Few-gluon interactions and multipole radiation in high energy nuclear collisions

Abstract

Broad claims have been made over years about achievement of quark-gluon plasma (QGP) formation in high-energy heavy-ion collisions based on certain phenomena anticipated for QGP formation. More recently, similar phenomena have appeared in smaller collision systems. In response, the original narrative associated with QGP formation has been altered, with introduction of novel concepts such as ``QGP droplets'' appearing even in p-p collisions. In contrast, alternative research has revealed novel aspects of p-p and p-Pb collisions such as exclusivity for N-N interactions and consequences of time dilation for interacting partons. Collision geometry for A-B collisions has also been shifted from conventional Glauber Monte Carlo simulations (strongly biased) to inversion of ensemble-mean $\bar p_t$ data. The present study demonstrates that jet production dominates all aspects of $p_t$ spectrum structure and minimum-bias angular correlations over the full $p_t$ range of accessible data. Recently, progress has been made on interpretation of azimuth quadrupole ($v_2$) data, reexpressed in terms of total correlated-pair number as an extensive measure, leading to inference of quadrupole $m_t$ spectra and quadrupole amplitude variation across all A-B collision systems that show strong indication of the effects of exclusivity. The same approach applied to jet angular correlations shows similar trends. A comprehensive quantitative description of the two QCD phenomena across all collision systems has emerged. The underlying processes are few-gluon interactions producing characteristic correlation structures corresponding to color-dipole (two-gluon, dijet) and color-quadrupole (three-gluon) radiation. That description does not rely on any role for a dense medium, multiple scattering, QGP droplets or hydro theory. It applies the same rules uniformly to small and large collision systems.