Eventwise mean-ptfluctuations versus minimum-bias jets (minijets) at energies available at the CERN Large Hadron Collider

Abstract

Fluctuation measurements of eventwise mean transverse momentum $\ensuremath{\langle}{p}_{t}\ensuremath{\rangle}$ for $p\text{\ensuremath{-}}p$ and Pb-Pb collisions at the CERN Large Hadron Collider (LHC) have been reported recently. In that study it was concluded that the strength of ``nonstatistical'' $\ensuremath{\langle}{p}_{t}\ensuremath{\rangle}$ fluctuations decreases with increasing particle multiplicity ${n}_{\text{ch}}$ (or $A\text{\ensuremath{-}}A$ centrality) and is nearly independent of collision energy over a large interval. Among several potential mechanisms for those trends the onset of thermalization and collectivity are mentioned. The LHC analysis employed one fluctuation measure selected from several possibilities. An alternative fluctuation measure reveals a strong increase of ${p}_{t}$ fluctuations with ${n}_{ch}$ (or $A\text{\ensuremath{-}}A$ centrality) and collision energy, consistent with previous measurements at the BNL Relativistic Heavy Ion Collider (RHIC). The ${p}_{t}$ fluctuation data for LHC $p\text{\ensuremath{-}}p$ collisions can be described accurately by a two-component $(\mathrm{soft}+\mathrm{hard})$ model (TCM) in which the hard component represents dijet production. The data for Pb-Pb collisions are described accurately by a TCM reference for more-peripheral collisions (suggesting transparent collisions), but the data deviate quantitatively from the reference for more-central collisions, suggesting a modification of jet formation. Overall fluctuation data trends suggest that minimum-bias jets (minijets) dominate ${p}_{t}$ fluctuations at both the LHC and the RHIC.