Study of Jet Shapes in Inclusive Jet Production in pp Collisions at sqrt(s) = 7 TeV using the ATLAS Detector

TL;DR

This ATLAS study measures differential and integrated jet shapes in inclusive jet production at sqrt(s)=7 TeV using 3 pb^-1, correcting for detector effects and comparing to LO matrix-element plus parton-shower MC predictions. The jet shapes reveal jets become narrower with higher pT and show mild rapidity dependence, highlighting sensitivity to parton shower, fragmentation, and underlying event models. Among MC predictions, PYTHIA-Perugia2010 best describes the data, while alternative tunes and generators exhibit systematic deviations, especially at low pT or with/without UE modeling. These results demonstrate the potential of jet-shape observables at the LHC to constrain soft radiation, UE activity, and non-perturbative fragmentation in MC models, informing future tuning and theory developments.

Abstract

Jet shapes have been measured in inclusive jet production in proton-proton collisions at sqrt(s) = 7 TeV using 3 pb^{-1} of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30 GeV < pT < 600 GeV and rapidity in the region |y| < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and non-perturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described.

Figures (7)

• Figure 1: The measured differential jet shape, $\rho(r)$, in inclusive jet production for jets with $|y| < 2.8$ and $30 \ {\rm GeV} < p_{ T} < 110 \ {\rm GeV}$ is shown in different $p_{ T}$ regions. Error bars indicate the statistical and systematic uncertainties added in quadrature. The predictions of PYTHIA-Perugia2010 (solid lines), HERWIG++ (dashed lines), ALPGEN interfaced with HERWIG and JIMMY (dotted lines), and PYTHIA-MC09 (dashed-dotted lines) are shown for comparison.
• Figure 2: The measured differential jet shape, $\rho(r)$, in inclusive jet production for jets with $|y| < 2.8$ and $110 \ {\rm GeV} < p_{ T} < 310 \ {\rm GeV}$ is shown in different $p_{ T}$ regions. Error bars indicate the statistical and systematic uncertainties added in quadrature. The predictions of PYTHIA-Perugia2010 (solid lines), HERWIG++ (dashed lines), ALPGEN interfaced with HERWIG and JIMMY (dotted lines), and PYTHIA-MC09 (dashed-dotted lines) are shown for comparison.
• Figure 3: The measured differential jet shape, $\rho(r)$, in inclusive jet production for jets with $|y| < 2.8$ and $310 \ {\rm GeV} < p_{ T} < 600 \ {\rm GeV}$ is shown in different $p_{ T}$ regions. Error bars indicate the statistical and systematic uncertainties added in quadrature. The predictions of PYTHIA-Perugia2010 (solid lines), HERWIG++ (dashed lines), ALPGEN interfaced with HERWIG and JIMMY (dotted lines), and PYTHIA-MC09 (dashed-dotted lines) are shown for comparison.
• Figure 4: The measured integrated jet shape, $1 - \Psi(r=0.3)$, as a function of $p_{ T}$ for jets with $|y| < 2.8$ and $30 \ {\rm GeV} < p_{ T} < 600 \ {\rm GeV}$. Error bars indicate the statistical and systematic uncertainties added in quadrature. The data are compared to the predictions of: (a) PYTHIA-Perugia2010 (solid lines), HERWIG++ (dashed lines), ALPGEN interfaced with HERWIG and JIMMY (dotted lines), and PYTHIA-MC09 (dashed-dotted lines); (b) PYTHIA-Perugia2010 (solid lines), PYTHIA-Perugia2010 without UE (dotted lines), and PYTHIA-DW (dashed lines).
• Figure 5: The measured integrated jet shape, $1 - \Psi(r=0.3)$, as a function of $|y|$ for jets with $|y| < 2.8$ and $30 \ {\rm GeV} < p_{ T} < 400 \ {\rm GeV}$. Error bars indicate the statistical and systematic uncertainties added in quadrature. The predictions of PYTHIA-Perugia2010 (solid lines), HERWIG++ (dashed lines), ALPGEN interfaced with HERWIG and JIMMY (dotted lines), PYTHIA-MC09 (dashed-dotted lines), and PYTHIA-DW (dashed-dotted-dotted lines) are shown for comparison.