Jet substructure at very high luminosity

Efficiency to select hard-scatter jets when imposing a pileup jet suppression selection of RpT>0.2. Hard-scatter jets are defined as jets matched within DR<0.3 to a truth jet with pT>10 GeV. RpT is defined as the scalar pT sum of the tracks that are assigned to the jet and originate from the hard-scatter vertex divided by the fully calibrated jet pT, as described in Ref. [1]. RpT is computed using truth Monte Carlo charged particles with pT >1 GeV smeared with resolution functions to simulate reconstructed tracks. Smearing functions were determined from studies of single-track resolution in the ITK LOI_VF geometry with 50 micrometer pixel size. Two different smearing functions are consider, one for the z0 resolution, where z0 is the track impact parameter in the z-axis, and another for the track pT resolution. Tracks used to compute RpT are required to have after the smearing a z0 impact parameter within 2mm of the truth primary vertex position. The figure shows the jet efficiency for jets with pT between 20 and 30 GeV.

Efficiency to select hard-scatter jets when imposing a pileup jet suppression selection of RpT>0.2. Hard-scatter jets are defined as jets matched within DR<0.3 to a truth jet with pT>10 GeV. RpT is defined as the scalar pT sum of the tracks that are assigned to the jet and originate from the hard-scatter vertex divided by the fully calibrated jet pT, as described in Ref. [1]. RpT is computed using truth Monte Carlo charged particles with pT >1 GeV smeared with resolution functions to simulate reconstructed tracks. Smearing functions were determined from studies of single-track resolution in the ITK LOI_VF geometry with 50 micrometer pixel size. Two different smearing functions are consider, one for the z0 resolution, where z0 is the track impact parameter in the z-axis, and another for the track pT resolution. Tracks used to compute RpT are required to have after the smearing a z0 impact parameter within 2mm of the truth primary vertex position. The figure shows the jet efficiency for jets with pT between 30 and 40 GeV.

Fake rate of pileup jets as a function of hard-scatter jet efficiency when applying different RpT selection values, for jets with pT between 20 and 30 GeV. Hard-scatter jets are matched within DR<0.3 to a truth jet with pT>10 GeV. Pile-up jets are required to have a minimal DR>0.6 from any truth jet with pT>4 GeV. RpT is defined as the scalar pT sum of the tracks that are assigned to the jet and originate from the hard-scatter vertex divided by the fully calibrated jet pT, as described in [1]. RpT is computed using truth Monte Carlo charged particles with pT >1 GeV smeared with resolution functions to simulate reconstructed tracks. Smearing functions were determined from studies of single-track resolution in the ITK LOI_VF geometry with 50 micrometer pixel size. Two different smearing functions are consider, one for the z0 resolution, where z0 is the track impact parameter in the z-axis, and another for the track pT resolution. Tracks used to compute RpT are required to have after the smearing a z0 impact parameter within 2mm of the truth primary vertex position. The eta dependence of the pile-up jets rejection when not smearing is applied is due to the topological limitation of the hard-scatter and pile-up jets definition.

This figure has been revised on 30 October 2014 fixing a bug affecting the black curve with empty markers

Fake rate of pileup jets as a function of hard-scatter jet efficiency when applying different RpT selection values, for jets with pT between 30 and 40 GeV (right). Hard-scatter jets are matched within DR<0.3 to a truth jet with pT>10 GeV. Pile-up jets are required to have a minimal DR>0.6 from any truth jet with pT>4 GeV. RpT is defined as the scalar pT sum of the tracks that are assigned to the jet and originate from the hard-scatter vertex divided by the fully calibrated jet pT, as described in [1]. RpT is computed using truth Monte Carlo charged particles with pT >1 GeV smeared with resolution functions to simulate reconstructed tracks. Smearing functions were determined from studies of single-track resolution in the ITK LOI_VF geometry with 50 micrometer pixel size. Two different smearing functions are consider, one for the z0 resolution, where z0 is the track impact parameter in the z-axis, and another for the track pT resolution. Tracks used to compute RpT are required to have after the smearing a z0 impact parameter within 2mm of the truth primary vertex position. The eta dependence of the pile-up jets rejection when not smearing is applied is due to the topological limitation of the hard-scatter and pile-up jets definition.

This figure has been revised on 30 October 2014 fixing a bug affecting the black curve with empty markers

Missing ET resolution as a function of the total transverse energy in the event calculated by summing the total transverse energy in the calorimeter in dijet events, for three different missing ET settings. Missing ET in dijet events has two main contributions, a jet term, computed from reconstructed jets above 20 GeV, and a soft term, computed from all charged tracks within the tracker acceptance. A forward tracker can improve the performance of the missing ET in two different ways: by extending the acceptance of the soft term to include forward tracks, and by providing suppression of fake pileup jets above 20 GeV using the RpT selection [1]. Both the missing ET soft term and RpT are computed using truth Monte Carlo charged particles with pT >1 GeV and smeared with resolution functions to simulate reconstructed tracks. Smearing functions were determined from studies of single-track resolution in the ITK LOI_VF geometry. The resolution for the LHC Run 1 ATLAS detector, which uses tracks with pT>0.5 GeV, is shown in black. In red is the resolution obtained combining the forward soft term with pileup jet suppression.