Study of event shape in pp collisions at LHC energies using the PYTHIA model

Abstract

Recent experimental results from the analysis of pp collisions at the LHC have sparked much interest since they resemble the ones reported in heavy-ion collisions. The latter are consistent with the creation of a hot and dense coloured matter, the quark-gluon plasma (QGP). These results pose an intriguing question related to their physics origin and force people to look in pp collisions in more detail. In this report, we analyse simulated data of pp collisions at √ s = 7 TeV for two sets of Monte-Carlo generated collision data using PYTHIA. In particular we focus on different shapes (i.e. jetty vs spherical events) of pp collisions in an attempt to distinguish between phenomena that can be described by QCD or by phenomenological approaches. It is found that high multiplicity events have preferentially high sphericity. Moreover, high pT events are jetty, and low pT events are spherical. In one of the two datasets colour reconnection (CR) is turned on, and in the other off. This mechanism is one of the phenomenological principles that can explain the QGP-like behaviour in pp collisions. Although only a small difference is found, CR could explain a rise in pT over multiplicity.