Measurement of the forward charged particle pseudorapidity density in pp collisions at $\sqrt{s}$ = 7 TeV with the TOTEM experiment

The TOTEM experiment has measured the charged particle pseudorapidity density dN$_{ch}$/d$\eta$ in pp collisions at $\sqrt{s}$ = 7 TeV for 5.3<|$\eta$|<6.4 in events with at least one charged particle with transverse momentum above 40 MeV/c in this pseudorapidity range. This extends the analogous measurement performed by the other LHC experiments to the previously unexplored forward $\eta$ region. The measurement refers to more than 99% of non-diffractive processes and to single and double diffractive processes with diffractive masses above ~3.4 GeV/c$^2$, corresponding to about 95% of the total inelastic cross-section. The dN$_{ch}$/d$\eta$ has been found to decrease with |$\eta$|, from 3.84 $\pm$ 0.01(stat) $\pm$ 0.37(syst) at |$\eta$| = 5.375 to 2.38 $\pm$ 0.01(stat) $\pm$ 0.21(syst) at |$\eta$| = 6.375. Several MC generators have been compared to data; none of them has been found to fully describe the measurement.