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Journal of High Energy Physics 07(2012) (2012) 116
Underlying Event measurements in pp collisions at sqrt(s) = 0.9 and 7 TeV with the ALICE experiment at the LHC
B. Abelev, N. Arbor1, G. Conesa Balbastre1, J. Faivre1, C. Furget1, R. Guernane1, S. Kox1, Y. Mao1, J.S. Real1, R. Vernet2, I. Belikov3, J.P. Coffin3, Z. Conesa Del Valle3, B. Hippolyte3, S. Jangal3, C. Kuhn3, A. Maire3, A. Michalon3, C. Roy3, X. Sanchez Castro3, S. Senyukov3, R. Wan3, L. Aphecetche4, Guillaume Batigne4, M. Bregant4, H. Delagrange4, O. Driga4, M. Estienne4, M. Germain4, A. Lardeux4, F. Lefèvre4, M. Lenhardt4, L. Luquin4, G. Martınez Garcıa4, A. Mas4, A. Matyja4, P. Pillot4, Y. Schutz4, A. Shabetai4, D. Stocco4, C. Cheshkov5, B. Cheynis5, L. Ducroux5, J.-Y. Grossiord5, M. Guilbaud5, L. Massacrier5, R. Tieulent5, A. Uras5, Y. Zoccarato5, Sang Un Ahn6, Y. .W. Baek6, A. Baldit6, V. Barret6, N. Bastid6, P. Crochet6, P. Dupieux6, R. Ichou6, X. Lopez6, F. Manso6, M. Marchisone6, S. Porteboeuf-Houssais6, P. Rosnet6, B. Vulpescu6, X. Zhang6
ALICE Collaboration(s)

We present measurements of Underlying Event observables in pp collisions at sqrt(s) = 0.9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum pT,LT in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different pT thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track pT threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed pT in the Transverse region by about 10-30%.
1 :  LPSC - Laboratoire de Physique Subatomique et de Cosmologie
2 :  CC IN2P3 - Centre de Calcul de l'inst. national de phy. nucléaire et de phy. des particules
3 :  DRS-IPHC - Département Recherches Subatomiques
4 :  SUBATECH - Laboratoire SUBATECH Nantes
5 :  IPNL - Institut de Physique Nucléaire de Lyon
6 :  LPC - Laboratoire de Physique Corpusculaire [Clermont-Ferrand]
Laboratoire de Physique Corpusculaire
Physique/Physique des Hautes Energies - Expérience
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