First Measurement of the Underlying Event Activity at the LHC with $\sqrt{s} = 0.9$ TeV
Eur.Phys.J. C70 (2010) 555-572, 2010.
The collaboration

Abstract (data abstract)
CERN-LHC, Measurement of the properties of the underlying event activity for charged hadron production in proton-proton collisions at a centre-of-mass energy of 900 GeV. The charged hadrons are required to have PT > 0.5 GeV and pseudorapidity in the range -2 to 2 with the presence of a hard scale provided by the PT of the leading charged particle or of the leading track-jet to be at least 1 to 3 GeV. By requiring the azimuthal angle difference (DELTA(PHI)) between the direction, in the plane transverse to the beams, of the leading object and that of the charged hadron to be between 60 and 120 GeV, the transvese region is selected. Numerical values supplied by R Field.