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Abstract
A measurement of event-shape variables in proton-proton collisions at large momentum transfer is presented using data collected at sqrt{s} = 13 TeV with the ATLAS detector at the Large Hadron Collider. Six event-shape variables calculated using hadronic jets are studied in inclusive multijet events using data corresponding to an integrated luminosity of 139 fb−1. Measurements are performed in bins of jet multiplicity and in different ranges of the scalar sum of the transverse momenta of the two leading jets, reaching scales beyond 2 TeV. These measurements are compared with predictions from Monte Carlo event generators containing leading-order or next-to-leading order matrix elements matched to parton showers simulated to leading-logarithm accuracy. At low jet multiplicities, shape discrepancies between the measurements and the Monte Carlo predictions are observed. At high jet multiplicities, the shapes are better described but discrepancies in the normalisation are observed.
Highlights
A measurement of event-shape variables in p√roton-proton collisions at large momentum transfer is presented using data collected at s = 13 TeV with the ATLAS detector at the Large Hadron Collider
The normalisation factors for Herwig based on angle-ordered showers and Sherpa predictions increase as a function of HT2, whereas a very small dependence of these factors on HT2 is observed for Herwig 7 based on dipole showers, MG5_aMC and Pythia predictions
An excellent description of the inclusive dijet production cross section is found for the Herwig 7 prediction based on dipole showers, whereas Herwig 7 prediction based on angle-ordered showers underestimates it, at most by 9%
Summary
The ATLAS detector [18] at the LHC covers nearly the entire solid angle around the collision point. It consists of an inner charged-particle tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroidal magnets. The ATLAS detector [18] at the LHC covers nearly the entire solid angle around the collision point.1 It consists of an inner charged-particle tracking detector surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroidal magnets. Closest to the interaction point, the high-granularity silicon pixel detector covers the vertex region and typically provides four measurements per track, with the first hit normally recorded in the insertable B-layer installed before Run 2 [19, 20]. It is followed by the silicon microstrip tracker, which usually provides eight measurements per track. The first-level trigger accepts events from the 40 MHz bunch crossings at a rate below 100 kHz, which the high-level trigger further reduces in order to record events to disk at about 1 kHz
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