Measurement of the energy density as a function of pseudorapidity in proton-proton collisions at √s = 13 TeV

Abstract

A measurement of the energy density in proton–proton collisions at a centre-of-mass energy of \(\sqrt{s}=13\) \(\phantom{\rule{0.166667em}{0ex}}\text{TeV}\) 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 \(-\phantom{\rule{0.166667em}{0ex}}6.6<\eta <-\phantom{\rule{0.166667em}{0ex}}5.2\) and \(3.15<|\eta |<5.20\). 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 \(\sqrt{s}=0.9\) and \(7\phantom{\rule{0.166667em}{0ex}}\text{TeV}\) confirms the compatibility of the data with the hypothesis of limiting fragmentation.