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Published April 2013 | Submitted + Published
Journal Article Open

Study of the underlying event at forward rapidity in pp collisions at √s = 0.9, 2.76, and TeV


The underlying event activity in proton-proton collisions at forward pseudo-rapidity (−6.6 < η < −5.2) is studied with the CMS detector at the LHC, using a novel observable: the ratio of the forward energy density, dE/dη, for events with a charged-particle jet produced at central pseudorapidity (|η^(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, p_T, at three different pp centre-of-mass energies ( s√=0.9 , 2.76, and 7 TeV). In addition, the 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 p_T at each s√ separately can be well reproduced by some models, all models fail to simultaneously describe the increase of the forward energy density with s√ in both inclusive events and in events with a central jet.

Additional Information

© 2013 CERN for the benefit of the CMS collaboration. Published for SISSA by Springer. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited. Received: February 11, 2013. Accepted: March 21, 2013. Published: April 11, 2013. We would like to thank Leif Lönnblad for making the DIPSY predictions available to the CMS collaboration. We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC and thank the technical and administrative staffs at CERN and at other CMS institutes for their contributions to the success of the CMS effort. In addition, we gratefully acknowledge the computing centres and personnel of the Worldwide LHC Computing Grid for delivering so effectively the computing infrastructure essential to our analyses. Finally, we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMWF and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MEYS (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09 and ERDF (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 (Republic of Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MON, RosAtom, RAS and RFBR (Russia); MSTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); ThEPCenter, IPST and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU (Ukraine); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the A.G. Leventis Foundation, the Helmholtz Association, the Russian Foundation for Basic Research, the Russian Federation Presidential Grants N1456.2008.2, N4142.2010.2 and N3920.2012.2, the Russian Ministry of Education and Science, and the Belgian Federal Science Policy Office.

Attached Files

Published - art_10.1007_JHEP04_2013_072.pdf

Submitted - 1302.2394v2.pdf


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