Spectra of identified hadrons in Pb-Pb collisions at 2.76 TeV at the CERN Large Hadron Collider

Abstract

The transverse-momentum distributions of identified hadrons produced in Pb-Pb collisions at the Large Hadron Collider (LHC) are studied in the low and intermediate range for ${p}_{T}<5$ GeV/$c$. All four spectra ($\ensuremath{\pi},K,p,\ensuremath{\Lambda}$) can be well reproduced in the recombination model based on a common thermal parton distribution of light and strange quarks and on shower partons emitted in hard and semihard jets. Two essential parameters are adjusted to fit the data, one being the inverse slope of the thermal distribution and the other revealing the degree of momentum degradation in the medium. Various combinations of thermal and shower-parton components are calculated, showing the dominance of minijets. The effect of minijets is to produce harder baryons than mesons, resulting in their ratio to peak at around ${p}_{T}\ensuremath{\sim}3$ GeV/$c$. A substantial portion of the jet energy is found to be lost to the dense medium before the partons emerge at the surface to undergo hadronization by recombination.