/ hep-ex CMS-FSQ-12-022

Jet and underlying event properties as a function of particle multiplicity in proton-proton collisions at $\sqrt{s}$ = 7 TeV

Pages: 41

Abstract: Characteristics of multi-particle production in proton-proton collisions at $\sqrt{s}$ = 7 TeV are studied as a function of the charged-particle multiplicity, $N_{ch}$. The produced particles are separated into two classes: those belonging to jets and those belonging to the underlying event. Charged particles are measured with pseudorapidity abs(eta) < 2.4 and transverse momentum $p_T$ > 0.25 GeV. Jets are reconstructed from charged-particles only and required to have $p_T$ > 5 GeV. The distributions of jet $p_T$, average $p_T$ of charged particles belonging to the underlying event or to jets, jet rates, and jet shapes are presented as functions of $N_{ch}$ and compared to the predictions of the PYTHIA and HERWIG event generators. Predictions without multi-parton interactions fail completely to describe the $N_{ch}$-dependence observed in the data. For increasing $N_{ch}$, PYTHIA systematically predicts higher jet rates and harder $p_T$ spectra than seen in the data, whereas HERWIG shows the opposite trends. At the highest multiplicity, the data--model agreement is worse for most observables, indicating the need for further tuning and/or new model ingredients.

Note: Submitted to Eur. Phys. J. C

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