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| CMS-HIN-13-005 ; CERN-EP-2016-217 | ||
| Measurement of inclusive jet cross sections in pp and PbPb collisions at $ \sqrt{s_{\mathrm{NN}}} = $ 2.76 TeV | ||
| CMS Collaboration | ||
| 17 September 2016 | ||
| Phys. Rev. C 96 (2017) 015202 | ||
| Abstract: Inclusive jet spectra from pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV, collected with the CMS detector at the LHC, are presented. Jets are reconstructed with three different distance parameters (R = 0.2, 0.3 and 0.4) for transverse momentum (${p_{\mathrm{T}}}$) greater than 70 GeV/$c$ and pseudorapidity $| {\eta} | < $ 2. Next-to-leading-order quantum chromodynamic calculations with non-perturbative corrections are found to over-predict jet production cross sections in pp for small distance parameters. The jet nuclear modification factors for PbPb compared to pp collisions, show a steady decrease from peripheral to central events, along with a weak dependence on the jet ${p_{\mathrm{T}}}$. They are found to be independent of the distance parameter in the measured kinematic range. | ||
| Links: e-print arXiv:1609.05383 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Raw subtracted ${p_{\mathrm {T}}}$ for jets reconstructed with the anti-$ {k_{\mathrm {T}}}$ algorithm and a distance parameter of $ {R} = $ 0.3, in the ranges 70 $ < \text {jet} \, {p_{\mathrm {T}}} < $ 80 GeV/$c$ (top panels) and 110 $ < \text {jet} \, {p_{\mathrm {T}}} < $ 130 GeV/$c$ (bottom panels). This quantity is found by taking the difference of the sum of PF candidates within the jet cone and raw jet ${p_{\mathrm {T}}}$. Solid symbols show data, and the histogram is from PYTHIA+HYDJET generated events. |
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Figure 1-a:
Raw subtracted ${p_{\mathrm {T}}}$ for jets reconstructed with the anti-$ {k_{\mathrm {T}}}$ algorithm and a distance parameter of $ {R} = $ 0.3, in the range 70 $ < \text {jet} \, {p_{\mathrm {T}}} < $ 80 GeV/$c$. This quantity is found by taking the difference of the sum of PF candidates within the jet cone and raw jet ${p_{\mathrm {T}}}$. Solid symbols show data, and the histogram is from PYTHIA+HYDJET generated events. |
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Figure 1-b:
Raw subtracted ${p_{\mathrm {T}}}$ for jets reconstructed with the anti-$ {k_{\mathrm {T}}}$ algorithm and a distance parameter of $ {R} = $ 0.3, in the range 110 $ < \text {jet} \, {p_{\mathrm {T}}} < $ 130 GeV/$c$. This quantity is found by taking the difference of the sum of PF candidates within the jet cone and raw jet ${p_{\mathrm {T}}}$. Solid symbols show data, and the histogram is from PYTHIA+HYDJET generated events. |
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Figure 2:
Average raw subtracted ${p_{\mathrm {T}}}$ (left) and its RMS (right) for PF jets reconstructed with the anti-$ {k_{\mathrm {T}}}$ algorithm, with a distance parameter $ {R} = $ 0.3. Symbols represent data, and lines show PYTHIA+HYDJET simulated events. |
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Figure 2-a:
Average raw subtracted ${p_{\mathrm {T}}}$ for PF jets reconstructed with the anti-$ {k_{\mathrm {T}}}$ algorithm, with a distance parameter $ {R} = $ 0.3. Symbols represent data, and lines show PYTHIA+HYDJET simulated events. |
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Figure 2-b:
RMS of the average raw subtracted ${p_{\mathrm {T}}}$ for PF jets reconstructed with the anti-$ {k_{\mathrm {T}}}$ algorithm, with a distance parameter $ {R} = $ 0.3. Symbols represent data, and lines show PYTHIA+HYDJET simulated events. |
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Figure 3:
Misreconstructed jet fraction of the inclusive jet spectra, derived from the minimum bias sample, as a function of reconstructed jet ${p_{\mathrm {T}}}$, for various centralities and three different distance parameters (left: $ {R} = $ 0.2, center: $ {R} = $ 0.3, and right: $ {R} = $ 0.4). The correction factor is the average of the dijet selection and trigger object methods discussed in the text. |
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Figure 4:
Comparison of the inclusive jet cross section for anti-$ {k_{\mathrm {T}}}$ jets with distance parameters of $ {R} = $ 0.2 (left), 0.3 (middle) and 0.4 (right), measured for pp collisions at 2.76 TeV (black plus markers), and NLO calculations, at the same collision energy, with NNPDF 2.1 (red star) and CT10N (blue triangle), with their respective NP corrections added. The bottom panels show the ratio of measured cross section to theory calculations. The systematic uncertainties for data are shown in the gray shaded band, while the systematic uncertainties in the NLO calculations are shown with the respective color shaded bands. |
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Figure 5:
Inclusive jet spectra for PbPb jets of distance parameter $ {R} = $ 0.2, in different centrality bins, and pp reference data. The PbPb jet spectra for different centrality classes are scaled by $ < {T_\mathrm {AA}} > $ and multiplied by a different factor for better visualization. Vertical bars represent statistical uncertainty (too small to see on this scale) with the systematical uncertainty in the colored boxes around the data points. |
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Figure 6:
Inclusive jet spectra for PbPb jets of distance parameter $ {R} = $ 0.3, in different centrality bins, and pp reference data. The PbPb jet spectra for different centrality classes are scaled by $ < {T_\mathrm {AA}} > $ and multiplied by a different factor for better visualization. Vertical bars represent statistical uncertainty (too small to see on this scale) with the systematical uncertainty in the colored boxes around the data points. |
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Figure 7:
Inclusive jet spectra for PbPb jets of distance parameter $ {R} = $ 0.4, in different centrality bins, and pp reference data. The PbPb jet spectra for different centrality classes are scaled by $ < {T_\mathrm {AA}} > $ and multiplied by a different factor for better visualization. Vertical bars represent statistical uncertainty (too small to see on this scale) with the systematical uncertainty in the colored boxes around the data points. |
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Figure 8:
Inclusive jet ${{R} _{\mathrm {AA}}}$ as a function of the jet ${p_{\mathrm {T}}}$, for anti-$ {k_{\mathrm {T}}}$ jets with distance parameters $ {R} = $ 0.2 (red stars), 0.3 (black diamonds), and 0.4 (blue crosses) for different centrality bins. The vertical bars (smaller than the markers) indicate the statistical uncertainty and the systematic uncertainty is represented by the bounds of the dotted, solid, and dashed horizontal lines. The uncertainty boxes at unity represent the ${T_\mathrm {AA}}$ and luminosity uncertainty. |
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Figure 9:
Inclusive jet ${{R} _{\mathrm {AA}}}$ for anti-$ {k_{\mathrm {T}}}$ jets with distance parameters $ {R} = $ 0.2 (red stars), 0.3 (black diamonds), and 0.4 (blue crosses), as a function of the average $N_{\text {part}}$ for each collision centrality, for jets of 80 $ < {p_{\mathrm {T}}} < $ 90 and 130 $ < {p_{\mathrm {T}}} < $ 150 GeV/$c$, in the left and right panels respectively. Points are shifted to the left ($ {R} = $ 0.2) and right ($ {R} = $ 0.4) for clarity. The statistical uncertainty is indicated by colored vertical lines (smaller than the markers). The systematic uncertainty is represented by the bounds of the dotted, solid, and dashed horizontal lines for the corresponding distance parameters. The uncertainty boxes at unity represent the ${T_\mathrm {AA}}$ and luminosity uncertainty. |
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Figure 9-a:
