Measurement of the underlying event activity at the LHC with $ \sqrt {s} = 7 $ TeV and comparison with $ \sqrt {s} = 0.9 $ TeV

Abstract

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.

Underlying Event measurements in pp collisions at $ \sqrt {s} = 0.9 $ and 7 TeV with the ALICE experiment at the LHC

“…The results of a constant fit in the range 4 < p T,LT < 10 GeV/c are reported in table 8. The measured scaling factor for a p T threshold of 0.5 GeV/c is in agreement with the observations of ATLAS [7,30] and CMS [31].…”

Measurement of the underlying event activity in pp collisions at $ \sqrt {s} = 0.9 $ and 7 TeV with the novel jet-area/median approach

“…centre-of-mass energies, emphasises the need for measurements of the UE at different energies [1][2][3][4][5][6]. Retuned models allow for more precise measurements of observables based on jets or relying on isolation cones, for example in diphoton events from QCD processes or decays of the Higgs boson.…”

“…a measure of the momentum transfer in the hard partonic scattering. Studies using this approach were performed at the Tevatron [1][2][3] and the Large Hadron Collider (LHC) [4][5][6].…”

“…Even though this analysis contains data taken at two different centre-of-mass energies, all event selection and trigger criteria are identical throughout to guarantee compatibility of the results and consistency with the conventional UE measurement [4].…”

“…The track selection of this analysis follows that of the conventional UE measurement as discussed in [4]. In detail, the following criteria are applied:…”