Simulating QGP-like effects in pp collisions

Abstract

Our goal is to set the first step towards a microscopic model of Quark Gluon Plasma (QGP). QGP is a state of matter where quarks and gluons, which are normally bound inside hadrons, attain a quasi-freedom. Quarks and gluons are the fundamental constituents of Quantum Chromo-dynamics (QCD).

Our approach to this goal is to use simulations to try to recreate QGP-like effects observed experimentally in pp collisions. Specifically, we try to test whether we can qualitatively reproduce the multiplicity dependence found experimentally in the baryon over meson transverse momentum spectra. We hypothesize that we can do this by introducing color reconnection (CR) in a model called Pythia. The Pythia model uses simulations to describe the final state products from particle collisions.

We used Pythia 8.2 with the Monash tune. We varied three parameters; CR (on or off), the type of QCD used (hard or soft), and the center-of-mass energy (7 TeV or 13 TeV). For each combination of these parameters we simulated roughly $2*10^9$ events. We then focused on the transverse momentum spectra for various particle types and their ratios ($p/\pi$, $\Lambda/K^{0}_{s}$, and $\Lambda_{c}/D^{0}$).

In our results, we found that CR introduced a multiplicity dependence in the baryon over meson ratio transverse momentum spectra for light flavors. The effect qualitatively agreed with the effects observed experimentally in pp collisions. We were unable to reach a similar conclusion for charm flavor due to a lack of statistics.

We conclude that CR is a highly promising candidate for capturing QGP-like effects in simulations of pp collisions.