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Paper   IPM / Particles / 12014
School of Particles and Accelerator
  Title:   Measurement of the Underlying Event Activity at the LHC with sqrt(s) = 7 TeV and Comparison with sqrt(s) = 0.9 TeV
1.  Hessamadin Arfaei
2.  Hamed Bakhshiansohi
3.  Seyed Mohsen Etesami
4.  Ali Fahim
5.  Majid Hashemi
6.  Abideh Jafari
7.  Mohsen Khakzad
8.  A Mohammadi
9.  Mojtaba Mohammadi Najafabadi
10.  Saeid Paktinat Mehdiabadi
11.  Batool Safarzadeh
12.  Maryam Zeinali
  Status:   Published
  Journal: JHEP
  No.:  109
  Vol.:  1109
  Year:  2011
  Supported by:  IPM
A measurement of the underlying activity in scattering processes with a hard scale in the several GeV region is performed in proton-proton collisions at sqrt(s)= 0.9 and 7 TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity jhj < 2 and transverse momentum pT > 0.5 GeV/c is studied in the azimuthal region transverse to that of the leading set of charged particles forming a track-jet. A significant growth of the average multiplicity and scalar-pT sum of the particles in the transverse region is observed with increasing pT of the leading track-jet, followed by a much slower rise above a few GeV/c. For track-jet pT larger than a few GeV/c, the activity in the transverse region is approximately doubled with a centre-of-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as implemented in PYTHIA are compared to the data

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