Identified particle yield associated with a high-pT trigger particle at the LHC

Abstract

Identified particle production ratios are important observables, used to constrain models of particle production in heavy-ion collisions. Measurements of the inclusive particle ratio in central heavy-ion collisions showed an increase of the baryon-to-meson ratio compared to proton-proton collisions at intermediate pT, the so-called baryon anomaly. One possible explanation of the baryon anomaly is that partons from the thermalized deconfined QCD matter hadronize in a different way compared to hadrons produced in a vacuum jet. In this work we extend on previous measurements by measuring particle ratios in the yield associated with a high-pT trigger particle. These measurements can potentially further constrain the models of particle production since they are sensitive to the difference between particles from a jet and particles that are produced in the bulk. We start by developing a particle identification method that uses both the specific energy loss of a particle and the time of flight. From there, we present a method to identify the particle yield associated with a high-pT trigger particle. We then measure the proton-to-pion and kaon-to-pion ratio in the jet peak and background of the associated yield in central Pb-Pb, central p-Pb and pp collisions. The observation that these particle ratios are higher in the background compared to the jet peak suggests that there is a difference between the mechanism of hadron production in the the underlying event and the jet. Furthermore, our results show that the particle ratios in the jet peak depend on the size of the system.