[Mean jet p_T vs number of vertices]

Average reconstructed jet p_T at the EM scale versus the number of reconstructed primary vertices (N_PV), for matched truth-jet p_T between 20 and 25 GeV. Requiring that all matched tracks originate from the hard scatter (JVF = 1) reduces the pile-up induced p_T offset by roughly 40%, indicating that tracks effectively describe only 40% of the impact of pile-up on reconstructed jets.

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[Response vs the true jet p_T]

Calorimeter response to central jets at the LCW scale, as a function of the MC truth jet p_T. The p_T offset induced by a mean of 40 pile-up interactions (⟨μ⟩ = 40) causes a shift in the reconstructed jet p_T of approximately 25 GeV. Application of an average offset correction, parametrized by the number of reconstructed primary vertices (N_PV), recovers the response observed in the absence of pile-up (⟨μ⟩ = 0).

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[Subtraction of in-time pile-up using the “jet areas” method, central]

Average MC truth-based jet p_T offset at the LCW scale versus the number of reconstructed primary vertices (N_PV). Out-of-time pile-up is constrained by using only events with 5 < ⟨μ⟩ < 6. In the central region (0.0 < |η| < 0.3) the jet areas correction removes the impact of in-time pile-up on the jet p_T, though a small overcorrection is apparent.

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[Subtraction of in-time pile-up using the “jet areas” method, forward]

Average MC truth-based jet p_T offset at the LCW scale versus the number of reconstructed primary vertices (N_PV). Out-of-time pile-up is constrained by using only events with 5 < ⟨μ⟩ < 6. In the forward region (3.6 < |η| < 4.5), the jet areas correction removes the impact of in-time pile-up on the jet p_T, though a small overcorrection is apparent.

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[Subtraction of out-of-time pile-up using the “jet areas” method, central]

Average MC truth-based jet p_T offset at the LCW scale versus the average number of interactions per bunch crossing (⟨μ⟩), which is sensitive to out-of-time pile-up. In-time pile-up is constrained by using only events with N_PV = 6. In the central region (0.0 < |η| < 0.3), the jet areas correction over-corrects slightly for the impact of out-of-time pile-up.

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[Subtraction of out-of-time pile-up using the “jet areas” method, forward region]

Average MC truth-based jet p_T offset at the LCW scale versus the average number of interactions per bunch crossing (⟨μ⟩), which is sensitive to out-of-time pile-up. In-time pile-up is constrained by using only events with N_PV = 6. In the forward region (3.6 < |η| < 4.5), sensitivity to out-of-time pile-up is substantially different then in the central region. Since we calculate rho in the central region, the jet areas correction does not account for the impact of out-of-time pile-up on forward jets

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[Jet multiplicity vs number of vertices]

Average multiplicity of pile-up jets with LCW-scale p_T > 20 GeV versus the number of reconstructed primary vertices (N_PV) before and after correcting for the p_T offset induced by pile-up, in simulated dijet events with a mean of 20 overlaid pile-up interactions. The average offset correction, parametrized by N_PV, shifts up to 90% of pile-up jets below the p_T threshold. By estimating the pile-up offset event by event using low-p_T calorimeter deposits, the jet areas correction rejects a substantial fraction of the remaining 10%.

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[Jet multiplicity of pile-up jets vs number of vertices]

Average multiplicity of pile-up jets with LCW-scale p_T > 20 GeV versus the number of reconstructed primary vertices (N_PV) after correcting for the p_T offset induced by pile-up, in simulated dijet events with a mean of 20 overlaid pile-up interactions (⟨μ⟩). There is a significant residual number of pile-up jets, even after the jet areas correction. To reject the remaining jets, we can use tracking information. Pile-up jets are virtually eliminated by requiring at least a quarter of the matched track p_T to come from the hard scatter vertex (JVF > 0.25).

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[Jet resolution for various pile-up subtraction methods]

The width of the MC truth-based jet p_T offset at the LCW scale, in a sample with zero pile-up (⟨μ⟩ = 0), compared to a mean of 40 pile-up interactions, before and after correcting for the p_T offset induced by pile-up. Pile-up increases the width by nearly a factor of 3, and the average offset correction does not help to recover this degradation in resolution. However, the jet areas correction recovers 30-40% of the degradation. The remaining 60-70% is due to localized fluctuations in pile-up, which may be reduced by using information from tracks matched to jets.

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[Track-based pile-up activity vs calorimeter based]

Track-based local versus global estimates of pile-up activity in a jet, in simulated events with a mean of 40 pile-up interactions. For a given amount of global pile-up activity, there are significant fluctuations in the activity that is directly affecting a specific jet.

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