Probing collective effects in hadronisation with the extremes of the underlying event

T. Martin, P. Skands, S. Farrington

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We define a new set of observables to probe the structure of the underlying event in hadron collisions. We use the conventional definition of the “transverse region” in jet events and, for a fixed window in jet p, propose to measure several discriminating quantities as a function of the level of activity in the transverse region. The measurement of these observables in LHC data would reveal whether, e.g., the properties of “low-UE” events are compatible with equivalent measurements in e+e-collisions (jet universality), and whether the scaling behaviour towards “high-UE” events exhibits properties of non-trivial soft-QCD dynamics, such as colour reconnections or other collective phenomena. We illustrate at s=13TeV that significant discriminatory power is obtained in comparisons between MC models with varying treatments of collective effects, including Pythia 8, epos, and Dipsy.

Original languageEnglish
Article number299
Number of pages12
JournalEuropean Physical Journal C
Issue number5
Publication statusPublished - 1 May 2016
  • The extremes of the underlying event

    Martin, T., Skands, P. & Farrington, S., 2016, 38th International Conference on High Energy Physics, ICHEP 2016: Chicago; United States; 3 August 2016 through 10 August 2016; Code 128556. Vol. Part F128556. 4 p. 606

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