Measurement of the energy density as a function of pseudorapidity in proton–proton collisions at $$\sqrt{s} =13\,\text {TeV} $$ s = 13 TeV

Abstract

Abstract A measurement of the energy density in proton–proton collisions at a centre-of-mass energy of

$$\sqrt{s} =13$$

s

= 13

$$\,\text {TeV}$$

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

$$-\,6.6<\eta <-\,5.2$$

-

6.6 < η < -

5.2

and

$$3.15<|\eta |<5.20$$

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

$$\sqrt{s} =0.9$$

s

= 0.9

and

$$7\,\text {TeV} $$

7

TeV

confirms the compatibility of the data with the hypothesis of limiting fragmentation.