Inelastic $pp$ cross section at 7 TeV

A new method to measure the inelastic pp cross section has been developed based on the assumption that pile-up events are randomly distributed according to a Poisson probability. This method relies only on the accurate knowledge of the CMS tracking system and it does not depend upon a specific Monte Carlo simulation. The value of the cross section for events with at least 2 charged particles with $|\eta|<2.4$ and $p_{\perp}~>~200 $ MeV is determined to be $ \sigma_{2-trks}(pp) {\rm =~58.7~\pm~2.0~(Syst)~\pm~2.4~(Lum)~mb} $. Using model-dependent extrapolations, the value for the total inelastic $pp$ cross section is determined to be $ \sigma_{inel}(pp) {\rm =~68.0~\pm~2.0~(Syst)~\pm~2.4~(Lum)~\pm~4~(Ext.)~mb} $. %In terms of the variable $\xi = M_x^2/s$, this measurement covers the interval $ \xi_{eq} > 6 \cdot 10^{-5}$.