Measurement of the forward charged particle pseudorapidity density in pp collisions at $$\sqrt{s} = 8$$ s = 8  TeV using a displaced interaction point

Abstract

The pseudorapidity density of charged particles dN $$_{ ch }$$ /d $$\eta $$ is measured by the TOTEM experiment in proton–proton collisions at $$\sqrt{s} = 8$$ TeV within the range $$3.9<\eta <4.7$$ and $$-6.95<\eta <-6.9$$ . Data were collected in a low intensity LHC run with collisions occurring at a distance of 11.25 m from the nominal interaction point. The data sample is expected to include 96–97 % of the inelastic proton–proton interactions. The measurement reported here considers charged particles with $$p_T>0$$ MeV/c, produced in inelastic interactions with at least one charged particle in $$-7<\eta <-6$$ or $$3.7<\eta <4.8$$ . The dN $$_{ ch }$$ /d $$\eta $$ has been found to decrease with $$|\eta |$$ , from 5.11 $$\pm $$ 0.73 at $$\eta =3.95$$ to 1.81 $$\pm $$ 0.56 at $$\eta =-$$ 6.925. Several Monte Carlo generators are compared to the data and are found to be within the systematic uncertainty of the measurement.