Abstract
The study of global event shape variables can provide sensitive tests of predictions for multijet production in proton-proton collisions. This paper presents a study of several event shape variables calculated using jet four momenta in proton-proton collisions at a centre-of-mass energy of 13 TeV and uses data recorded with the CMS detector at the LHC corresponding to an integrated luminosity of 2.2 fb−1. After correcting for detector effects, the resulting distributions are compared with several theoretical predictions. The agreement generally improves as the energy, represented by the average transverse momentum of the two leading jets, increases.
Highlights
This paper presents a study of several event shape variables calculated using jet four momenta in proton-proton collisions at a centre-of-mass energy of 13 TeV and uses data recorded with the CMS detector at the LHC corresponding to an integrated luminosity of 2.2 fb−1
The modelling of initial-state radiation (ISR), final-state radiation (FSR) of gluons, and multiple parton interaction (MPI) in pythia8 CUETP8M1 is tested by studying each aspect individually, via the comparison of simulated ESV distributions with data, as shown in figure 2
This study shows that the effect of disabling ISR results in a very large shift of the ESVs to lower values, i.e., reducing the spherical nature of the multijet events
Summary
The four ESVs studied in this analysis are defined using the four-momenta of hadronic jets. Total jet broadening: for each event, the transverse thrust axis is used to divide the event into upper (U) and lower (L) regions. Total jet mass: the normalized squared invariant mass of the jets in the U and L regions of the event is defined by ρX. Total transverse jet mass: the quantity corresponding to ρTot in the transverse plane, the total transverse jet mass (ρTTot), is calculated using pT,i of jets. These four ESVs probe different aspects of QCD [2] and are designed to have higher values for multijet, spherical events and lower values for back-to-back dijet events. While τ⊥ is sensitive to the hard-scattering process, the jet masses and jet broadening depend more on the nonperturbative aspects of QCD, responsible for hadronisation process
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