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

TL;DR

This paper reports the first measurement of charged particle density in the forward pseudorapidity region at 7 TeV pp collisions, extending previous studies and challenging existing Monte Carlo models.

Contribution

It provides the first measurement of dN_{ch}/deta in the forward region at 7 TeV, covering a previously unexplored pseudorapidity range and including a significant portion of inelastic processes.

Findings

dN_{ch}/deta decreases with |eta| from 3.84 to 2.38

None of the tested MC generators fully reproduce the data

Measurement covers over 99% of non-diffractive processes

Abstract

The TOTEM experiment has measured the charged particle pseudorapidity density dN_{ch}/deta 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}/deta 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.