TAILIEUCHUNG - Measurement of the underlying event in the Drell–Yan process in proton–proton collisions at √ s =7 TeV

A measurement of the underlying event (UE) activity in proton–proton collisions at a center-of-mass energy of 7 TeV is performed using Drell–Yan events in a data sample corresponding to an integrated luminosity of fb−1, collected by the CMS experiment at the LHC. The activity measured in the muonic final state (qq → μ + μ −) is corrected to the particle level and compared with the predictions of various Monte Carlo generators and hadronization models. The dependence of the UE activity on the dimuon invariant mass is well described by PYTHIA and HERWIG++ tunes derived from the leading jet/track approach, illustrating the universality of the UE activity. The UE activity is observed to be. | The European Physical Journal c Eur. Phys. J. C 2012 72 2080 DOI epjc s10052-012-2080-4 Regular Article - Experimental Physics Measurement of the underlying event in the Drell-Yan process in proton-proton collisions at ựs 7 TeV The CMS Collaboration CERN Geneva Switzerland Received 6 April 2012 Revised 3 July 2012 Published online 20 September 2012 CERN for the benefit of the CMS collaboration 2012. This article is published with open access at Abstract A measurement of the underlying event UE activity in proton-proton collisions at a center-of-mass energy of 7 TeV is performed using Drell-Yan events in a data sample corresponding to an integrated luminosity of fb-1 collected by the CMS experiment at the LHC. The activity measured in the muonic final state qq ịẪ is corrected to the particle level and compared with the predictions of various Monte Carlo generators and hadronization models. The dependence of the UE activity on the dimuon invariant mass is well described by PYTHIA and HERWIG tunes derived from the leading jet track approach illustrating the universality of the UE activity. The UE activity is observed to be independent of the dimuon invariant mass in the region above 40 GeV c2 while a slow increase is observed with increasing transverse momentum of the dimuon system. The dependence of the UE activity on the transverse momentum of the dimuon system is accurately described by MADGRAPH which simulates multiple hard emissions. 1 Introduction In hadron-hadron scattering the underlying event UE is defined as any hadronic activity that cannot be attributed to the particles originating from the hard scattering which is characterized by a large momentum transfer or to the hadronization of initial- and final-state radiation. The UE activity is thus due to the hadronization of partonic constituents not involved in the hard scattering that have undergone multiple-parton interactions MPIs and to the hadronization of beam remnants that .

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