Measurement of the Underlying Event Activity at the LHC with sqrt(s)= 7 TeV and Comparison with sqrt(s) = 0.9 TeV

S. Chatrchyan , D. Sillou (1) , M. Besancon (2) , S. Choudhury (2) , M. Dejardin (2) , D. Denegri (2) , B. Fabbro (2) , J.L. Faure (2) , F. Ferri (2) , S. Ganjour (2) , F.X. Gentit (2) , A. Givernaud (2) , P. Gras (2) , G. Hamel de Monchenault (2) , P. Jarry (2) , E. Locci (2) , J. Malcles (2) , M. Marionneau (2) , L. Millischer (2) , J. Rander (2) , A. Rosowsky (2) , I. Shreyber (2) , M. Titov (2) , P. Verrecchia (2) , S. Baffioni (3) , F. Beaudette (3) , L. Benhabib (3) , L. Bianchini (3) , M. Bluj (3) , C. Broutin (3) , Pierre Busson (3) , C. Charlot (3) , T. Dahms (3) , L. Dobrzynski (3) , S. Elgammal (3) , R. Granier de Cassagnac (3) , M. Haguenauer (3) , P. Mine (3) , C. Mironov (3) , C. Ochando (3) , P. Paganini (3) , D. Sabes (3) , R. Salerno (3) , Y. Sirois (3) , C. Thiebaux (3) , B. Wyslouch (3) , A. Zabi (3) , J.-L. Agram (4) , J. Andrea (4) , D. Bloch (4) , D. Bodin (4) , J.-M. Brom (4) , M. Cardaci (4) , E.C. Chabert (4) , C. Collard (4) , E. Conte (4) , F. Drouhin (4) , C. Ferro (4) , J.-C. Fontaine (4) , D. Gele (4) , U. Goerlach (4) , S. Greder (4) , P. Juillot (4) , M. Karim (4) , A.-C. Le Bihan (4) , Y. Mikami (4) , P. van Hove (4) , F. Fassi (5) , D. Mercier (5) , C. Baty (6) , S. Beauceron (6) , N. Beaupere (6) , M. Bedjidian (6) , O. Bondu (6) , G. Boudoul (6) , D. Boumediene (6) , H. Brun (6) , J. Chasserat (6) , R. Chierici (6) , D. Contardo (6) , P. Depasse (6) , H. El Mamouni (7) , J. Fay (6) , S. Gascon (6) , B. Ille (6) , T. Kurca (6) , T. Le Grand (6) , M. Lethuillier (6) , L. Mirabito (6) , S. Perries (6) , V. Sordini (6) , S. Tosi (6) , Y. Tschudi (6) , P. Verdier (6)

1 LAPP - Laboratoire d'Annecy de Physique des Particules
2 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
3 LLR - Laboratoire Leprince-Ringuet
4 IPHC - Institut Pluridisciplinaire Hubert Curien
5 CC-IN2P3 - Centre de Calcul de l'IN2P3
6 IPNL - Institut de Physique Nucléaire de Lyon
7 CMS

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 |eta| < 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.

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

S. Chatrchyan, D. Sillou, M. Besancon, S. Choudhury, M. Dejardin, et al.. Measurement of the Underlying Event Activity at the LHC with sqrt(s)= 7 TeV and Comparison with sqrt(s) = 0.9 TeV. Journal of High Energy Physics, 2011, 9, pp.109. ⟨10.1007/JHEP09(2011)109⟩. ⟨in2p3-00605964⟩