q^2)$ in the low-$Q^2$ region.

The first measurement of the $\mathrm{\Upsilon }(1S)$ elliptic flow coefficient ($v_2$) is performed at forward rapidity ($2.5<y<4$) in Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ with the ALICE detector at the LHC. The results are obtained with the scalar product method and are reported as a function of transverse momentum ($p_T$) up to $15\mathrm{GeV}/c$ in the 5%–60% centrality interval. The measured $\mathrm{\Upsilon }(1S)v_2$ is consistent with 0 and with the small positive values predicted by transport models within uncertainties. The $v_2$ coefficient in $2<p_T<15\mathrm{GeV}/c$ is lower than that of inclusive $J/\psi$ mesons in the same $p_T$ interval by 2.6 standard deviations. These results, combined with earlier suppression measurements, are in agreement with a scenario in which the $\mathrm{\Upsilon }(1S)$ production in Pb–Pb collisions at LHC energies is dominated by dissociation limited to the early stage of the collision, whereas in the $J/\psi$ case there is substantial experimental evidence of an additional regeneration component.

Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave function. In this Letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive $\omega$ electroproduction off the proton, $ep\to e^{\prime }p\omega$, at central $Q^2$ values of 1.60, $2.45{\mathrm{GeV}}^2$, at $W=2.21\mathrm{GeV}$. The results of our pioneering $-u\approx -u_{\min }$ study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full $L/T/LT/TT$ separations in this never explored kinematic territory. At $Q^2=2.45{\mathrm{GeV}}^2$, the observed dominance of ${\sigma }_T$ over ${\sigma }_L$, is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes: universal nonperturbative objects only accessible through backward-angle kinematics.

We present a sampling method for the transition from relativistic hydrodynamics to particle transport, commonly referred to as particlization, which preserves the local conservation of energy, momentum, baryon number, strangeness, and electric charge microcanonically, i.e., in every sample. The proposed method is essential for studying fluctuations and correlations by means of stochastic hydrodynamics. It is also useful for studying small systems. The method is based on Metropolis sampling applied to particles within distinct patches of the switching space-time surface, where hydrodynamic and kinetic evolutions are matched.

The weak decay parameter ${\alpha }_{-}$ of the $\mathrm{\Lambda }$ is an important quantity for the extraction of polarization observables in various experiments. Moreover, in combination with ${\alpha }_{+}$ from $\overline{\mathrm{\Lambda }}$ decay it provides a measure for matter-antimatter asymmetry. The weak decay parameter also affects the decay parameters of the $\mathrm{\Xi }$ and $\mathrm{\Omega }$ baryons and, in general, any quantity in which the polarization of the $\mathrm{\Lambda }$ is relevant. The recently reported value by the BESIII Collaboration of 0.750(9)(4) is significantly larger than the previous PDG value of 0.642(13) that had been accepted and used for over 40 years. In this work we make an independent estimate of ${\alpha }_{-}$, using an extensive set of polarization data measured in kaon photoproduction in the baryon resonance region and constraints set by spin algebra. The obtained value is 0.721(6)(5). The result is corroborated by multiple statistical tests as well as a modern phenomenological model, showing that our new value yields the best description of the data in question. Our analysis supports the new BESIII finding that ${\alpha }_{-}$ is significantly larger than the previous PDG value. Any experimental quantity relying on the value of ${\alpha }_{-}$ should therefore be reconsidered.

We show that the recent proposal to describe the $N_f=1$ baryon in the large number of the color limit as a quantum Hall droplet can be understood as a chiral bag in a ($1+2$)-dimensional strip using the Cheshire Cat principle. For a small bag radius, the bag reduces to a vortex line which is the smile of the cat with flowing gapless quarks all spinning in the same direction. The disk enclosed by the smile is described by a topological field theory due to the Callan-Harvey anomaly outflow. The chiral bag naturally carries the unit baryon number and spin $\frac{1}{2}{N}_c$. The generalization to arbitrary $N_f$ is discussed.

We report the first measurement of rapidity-odd directed flow ($v_1$) for $D^0$ and $\overline{D^0}$ mesons at midrapidity ($|y|<0.8$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ using the STAR detector at the Relativistic Heavy Ion Collider. In 10–80% $\mathrm{Au}+\mathrm{Au}$ collisions, the slope of the $v_1$ rapidity dependence ($d{v}_1/dy$), averaged over $D^0$ and $\overline{D^0}$ mesons, is $-0.080\pm 0.017(\text{stat})\pm 0.016(\text{syst})$ for transverse momentum $p_T$ above $1.5\mathrm{GeV}/c$. The absolute value of $D^0$ meson $d{v}_1/dy$ is about 25 times larger than that for charged kaons, with $3.4\sigma$ significance. These data give a unique insight into the initial tilt of the produced matter, and offer constraints on the geometric and transport parameters of the hot QCD medium created in relativistic heavy-ion collisions.

Measurements of anisotropic flow coefficients ($v_n$) and their cross-correlations using two- and multiparticle cumulant methods are reported in collisions of $pp$ at $\sqrt{s}=13\mathrm{TeV}$, $p\text{−}\mathrm{Pb}$ at a center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$, Xe-Xe at $\sqrt{s_{\mathrm{NN}}}=5.44\mathrm{TeV}$, and Pb-Pb at $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$ recorded with the ALICE detector. The multiplicity dependence of $v_n$ is studied in a very wide range from 20 to 3000 particles produced in the midrapidity region $|\eta |<0.8$ for the transverse momentum range $0.2<p_T<3.0\mathrm{GeV}/c$. An ordering of the coefficients $v_2>v_3>v_4$ is found in $pp$ and $p\text{−}\mathrm{Pb}$ collisions, similar to that seen in large collision systems, while a weak $v_2$ multiplicity dependence is observed relative to nucleus-nucleus collisions in the same multiplicity range. Using a novel subevent method, $v_2$ measured with four-particle cumulants is found to be compatible with that from six-particle cumulants in $pp$ and $p\text{−}\mathrm{Pb}$ collisions. The magnitude of the correlation between $v_n^2$ and $v_m^2$, evaluated with the symmetric cumulants $\mathrm{SC}(m,n)$ is observed to be positive at all multiplicities for $v_2$ and $v_4$, while for $v_2$ and $v_3$ it is negative and changes sign for multiplicities below 100, which may indicate a different $v_n$ fluctuation pattern in this multiplicity range. The observed long-range multiparticle azimuthal correlations in high multiplicity $pp$ and $p\text{−}\mathrm{Pb}$ collisions can neither be described by pythia 8 nor by impact-parameter-Glasma, music, and ultrarelativistic quantum molecular dynamics model calculations, and hence, provide new insights into the understanding of collective effects in small collision systems.