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Measurement of the underlying event activity at the LHC with √ s = 7 TeV and comparison with √ s = 0.9 TeVThe CMS collaboration E-mail: cms-publication-committee-chair@cern.chAbstract: 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 significant 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 centreof-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as implemented in pythia are compared to the data.

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The mass of the top quark is measured using a sample of events collected by the CMS detector using proton-proton collisions at at the CERN LHC. Events are selected with one isolated muon or electron and at least four jets from data corresponding to an integrated luminosity of 35.9 . For each event the mass is reconstructed from a kinematic fit of the decay products to a hypothesis. Using the ideogram method, the top quark mass is determined simultaneously with an overall jet energy scale factor (JSF), constrained by the mass of the W boson in decays. The measurement is calibrated on samples simulated at next-to-leading order matched to a leading-order parton shower. The top quark mass is found to be . The dependence of this result on the kinematic properties of the event is studied and compared to predictions of different models of production, and no indications of a bias in the measurements are observed.