Abstract
This paper presents a measurement of the underlying event activity in proton-proton collisions at a center-of-mass energy of 13 TeV, performed using inclusive Z boson production events collected with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 2.1 fb−1. The underlying event activity is quantified in terms of the charged particle multiplicity, as well as of the scalar sum of the charged particles’ transverse momenta in different topological regions defined with respect to the Z boson direction. The distributions are unfolded to the stable particle level and compared with predictions from various Monte Carlo event generators, as well as with similar CDF and CMS measurements at center-of-mass energies of 1.96 and 7 TeV respectively.
Highlights
Of universality of the underlying MPI dynamics
This paper presents a measurement of the underlying event activity in protonproton collisions at a center-of-mass energy of 13 TeV, performed using inclusive Z boson production events collected with the CMS experiment at the LHC
Events with a harder scale are expected to correspond, on average, to proton-proton interactions with a smaller impact parameter and with more MPI [10]. Such increased underlying event (UE) activity is observed to plateau at high energy scales, which indicates that the smallest impact parameters have been reached and maximum matter overlap in the pp collision [11]
Summary
Events with a harder scale are expected to correspond, on average, to proton-proton interactions with a smaller impact parameter and with more MPI [10]. Such increased UE activity is observed to plateau at high energy scales, which indicates that the smallest impact parameters have been reached and maximum matter overlap in the pp collision [11]. The properties of the UE are measured as a function of conventional observables related to the impact parameter of the pp collision, such as the number of charged particles and the scalar sum of their pT. Data were collected with the CMS detector in 2015 when the average number of inelastic collisions per bunch crossing (pileup) was about 20
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