Study of the underlying event at forward rapidity in pp collisions at sqrt(s) = 0.9, 2.76, and 7 TeV

S. Chatrchyan , M. Besançon (1) , S. Choudhury (1) , F. Couderc (1) , M. Dejardin (1) , D. Denegri (1) , B. Fabbro (1) , J.L. Faure (1) , F. Ferri (1) , S. Ganjour (1) , A. Givernaud (1) , P. Gras (1) , G. Hamel de Monchenault (1) , P. Jarry (1) , E. Locci (1) , J. Malcles (1) , L. Millischer (1) , A. Nayak (1) , J. Rander (1) , A. Rosowsky (1) , M. Titov (1) , S. Baffioni (2) , F. Beaudette (2) , L. Benhabib (2) , L. Bianchini (2) , M. Bluj (2) , Pierre Busson (2) , C. Charlot (2) , N. Daci (2) , T. Dahms (2) , M. Dalchenko (2) , L. Dobrzynski (2) , A. Florent (2) , R. Granier de Cassagnac (2) , M. Haguenauer (2) , P. Mine (2) , C. Mironov (2) , I.N. Naranjo (2) , M. Nguyen (2) , C. Ochando (2) , P. Paganini (2) , D. Sabes (2) , R. Salerno (2) , Y. Sirois (2) , C. Veelken (2) , A. Zabi (2) , J.-L. Agram (3) , J. Andrea (3) , D. Bloch (3) , D. Bodin (3) , J.-M. Brom (3) , E.C. Chabert (3) , C. Collard (3) , E. Conte (3) , F. Drouhin (3) , J.-C. Fontaine (3) , D. Gele (3) , U. Goerlach (3) , P. Juillot (3) , A.-C. Le Bihan (3) , P. van Hove (3) , S. Beauceron (4) , N. Beaupere (4) , O. Bondu (4) , G. Boudoul (4) , S. Brochet (4) , J. Chasserat (4) , R. Chierici (4) , D. Contardo (4) , P. Depasse (4) , H. El Mamouni (4) , J. Fay (4) , S. Gascon (4) , M. Gouzevitch (4) , B. Ille (4) , T. Kurca (4) , M. Lethuillier (4) , L. Mirabito (4) , S. Perries (4) , L. Sgandurra (4) , V. Sordini (4) , Y. Tschudi (4) , P. Verdier (4) , S. Viret (4)

1 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
2 LLR - Laboratoire Leprince-Ringuet
3 DRS-IPHC - Département Recherches Subatomiques
4 IPNL - Institut de Physique Nucléaire de Lyon

The underlying event activity in proton-proton collisions at forward pseudorapidity (-6.6 < eta < -5.2) is studied with the CMS detector at the LHC, using a novel observable: the ratio of the forward energy density, dE/d(eta), for events with a charged-particle jet produced at central pseudorapidity (abs(eta[jet]) < 2) to the forward energy density for inclusive events. This forward energy density ratio is measured as a function of the central jet transverse momentum, pt, at three different pp centre-of-mass energies (sqrt(s) = 0.9, 2.76, and 7 TeV). In addition, the sqrt(s) evolution of the forward energy density is studied in inclusive events and in events with a central jet. The results are compared to those of Monte Carlo event generators for pp collisions and are discussed in terms of the underlying event. Whereas the dependence of the forward energy density ratio on jet pt at each sqrt(s) separately can be well reproduced by some models, all models fail to simultaneously describe the increase of the forward energy density with sqrt(s) in both inclusive events and in events with a central jet.

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

S. Chatrchyan, M. Besançon, S. Choudhury, F. Couderc, M. Dejardin, et al.. Study of the underlying event at forward rapidity in pp collisions at sqrt(s) = 0.9, 2.76, and 7 TeV. Journal of High Energy Physics, 2013, 04(2013), pp.072. ⟨10.1007/JHEP04(2013)072⟩. ⟨in2p3-00787343⟩