Measurement of the forward charged particle pseudorapidity density in pp collisions at s=8 TeV using a displaced interaction point: TOTEM Collaboration

The pseudorapidity density of charged particles dN(ch)/d(eta) is measured by the TOTEM experiment in proton-proton collisions at root 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 vertical bar eta vertical bar, from 5.11 +/- 0.73 at eta = 3.95 to 1.81 +/- 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.