A simple description of jet cross-section ratios

TL;DR

This paper tackles predicting the ratio ${\cal R}(p_t;R_1,R_2)$ of inclusive jet cross-sections computed with the same jet algorithm at two radii. It demonstrates that ${\cal R}$ can be computed to ${\cal O}(\alpha_s^2)$ by an explicit perturbative expansion, taking differences of cross-sections at fixed order to avoid the NNLO barrier. It also estimates universal non-perturbative corrections from soft-gluon emission using the Milan factor $M$ and the infrared parameter ${\alpha_0(\mu_I)}$, folded into the observable via ${K_{\rm hadr}}$. The phenomenology at RHIC and LHC shows sizable corrections at RHIC and smaller corrections at the LHC, indicating reduced theoretical uncertainties for the ratio and providing a testbed for pQCD and hadronisation models, with prospects for NNLO refinements via loopsim.

Abstract

We compute the ratio of the inclusive jet cross-sections obtained with the same jet algorithm at two different values of the jet radius. We perform a computation of that observable at NLO (O(alphas^2)) in perturbative QCD and compute non-perturbative corrections from soft-gluon emission. We discuss predictions for RHIC and the LHC.

Figures (2)

• Figure 1: QCD predictions for the ratio ${\cal R}(p_t;0.2,0.4)$ at RHIC ($\sqrt{s}=200\,\mathrm{GeV}$) for the anti-$k_t$ (left) and $k_t$ (right) jet algorithms. On the top panel, the solid lines correspond, from top to bottom, to the LO QCD computation (green), to the NLO QCD ratio (red) and to the NLO QCD computation including hadronisation effects (blue). The uncertainties due to the scale choice and, when relevant, hadronisation are shown as shaded bands on the top panel and the relative scale uncertainty is plotted on the bottom panel. For comparison, we have also plotted in dashed lines the parton-level (red) and hadron-level (blue) predictions from Pythia.
• Figure 2: Left: comparison of our inclusive jet cross-section computations with the ATLAS measurements. The ratio between the experimental values and the theory predictions (NLO QCD including non-perturbative effects) is plotted; the yellow band represents the uncertainty on the theoretical prediction and the cyan band corresponds to the NLO QCD prediction without hadronisation corrections. Right: predictions for the ratio ${\cal R}(p_t;0.4,0.6)$ for the anti-$kt$ algorithm at ,from top to bottom, LO, NLO, NLO with hadronisation corrections. See Fig. \ref{['fig:star']} for conventions.