A measurement of the energy density in proton–
proton collisions at a centre-of-mass energy of √s = 13 TeV
is presented. The data have been recorded with the CMS
experiment at the LHC during low luminosity operations in
2015. The energy density is studied as a function of pseudorapidity in the ranges − 6.6 <η< − 5.2 and 3.15 < |η| <
5.20. The results are compared with the predictions of several
models. All the models considered suggest a different shape
of the pseudorapidity dependence compared to that observed
in the data. A comparison with LHC proton–proton collision
data at √s = 0.9 and 7 TeV confirms the compatibility of
the data with the hypothesis of limiting fragmentation
