A measurement is presented of the primary Lund jet plane (LJP) density in
inclusive jet production in proton-proton collisions. The analysis uses 138 fb−1
of data
collected by the CMS experiment at √
s = 13 TeV. The LJP, a representation of the phase
space of emissions inside jets, is constructed using iterative jet declustering. The transverse
momentum kT and the splitting angle ∆R of an emission relative to its emitter are measured
at each step of the jet declustering process. The average density of emissions as function
of ln(kT/GeV) and ln(R/∆R) is measured for jets with distance parameters R = 0.4 or 0.8,
transverse momentum pT > 700 GeV, and rapidity |y| < 1.7. The jet substructure is measured
using the charged-particle tracks of the jet. The measured distributions, unfolded to the
level of stable charged particles, are compared with theoretical predictions from simulations
and with perturbative quantum chromodynamics calculations. Due to the ability of the LJP
to factorize physical efects, these measurements can be used to improve diferent aspects
of the physics modeling in event generators.