The First Moment of Azimuthal Anisotropy in Nuclear Collisions from AGS to LHC Energies

We review topics related to the first moment of azimuthal anisotropy ($v_1$), commonly known as directed flow, focusing on both charged particles and identified particles from heavy-ion collisions. Beam energies from the highest available, at the CERN LHC, down to projectile kinetic energies per nucleon of a few GeV per nucleon, as studied in experiments at the Brookhaven AGS, fall within our scope. We focus on experimental measurements and on theoretical work where direct comparisons with experiment have been emphasized. The physics addressed or potentially addressed by this review topic includes the study of Quark Gluon Plasma, and more generally, investigation of the Quantum Chromodynamics phase diagram and the equation of state describing the accessible phases.Comment: Accepted for publication in Advances in High Energy Physic

Thiol–Ene Chemistry: A Greener Approach to Making Chemically and Thermally Stable Fibers

Fibers of micrometer and submicrometer diameters have been of significant interest in recent years owing to their advanced applications in diverse fields such as optoelectronics, regenerative medicine, piezoelectrics, ceramic materials, etc. There are a number of processes to make thin fibers including electrospinning, melt blowing, and recently developed Forcespinning. However, use of solvents or heat to lower viscosity for processing is common to all existing polymer fiber manufacturing methods, and a greener approach to making fibers remains a challenge. Interestingly, nature has engineered spiders and silkworms with a benign way of making mechanically strong and tough fibers through an intricate self-assembly of protein constituents during the fiber formation process. Comprehending the biosynthetic process and precisely replicating it has been a challenging task. However, we find that extruding small functional segments into solid fibrillar structures, through mediation of chemical interactions between the subunits, is a design approach that can be broadly adapted from nature to realize a greener fiber manufacturing process. Using the robust chemistry of thiol–ene photopolymerization, we demonstrate here that a photocurable mixture of a multifunctional acrylate, a tetrafunctional thiol, and a photoinitiator can be processed into continuous fibers by <i>in situ</i> photopolymerization during electrospinning under ambient conditions. The fibers are mechanically robust and have excellent chemical and thermal stability. While electrospinning has been used to demonstrate this concept, the chemistry could be broadly adapted into other fiber manufacturing methods to produce fibers without using solvents or heat

Hyperon Polarization along the Beam Direction Relative to the Second and Third Harmonic Event Planes in Isobar Collisions at <math display="inline"><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>200</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>

The polarization of Λ and Λ¯ hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at sNN=200  GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild pT dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagrees with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and pT dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy.The polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild $p_T$ dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagree with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and $p_T$ dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy