Measurements of inclusive jet spectra in $pp$ and central Pb-Pb collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$

This article reports measurements of the $p_{\mathrm{T}}$-differential inclusive jet cross section in $pp$ collisions at $\sqrt{s}=5.02\mathrm{TeV}$ and the $p_{\mathrm{T}}$-differential inclusive jet yield in $\text{Pb-Pb}$ 0–10% central collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. Jets were reconstructed at midrapidity with the ALICE tracking detectors and electromagnetic calorimeter using the anti-$k_{\mathrm{T}}$ algorithm. For $pp$ collisions, we report jet cross sections for jet resolution parameters $R=0.1–0.6$ over the range $20<p_{\mathrm{T},\mathrm{jet}}<140$ $\mathrm{GeV}/c$, as well as the jet cross-section ratios of different $R$ and comparisons to two next-to-leading-order (NLO)–based theoretical predictions. For $\text{Pb-Pb}$ collisions, we report the $R=0.2$ and $R=0.4$ jet spectra for $40<p_{\mathrm{T},\mathrm{jet}}<140$ $\mathrm{GeV}/c$ and $60<p_{\mathrm{T},\mathrm{jet}}<140$ $\mathrm{GeV}/c$, respectively. The scaled ratio of jet yields observed in $\text{Pb-Pb}$ to $pp$ collisions, $R_{\mathrm{AA}}$, is constructed, and exhibits strong jet quenching and a clear $p_{\mathrm{T}}$ dependence for $R=0.2$. No significant $R$ dependence of the jet $R_{\mathrm{AA}}$ is observed within the uncertainties of the measurement. These results are compared to several theoretical predictions.

Figure 1

Left: Unfolded $pp$ full jet cross section at $\sqrt{s}=5.02\mathrm{TeV}$ for $R=0.1–0.6$. No leading track requirement is imposed. Right: Ratio of NLO+NLL+NP and powheg+pythia8 tune A14 predictions to the measured data. The systematic uncertainties in the ratio are denoted by boxes and are the quadratic sum of the systematic uncertainties in data and the predictions. Note that no systematic uncertainties for the nonperturbative correction in the NLO+NLL+NP prediction were included.

Figure 2

Nonperturbative correction factor applied to parton-level NLO+NLL predictions, obtained from pythia8 tune A14 as the ratio of the inclusive jet spectrum at hadron-level with MPI compared to parton-level without MPI.

Figure 3

Unfolded $pp$ jet cross-section ratios for various $R$. Top panels: ratios of $R=0.2$ to other radii. Bottom panels: ratios of $R=0.1$ to other radii. The left panels include comparisons to powheg+pythia8, and the right panels include comparisons to NLO+NLL+NP. The experimental correlated systematic uncertainties and shape systematic uncertainties were combined in quadrature into a single systematic uncertainty. Note that no systematic uncertainties for the nonperturbative correction in the NLO+NLL+NP prediction were included.

Figure 4

Unfolded $pp$ and $\text{Pb-Pb}$ full jet spectra at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ for $R=0.2$ (left), with 5 $\mathrm{GeV}/c$ leading track requirement, and $R=0.4$ (right), with 7 $\mathrm{GeV}/c$ leading track requirement. The $pp$ data points correspond to $\frac{d^2\sigma }{d{p}_{\mathrm{T},\mathrm{jet}}d{\eta }_{\mathrm{jet}}}$.

Figure 5

Left: Ratio of the $pp$ jet cross section with various leading charged particle requirements. Right: Ratio of the $R=0.2$ $\text{Pb-Pb}$ jet cross section with a 7 $\mathrm{GeV}/c$ leading charged particle requirement compared to a 5 $\mathrm{GeV}/c$ leading charged particle requirement.

Figure 6

Jet $R_{\mathrm{AA}}$ at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ for $R=0.2$ (left) and $R=0.4$ (right). In the top panel, a leading track requirement is imposed on the $pp$ reference, while in the bottom panel no such requirement is imposed on the $pp$ reference. The combined $〈T_{\mathrm{AA}}〉$ uncertainty and $pp$ luminosity uncertainty of 2.8% is illustrated as a band on the dashed line at $R_{\mathrm{AA}}=1$.

Figure 7

Jet $R_{\mathrm{AA}}$ at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ for $R=0.2$ (left) and $R=0.4$ (right) compared to LBT, ${\mathrm{SCET}}_G$, hybrid model, and JEWEL predictions. The combined $〈T_{\mathrm{AA}}〉$ uncertainty and $pp$ luminosity uncertainty of 2.8% is illustrated as a band on the dashed line at $R_{\mathrm{AA}}=1$. Systematic uncertainties are only included for the ${\mathrm{SCET}}_G$ and hybrid model predictions; see text for details.

Figure 8

Jet $R_{\mathrm{AA}}$ in 0–10% central $\text{Pb-Pb}$ collisions for $R=0.2$ (left) and $R=0.4$ (right) for all currently published experimental results. Closed markers denote $\sqrt{s_{NN}}=5.02\mathrm{TeV}$, and open markers denote $\sqrt{s_{NN}}=2.76\mathrm{TeV}$.