Ensemble mean ${\mathbf{p}}_{\mathbf{t}}$ vs charged-hadron multiplicities in high energy nuclear collisions

Abstract

Measurements of event-ensemble mean transverse momentum $⟨p_t⟩$ vs charged-hadron multiplicity $n_{ch}$ for $p_t$ spectra from 5 TeV p-Pb and 2.76 TeV Pb-Pb collisions and from p-p collisions for several energies have been reported recently. While in all cases $⟨p_t⟩$ increases monotonically with $n_{ch}$ the rate of increase is very different from system to system. Comparisons with several theory Monte Carlos reveal substantial disagreements and lead to considerable uncertainty on how to interpret the $⟨p_t⟩$ data. In the present study we develop a two-component (soft+hard) model (TCM) of $p_t$ production in high energy nuclear collisions and apply it to the $⟨p_t⟩$ data. The soft component is assumed to be a universal feature of high energy collisions independent of A-B system or energy. The hard-component model is based on the observation that dijet production in p-p collisions does not satisfy the eikonal approximation but does so in A-A collisions. Hard-component properties are determined from previous measurements of hadron spectrum hard components, jet spectra and fragmentation functions. The TCM describes the p-p and Pb-Pb $⟨p_t⟩$ data accurately, within data uncertainties, and the p-Pb data appear to transition smoothly from p-p to A-A $n_{ch}$ trends.

arXiv comment11 pages, 8 figures

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• Mini-jet Clustering Algorithm Using Transverse-momentum Seeds in High-energy Nuclear Collisions
• $\mathbf{p}$-$\mathbf{p}$ minimum-bias dijets and nonjet quadrupole in relation to conjectured collectivity (flows) in high-energy nuclear collisions