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Measurement of the Cross Section of Four-Jet Events

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High Jet Multiplicity Physics at the LHC

Part of the book series: Springer Theses ((Springer Theses))

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Abstract

This chapter presents a measurement of the cross section of four-jet events produced in 8 TeV collisions. The opening sections contain all the studies performed to define the analysis strategy, including the trigger criteria, kinematic selection, and the variables used to study the cross section differentially across multiple regions of phase space. The following sections focus on some of the most important steps of the analysis procedure, namely the determination of the bin widths for each variable, the unfolding process, and the calculation of the uncertainties. Finally, the results are discussed and compared to a variety of theoretical predictions.

‘How can I have done that?’ she thought.

‘I must be growing small again.’ She got up and went to the table to measure herself by it.

Lewis Carroll, Alice’s Adventures in Wonderland

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Notes

  1. 1.

    See Sect. 2.5.4 for a more detailed summary of how jets are reconstructed and calibrated in ATLAS.

  2. 2.

    A high number of iterations was chosen to maximise the shape accuracy in the unfolding. Since this unfolded spectrum is only used as a reference to derive the reweighting function, it is seen to provide good agreement at reconstructed level, and does not get propagated through the test in any way, the number of iterations does not need to be optimised.

  3. 3.

    A kernel regression estimates the continuous distribution of a variable from a set of data points. The value of the distribution at each point is obtained from the weighted contributions of the data points; in this study, the weighting function—or kernel function—is a Gaussian.

  4. 4.

    Except for when the Jet Energy Resolution is evaluated. This is explained in the following subsection.

  5. 5.

    Effectively this means that 100 replicas of the upward- and downward-fluctuated spectra are independently unfolded.

  6. 6.

    \(\sigma \) was defined in the context of the shape uncertainty, in Sect. 4.6.3.

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Authors and Affiliations

  1. Memorial Sloan Kettering Cancer Center, New York, NY, USA

    Mireia Crispín Ortuzar

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Ortuzar, M.C. (2016). Measurement of the Cross Section of Four-Jet Events. In: High Jet Multiplicity Physics at the LHC. Springer Theses. Springer, Cham. https://doi.org/10.1007/978-3-319-43461-2_4

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