Investigating nucleon-nucleon correlations inherent to the strong nuclear force is one of the core goals in nuclear physics research. We showcase the unique opportunities offered by collisions of 16O nuclei at high-energy facilities to reveal detailed many-body properties of the nuclear ground state. We interface existing knowledge about the geometry of 16O coming from <italic>ab-initio</italic> calculations of nuclear structure with transport simulations of high-energy 16O+ 16O collisions. Bulk observables in these processes, such as the elliptic flow or the fluctuations of the mean transverse momentum, are found to depend significantly on the input nuclear model and to be sensitive to realistic clustering and short-range repulsive correlations, effectively opening a new avenue to probe these features experimentally. This finding demonstrates collisions of oxygen nuclei as a tool to elucidate initial conditions of small collision systems while fostering connections with effective field theories of nuclei rooted in quantum chromodynamics (QCD).

United States

China

Chunjian Zhang

Jinhui Chen

Germany

Giuliano Giacalone

Shengli Huang

Jiangyong Jia

Yu-Gang Ma

<italic>Ab-initio</italic> nucleon-nucleon correlations and their impact on high energy 16O+ 16O collisions

I show that the average transverse momentum, <math><mo>〈</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>t</mi></mrow></msub><mo>〉</mo></math>, of the hadrons emitted in relativistic nuclear collisions can be used as a “knob” to control the strength of the magnetic field induced by the spectator and the participant protons over the overlap region. I thus argue that any observable sensitive to this magnetic field is nontrivially correlated with <math><mo>〈</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>t</mi></mrow></msub><mo>〉</mo></math> at a given collision centrality.

France

Turning up and down strong magnetic fields in relativistic nuclear collisions

We predict that the mean transverse momentum of charged hadrons <math><mo>〈</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>t</mi></mrow></msub><mo>〉</mo></math> rises as a function of the charged-particle multiplicity in ultracentral nucleus-nucleus collisions. We explain that this phenomenon has a simple physical origin and represents an unambiguous prediction of the hydrodynamic framework of heavy-ion collisions. We argue that the relative increase of <math><mo>〈</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>t</mi></mrow></msub><mo>〉</mo></math> is proportional to the speed of sound squared <math><msubsup><mrow><mi>c</mi></mrow><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math> of the quark-gluon plasma. Based on the value of <math><msubsup><mrow><mi>c</mi></mrow><mrow><mi>s</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math> from lattice QCD, we expect <math><mo>〈</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>t</mi></mrow></msub><mo>〉</mo></math> to increase by approximately 18 MeV between 1% and 0.001% centrality in Pb+Pb collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>5.02</mn></math> TeV

Brazil

Fernando G. Gardim

Jean-Yves Ollitrault

The mean transverse momentum of ultracentral heavy-ion collisions: A new probe of hydrodynamics

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.

CERN

Aleksas Mazeliauskas

Sören Schlichting

Hydrodynamic Attractors, Initial State Energy, and Particle Production in Relativistic Nuclear Collisions

We study the disappearance of the away-side peak of the di-hadron correlation function in <math><mrow><mi>p</mi><mo>+</mo><mi>A</mi></mrow></math> vs <math><mrow><mi>p</mi><mo>+</mo><mi>p</mi></mrow></math> collisions at forward rapidities, when the scaterring process presents a manifest dilute-dense asymmetry. We improve the state-of-the-art description of this phenomenon in the framework of the color glass condensate (CGC), for hadrons produced nearly back to back. In that case, the gluon content of the saturated nuclear target can be described with transverse-momentum-dependent gluon distributions, whose small-<math><mi>x</mi></math> evolution we calculate numerically by solving the Balitsky-Kovchegov equation with running coupling corrections. We first show that our formalism provides a good description of the disappearance of the away-side azimuthal correlations in <math><mrow><mi>d</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions observed at BNL Relativistic Heavy Ion Collider (RHIC) energies. Then, we predict the away-side peak of upcoming <math><mrow><mi>p</mi><mo>+</mo><mi>Au</mi></mrow></math> data at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>200</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> to be suppressed by about a factor 2 with respect to <math><mrow><mi>p</mi><mo>+</mo><mi>p</mi></mrow></math> collisions, and we propose to study the rapidity dependence of that suppression as a complementary strong evidence of gluon saturation in experimental data.

Spain

Javier L. Albacete

Cyrille Marquet

Czechia

Marek Matas

Forward dihadron back-to-back correlations in <math><mi>p</mi><mi>A</mi></math> collisions

Motivated by the relation existing between the gluon density in a hadron and the multiplicity of the particles measured in the final state of hadron-nucleus collisions, we study systematically the fluctuations of the gluon density in onia, which are the simplest dilute hadrons, of different sizes and at various rapidities. We argue that the small and the large-multiplicity tails of the gluon distributions present universal features, which should translate into properties of the multiplicity of the particles measured in the final state of high-energy proton-nucleus collisions, or of deep-inelastic scattering at a future electron-ion collider. We propose simple physical pictures of the rare events populating the tails of the multiplicity distribution that allow us to derive analytical formulas describing these universal behaviors, and we compare them to the results of Monte Carlo simulations.