- The paper demonstrates collectivity in high-multiplicity pp collisions through detailed analysis of azimuthal anisotropy harmonics (v2 and v3).
- It employs advanced multi-particle correlation techniques, including four- and six-particle cumulants, to precisely measure angular correlations.
- The findings, such as the observed mass ordering in v2, challenge traditional models by showing fluid-like behavior even in small collision systems.
Analysis of Collectivity in Proton-Proton Collisions at the LHC
The paper discusses findings from an investigation into proton-proton (pp) collisions at various energies (5, 7, and 13 TeV) explored at the Large Hadron Collider (LHC). The paper extends prior research on collectivity phenomena traditionally observed in larger systems such as proton-lead and lead-lead collisions.
Central to this research are the angular correlations between particles produced in high-multiplicity pp collisions. These correlations are quantified using the second-order (v2) and third-order (v3) azimuthal anisotropy harmonics. In particular, the paper reveals a mass ordering effect observable in the v2 values, where lighter particles exhibit stronger azimuthal anisotropy, aligning with the behavior recorded in larger collision systems.
Notably, the analysis employs a sophisticated multi-particle correlation approach, introducing a novel usage of four- and six-particle correlations in detecting these harmonics. The results suggest that the observed long-range correlations are indicative of collective motion, rather than being dominantly influenced by traditional sources such as jets. This conclusion is underpinned by observations of v2 harmonics derived from cumulant analyses up to the sixth order, supporting a cohesive fluid-like behavior in the medium created by these high-energy collisions.
The implications of these findings are significant. They challenge existing theoretical frameworks which assume collectivity arises exclusively in large systems due to their capability to form a dense, thermalized medium. Here, the evidence suggests that even systems as small as pp collisions can exhibit similar collective behaviors under appropriate conditions.
The paper delivers robust numerical results, drawing direct comparisons across different energies and collision systems to underline patterns and deviations. For example, the azimuthal anisotropy harmonics v2 and v3 are compared across pp, pPb, and PbPb collisions, highlighting a consistent pattern in the high-multiplicity region that suggests implications for the understanding of the initial-state conditions in these collisions.
The findings invite further theoretical exploration into the dynamics of such small, dense systems. Future research could focus on refining hydrodynamic models or investigating alternative explanations involving initial-state fluctuations. Enhancing the precision of these experiments or extending them to even smaller systems could yield further insights into the nature of strongly interacting matter at extreme densities.
This paper demonstrates an important step forward in understanding the scope of collective behavior in particle physics, suggesting that our current models could benefit from revisions that incorporate these unexpected results from pp collisions. As the LHC continues its exploration at even higher energies, the prospect for further revelations remains substantial.