Inclusive jet ${{R} _{\mathrm {AA}}}$ for anti-$ {k_{\mathrm {T}}}$ jets with distance parameters $ {R} = $ 0.2 (red stars), 0.3 (black diamonds), and 0.4 (blue crosses), as a function of the average $N_{\text {part}}$ for each collision centrality, for jets of 80 $ < {p_{\mathrm {T}}} < $ 90 GeV/$c$. Points are shifted to the left ($ {R} = $ 0.2) and right ($ {R} = $ 0.4) for clarity. The statistical uncertainty is indicated by colored vertical lines (smaller than the markers). The systematic uncertainty is represented by the bounds of the dotted, solid, and dashed horizontal lines for the corresponding distance parameters. The uncertainty boxes at unity represent the ${T_\mathrm {AA}}$ and luminosity uncertainty. |
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Figure 9-b:
Inclusive jet ${{R} _{\mathrm {AA}}}$ for anti-$ {k_{\mathrm {T}}}$ jets with distance parameters $ {R} = $ 0.2 (red stars), 0.3 (black diamonds), and 0.4 (blue crosses), as a function of the average $N_{\text {part}}$ for each collision centrality, for jets of 130 $ < {p_{\mathrm {T}}} < $ 150 GeV/$c$. Points are shifted to the left ($ {R} = $ 0.2) and right ($ {R} = $ 0.4) for clarity. The statistical uncertainty is indicated by colored vertical lines (smaller than the markers). The systematic uncertainty is represented by the bounds of the dotted, solid, and dashed horizontal lines for the corresponding distance parameters. The uncertainty boxes at unity represent the ${T_\mathrm {AA}}$ and luminosity uncertainty. |
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Figure 10:
Left Panel: Inclusive jet ${{R} _{\mathrm {AA}}}$ as a function of the jet ${p_{\mathrm {T}}}$, for anti-$ {k_{\mathrm {T}}}$ jets with distance parameter $ {R} = $ 0.2 in the 0%-10% centrality bin for CMS (closed circles) and ALICE (pluses) [27]. Right Panel: Inclusive jet ${{R} _{\mathrm {AA}}}$ as a function of the jet ${p_{\mathrm {T}}}$, for anti-$ {k_{\mathrm {T}}}$ jets with distance parameter $ {R} = $ 0.4 in the 0%-10% centrality bin for CMS (closed circles) and ATLAS (diamonds) [26]. The vertical bars indicate the statistical uncertainty. The systematic uncertainty is represented by the bounds of the boxes. The uncertainty boxes at unity represent the ${T_\mathrm {AA}}$ and luminosity uncertainty, open for CMS and shaded for ALICE and ATLAS. See text for a further discussion of differences in the analyses used by the three collaborations. |
| Tables | |
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Table 1:
Summary of the systematic uncertainties in the PbPb jet yield for the central (0-5%), peripheral (70-90%) bins, and the pp jet cross section. Each column showcases the total systematic uncertainties for the corresponding source for the different $ {R} $ and two jet ${p_{\mathrm {T}}}$ ranges i.e. 70 $ < \text {jet} \, {p_{\mathrm {T}}} < $ 80 GeV/$c$ and 250 $ < \text {jet} \, {p_{\mathrm {T}}} < $ 300 GeV/$c$). The $ {T_\mathrm {AA}} $ uncertainties are not shown in the table. Other sources mentioned in the text that are smaller than 1% are not listed explicitly below. |
| Summary |
| The cross section of anti-$k_{\mathrm{T}}$ particle-flow jets has been measured in pp and PbPb collisions at $\sqrt{s_{\mathrm{NN}}} = $ 2.76 TeV for distance parameters ${R} = $ 0.2, 0.3, and 0.4 in $| {\eta} | < $ 2 and for jet ${p_{\mathrm{T}}} $ above 70 GeV/$c$. It is found that next-to-leading order calculations with non-perturbative corrections over predict the pp cross sections, with a smaller discrepancy for larger distance parameters. The PbPb inclusive jet nuclear modification factors show a steady decrease from peripheral to central events, with a slight rise with jet ${p_{\mathrm{T}}}$. No significant dependence of the jet nuclear modification factor on the distance parameter is found for the jets in the kinematic range measured in this analysis. |
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