Event-wise mean-$\bf p_t$ fluctuations vs minimum-bias jets (minijets) at the LHC

TL;DR

This paper compares different fluctuation measures of event-wise mean transverse momentum at the LHC, revealing that minijets significantly influence $p_t$ fluctuations across collision types and energies, challenging previous interpretations of thermalization effects.

Contribution

It introduces an alternative fluctuation measure that shows a strong increase in $p_t$ fluctuations with multiplicity and energy, and demonstrates the dominance of minijets in these fluctuations at LHC and RHIC.

Findings

An alternative fluctuation measure reveals increased $p_t$ fluctuations with multiplicity and energy.

A two-component model accurately describes $p_t$ fluctuations in p-p and peripheral Pb-Pb collisions.

Deviations in central Pb-Pb collisions suggest modifications in jet formation.

Abstract

Fluctuation measurements of event-wise mean transverse momentum $\langle p_t \rangle$ for p-p and Pb-Pb collisions at the large hadron collider (LHC) have been reported recently. In that study it was concluded that the strength of "nonstatistical" $\langle p_t \rangle$ fluctuations decreases with increasing particle multiplicity $n_{ch}$ (or A-A centrality) and is nearly independent of collision energy over a large interval. Among several potential mechanisms for those trends onset of thermalization and collectivity are mentioned. The LHC analysis employed one fluctuation measure selected from several possibilities. An alternative fluctuation measure reveals strong increase of $p_t$ fluctuations with $n_{ch}$ (or A-A centrality) and collision energy, consistent with previous measurements at the relativistic heavy ion collider (RHIC). The $p_t$ fluctuation data for LHC p-p collisions can be described accurately by a two-component (soft+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 modification of jet formation. Overall fluctuation data trends suggest that minimum-bias jets (minijets) dominate $p_t$ fluctuations at both the LHC and RHIC.