Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV

TL;DR

This work documents a comprehensive, data-driven calibration of jet energy scale and resolution for CMS in pp collisions at 8 TeV, combining pileup offset corrections, simulated detector response, and residual data–MC corrections across multiple channels (Z+jet, gamma+jet, dijet, multijet). A global chi^2 fit coherently propagates uncertainties and correlations, yielding uncertainties below 3% across most of the phase space and a 0.32% precision benchmark for central jets, setting a new standard for hadron-collider JES. The analysis also scrutinizes jet flavor and jet-size dependencies and provides robust JER measurements via complementary methods (dijet and gamma+jet), with detailed cross-checks in b-jet contexts and PF jet composition studies. Overall, the methodology delivers precise, correlated JES/JER corrections essential for precision CMS physics analyses at the LHC.

Abstract

Improved jet energy scale corrections, based on a data sample corresponding to an integrated luminosity of 19.7 inverse-femtobarns collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 8 TeV, are presented. The corrections as a function of pseudorapidity eta and transverse momentum pT are extracted from data and simulated events combining several channels and methods. They account successively for the effects of pileup, uniformity of the detector response, and residual data-simulation jet energy scale differences. Further corrections, depending on the jet flavor and distance parameter (jet size) R, are also presented. The jet energy resolution is measured in data and simulated events and is studied as a function of pileup, jet size, and jet flavor. Typical jet energy resolutions at the central rapidities are 15-20% at 30 GeV, about 10% at 100 GeV, and 5% at 1 TeV. The studies exploit events with dijet topology, as well as photon+jet, Z+jet and multijet events. Several new techniques are used to account for the various sources of jet energy scale corrections, and a full set of uncertainties, and their correlations, are provided. The final uncertainties on the jet energy scale are below 3% across the phase space considered by most analyses (pT > 30 GeV and abs(eta) < 5.0). In the barrel region (abs(eta) < 1.3) an uncertainty below 1% for pT > 30 GeV is reached, when excluding the jet flavor uncertainties, which are provided separately for different jet flavors. A new benchmark for jet energy scale determination at hadron colliders is achieved with 0.32% uncertainty for jets with pT of the order of 165-330 GeV, and abs(eta) < 0.8.

Figures (47)

• Figure 1: Average value of the ratio of measured jet $p_{\mathrm{T}}$ to particle-level jet $p_\text{T, ptcl}$ in QCD MC simulation, in bins of $p_\text{T, ptcl}$, at various stages of JEC: before any corrections (left), after pileup offset corrections (middle), after all JEC (right). Here $\mu$ is the average number of pileup interactions per bunch crossing.
• Figure 2: Consecutive stages of JEC, for data and MC simulation. All corrections marked with MC are derived from simulation studies, RC stands for random cone, and MJB refers to the analysis of multijet events.
• Figure 3: Comparison of data (circles) and pythia6.4 simulation (histograms) for the distributions of the number of reconstructed primary vertices $N_\mathrm{PV}$ (left), and of the offset energy density $\rho$ (right).
• Figure 4: Mean of the number of good primary vertices per event, $\langle N_\mathrm{PV}\rangle$ (left), and mean diffuse offset energy density, $\langle\rho\rangle$ (right), versus the average number of pileup interactions per bunch crossing, $\mu$, for data (circles) and pythia6.4 simulation (diamonds).
• Figure 5: Simulated particle-level offset $\langle p_\mathrm{T, offset~ptcl}\rangle$ defined in Eq. (\ref{['eq:offsetptcl']}) (left), and residual offset after correcting for pileup with Eq. (\ref{['eq:chybrid']}) (right) for $\lvert \eta \rvert<1.3$, versus particle jet $p_{\mathrm{T}}$, for different values of average number of pileup interactions per bunch crossing $\langle\mu\rangle$.