, Volume 70, Issue 3, pp 555-572,
Open Access This content is freely available online to anyone, anywhere at any time.
Date: 06 Nov 2010

First measurement of the underlying event activity at the LHC with  \(\sqrt{s} = 0.9\)  TeV


A measurement of the underlying activity in scattering processes with p T scale in the GeV region is performed in proton–proton collisions at \(\sqrt{s} = 0.9\)  TeV, using data collected by the CMS experiment at the LHC. Charged particle production is studied with reference to the direction of a leading object, either a charged particle or a set of charged particles forming a jet. Predictions of several QCD-inspired models as implemented in PYTHIA are compared, after full detector simulation, to the data. The models generally predict too little production of charged particles with pseudorapidity |η|<2, p T >0.5 GeV/c, and azimuthal direction transverse to that of the leading object.