Measurement of the jet fragmentation function and transverse profile in proton-proton collisions at a center-of-mass energy of 7 TeV with the ATLAS detector

TL;DR

This study reports ATLAS measurements of jet fragmentation and transverse jet structure in proton–proton collisions at $\sqrt{s}=7$ TeV, using jets in $25< p_{\mathrm{T,jet}}<500$ GeV and $|\eta_{\mathrm{jet}}|<1.2$, with a data set of ${\mathcal L}=36\,\mathrm{pb}^{-1}$. The authors extract corrected distributions $F(z,p_{\mathrm{T,jet}})$, $f(p_{\mathrm{T}}^{\mathrm{rel}},p_{\mathrm{T,jet}})$, and $\rho_{ch}(r,p_{\mathrm{T,jet}})$ via Bayesian unfolding and compare them to multiple MC tunes. They find that while some tunes (notably AMBT1 Pythia and Perugia2010) describe the fragmentation function well, none reproduce both the fragmentation and the transverse jet profile across the full kinematic range; the $p_{\mathrm{T}}^{\mathrm{rel}}$ distributions, in particular, are not well described by any generator within uncertainties. The results provide important data-driven constraints for tuning non-perturbative QCD aspects of jet fragmentation and underlying-event models, and are available in HEPData/Rivet for broader use.

Abstract

The jet fragmentation function and transverse profile for jets with 25 GeV < ptJet < 500 GeV and etaJet<1.2 produced in proton-proton collisions with a center-of-mass energy of 7 TeV are presented. The measurement is performed using data with an integrated luminosity of 36 pb^-1. Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function. None of these choices reproduce both the transverse profile and fragmentation function over the full kinematic range of the measurement.

Figures (14)

• Figure 1: Systematic uncertainty in $F(z,p_{\mathrm{T\,jet}})$ from uncertainties in the jet energy scale and resolution, the track reconstruction efficiency and momentum resolution and the response matrix for $25\ {\rm GeV} <p_{\mathrm{T\,jet}} < 40\ {\rm GeV}$ (left) and $400\ {\rm GeV} < p_{\mathrm{T\,jet}} < 500\ {\rm GeV}$ (right). The total uncertainty from the combination is also shown.
• Figure 2: Systematic uncertainty in $f(p_{\mathrm{T}}^{rel},p_{\mathrm{T\,jet}})$ from uncertainties in the jet energy scale and resolution, the track reconstruction efficiency and momentum resolution and the response matrix for $25\ {\rm GeV} <p_{\mathrm{T\,jet}} < 40\ {\rm GeV}$ (left) and $400\ {\rm GeV} < p_{\mathrm{T\,jet}} < 500\ {\rm GeV}$ (right). The total uncertainty from the combination is also shown.
• Figure 3: Systematic uncertainty in $\rho_{ch}(r,p_{\mathrm{T\,jet}})$ from uncertainties in the jet energy scale and resolution, the track reconstruction efficiency and momentum resolution and the response matrix for $25\ {\rm GeV} <p_{\mathrm{T\,jet}} < 40\ {\rm GeV}$ (left) and $400\ {\rm GeV} < p_{\mathrm{T\,jet}} < 500\ {\rm GeV}$ (right). The total uncertainty from the combination is also shown.
• Figure 4: Distributions of $F(z)$ for $25\ {\rm GeV} < p_{\mathrm{T\,jet}} < 40\ {\rm GeV}$ (left) and $400\ {\rm GeV} < p_{\mathrm{T\,jet}} < 500\ {\rm GeV}$ (right). The gray band indicates the total uncertainty.
• Figure 5: Distributions of $F(z)$ in bins of $p_{\mathrm{T\,jet}}$. The circles show unfolded data and the lines are the predictions from AMBT1 Pythia.