Measurement of the underlying event activity at the LHC with √s = 7 TeV and comparison with √s = 0.9 TeV

Creators: Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Gataullin, M.; Ma, Y.; Mott, A.; Newman, H. B.; Rogan, C.; Shin, K.; Timciuc, V.; Traczyk, P.; Veverka, J.; Wilkinson, R.; Yang, Y.; Zhu, R. Y.; Dubinin, M.; Spiropulu, M.; CMS Collaboration

Abstract

A measurement of the underlying activity in events with a jet of transverse momentum in the several GeV region is performed in proton-proton collisions at √s = 0.9 and 7 TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity |η|<2 and transverse momentum p_T > 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 signicant growth of the average multiplicity and scalar-p_T sum of the particles in the transverse region is observed with increasing p_T of the leading trackjet, followed by a much slower rise above a few GeV/c. For track-jet p_T 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.

Additional Information

© 2011 CERN, for the benefit of the CMS collaboration. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. Received: July 1, 2011; accepted: August 31, 2011; published: September 23, 2011. We thank Mark Strikman (Penn State University) and Torbjorn Sjöstrand (Lund University) for useful discussions and for assistance in simulating theoretical models. We wish to congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC machine. We thank the technical and administrative staff at CERN and other CMS institutes, and acknowledge support from:FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy of Sciences and NICPB (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pakistan); SCSR (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie programme and the European Research Council (European Union); the Leventis Foundation; the A. P. Sloan Foundation; the Alexander von Humboldt Foundation; the Associazione per lo Sviluppo Scientico e Tecnologico del Piemonte (Italy); the Belgian Federal Science Policy Offce; the Fonds pour la Formation à la Recherche dans l'Industrie et dans l'Agriculture (FRIA-Belgium); and the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium).

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