Collective effects in strong interaction processes: experimental highlights

TL;DR

The paper surveys collective phenomena in strong interactions across collision systems from $p+p$ to heavy ions over wide energies, emphasizing how jet production, anisotropic flow, and femtoscopy reveal the space-time evolution and transport properties of QCD matter. It consolidates multi-TeV jet measurements, dead-cone observations, and top-quark production in nuclear collisions with jet quenching patterns that depend on color charge and quark mass, while also outlining hydrodynamic-like flow signals and constraints on $\tilde{\eta}/s$. Additionally, it discusses topological effects such as CME/CMW, their experimental upper limits in isobar and small systems, and the role of femtoscopy in constraining hyperon–nucleon interactions relevant for neutron-star equations of state, along with possible connections to Bose–Einstein condensation and cosmic-ray muon anomalies. The work highlights the interdisciplinary impact on astrophysics and cosmology and points to advancing initial-state modeling as crucial for interpreting anisotropic flow across systems.

Abstract

Collective effects are reviewed for collisions of various systems - from proton-proton to heavy ion - in wide energy range. In proton-proton interactions studies of hadron jets devote to the better understanding of some basic features of strong interaction and search for the physics beyond of Standard Model. First results have been obtained for massive gauge bosons and antitop-top pair production in proton-nuclear and heavy ion collisions at multi-TeV energies. The collectivity has been observed for various particle and beam species, in particular, in collision of small systems. Experimental results obtained for discrete symmetries of strong interaction at finite temperature confirm indirectly the topologically non-trivial structure of the vacuum. The recent measurements of femtoscopic correlations provide, in particular, the indirect estimations for parameters of hyperon-nucleon potentials which are essential for study of inner structure of compact astrophysical objects. Novel mechanism for multiparticle production due to collectivity can be expected in very high energy nuclear collisions and it may be helpful for better understanding of the nature of the muon puzzle in ultra-high energy cosmic ray measurements. Thus studies of collective effects in strong interaction processes provide new important results for relativistic astrophysics, cosmology and cosmic ray physics, i.e. have interdisciplinary significance.

Figures (1)

• Figure 1: Parameters $z_{\pi}^{(n)}$ (a, b) and $\Delta z_{\pi}^{(n)}$ (c, d) in dependence on energy. In the case of a symmetric ($A+A$) ion collisions the approximation $\langle N_{\scriptsize{\hbox{ch}}}^{AA}\rangle_{1}$ is used for the panels (a, c) while $\langle N_{\scriptsize{\hbox{ch}}}^{AA}\rangle_{2}$ is used for the panels (b, d). In each panel solid lines correspond to the $\langle N_{\scriptsize{\hbox{ch}}}^{pp}\rangle_{1}$, dashed lines are for $\langle N_{\scriptsize{\hbox{ch}}}^{pp}\rangle_{2}$. Effect of BEC is taken into account in accordance with the relation for the mean value $n(X)$ shown in the main text for energy region with $\langle n_{\scriptsize{\hbox{ch}}}\rangle > n_{\scriptsize{\hbox{ch,c}}}$ in certain type of collisions if any. The upper collection of curves are for $X=2$, lower curves are for $X=5$Okorokov-PAN-87-172-2024.