Underlying Event measurements in pp collisions at sqrt(s) = 0.9 and 7 TeV with the ALICE experiment at the LHC

B. Abelev , N. Arbor (1) , G. Conesa Balbastre (1) , J. Faivre (1) , C. Furget (1) , R. Guernane (1) , S. Kox (1) , Y. Mao (1) , J.S. Real (1) , R. Vernet (2) , I. Belikov (3) , J.P. Coffin (3) , Z. Conesa del Valle (3) , B. Hippolyte (3) , S. Jangal (3) , C. Kuhn (3) , A. Maire (3) , A. Michalon (3) , C. Roy (3) , X. Sanchez Castro (3) , S. Senyukov (3) , R. Wan (3) , Laurent Aphecetche (4) , Guillaume Batigne (4) , M. Bregant (4) , H. Delagrange (4) , O. Driga (4) , Magali Estienne (4) , Marie Germain (4) , A. Lardeux (4) , F. Lefèvre (4) , M. Lenhardt (4) , L. Luquin (4) , Gines Martinez Garcia (4) , A. Mas (4) , A. Matyja (4) , Philippe Pillot (4) , Y. Schutz (4) , Alexandre Shabetai (4) , Diego Stocco (4) , C. Cheshkov (5) , B. Cheynis (5) , L. Ducroux (5) , J.-Y. Grossiord (5) , Maxime Guilbaud (5) , L. Massacrier (5) , R. Tieulent (5) , A. Uras (5) , Y. Zoccarato (5) , Sang Un Ahn (6) , Y.W. Baek (6) , A. Baldit (6) , V. Barret (6) , N. Bastid (6) , P. Crochet (6) , P. Dupieux (6) , R. Ichou (6) , X. Lopez (6) , F. Manso (6) , M. Marchisone (6) , S. Porteboeuf-Houssais (6) , P. Rosnet (6) , B. Vulpescu (6) , X. Zhang (6)

1 LPSC - Laboratoire de Physique Subatomique et de Cosmologie
2 CC-IN2P3 - Centre de Calcul de l'IN2P3
3 DRS-IPHC - Département Recherches Subatomiques
4 SUBATECH - Laboratoire SUBATECH Nantes
5 ALICE
6 LPC - Laboratoire de Physique Corpusculaire - Clermont-Ferrand

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%.

Domaines: Physique des Hautes Energies - Expérience [hep-ex]

B. Abelev, N. Arbor, G. Conesa Balbastre, J. Faivre, C. Furget, et al.. Underlying Event measurements in pp collisions at sqrt(s) = 0.9 and 7 TeV with the ALICE experiment at the LHC. Journal of High Energy Physics, 2012, 07(2012), pp.116. ⟨10.1007/JHEP07(2012)116⟩. ⟨in2p3-00650724⟩