The long-range collective flow of particles produced in oxygen-oxygen (OO) and neon-neon (NeNe) collisions is measured with the CMS detector at the CERN LHC. The data samples were collected at a center-of-mass energy per nucleon pair of 5.36 TeV, with integrated luminosities of 7 nb$^{-1}$ and 0.8 nb$^{-1}$ for OO and NeNe collisions, respectively. Two- and four-particle azimuthal correlations are measured over nearly five units of pseudorapidity. Significant elliptic ($v_2$) and triangular ($v_3$) flow harmonics are observed in both systems. The ratios of $v_n$ coefficients between NeNe and OO collisions reveal sensitivity to quadrupole correlations in the nuclear wave functions. Hydrodynamic models with $\textit{ab initio}$ nuclear structure inputs qualitatively reproduce the collision-overlap dependence of both the $v_n$ values and the NeNe to OO ratios. These measurements provide new constraints on hydrodynamic models for small collision systems and offer valuable input on the nuclear structure of $^{16}$O and $^{20}$Ne.
The $v_{2}\{2,\lvert\Delta\eta\rvert>2\}$, $v_{3}\{2,\lvert\Delta\eta\rvert>2\}$ and $v_{2}\{4\}$ values for charged particles as functions of centrality in OO collisions at 5.36 TeV.
The $v_{2}\{2,\lvert\Delta\eta\rvert>2\}$, $v_{3}\{2,\lvert\Delta\eta\rvert>2\}$ and $v_{2}\{4\}$ values for charged particles as functions of centrality in NeNe collisions at 5.36 TeV.
The $v_{2}\{2,\lvert\Delta\eta\rvert>2\}$ and $v_{2}\{4\}$ ratios for charged particles as functions of centrality in NeNe to OO collisions at 5.36 TeV.
The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive $\pi ^0$ and $\eta $ photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the $\gamma p \rightarrow \pi ^0 p$ and $\gamma p \rightarrow \eta p$ reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the $\eta n$ system at $W = 1.68\ \textrm{GeV}$. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the $S_{11}(1535)$ and $S_{11}(1650)$ resonances within the $S_{11}$-partial wave.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \pi^0 p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma n \to \pi^0 n$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \eta p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
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