CMS-PAS-FTR-18-027 | ||
Constraining nuclear parton distributions with heavy ion collisions at the HL-LHC with the CMS experiment | ||
CMS Collaboration | ||
December 2018 | ||
Abstract: Recent measurements in heavy ion collisions by the CERN LHC Collaborations have been used to assess nuclear effects and provide valuable data for nuclear parton distribution analyses. In this note, performance studies for measurements with the CMS detector at the High-Luminosity LHC (HL-LHC) are presented. These include the coherent $\Upsilon(1\text{S})$ photoproduction in ultraperipheral lead-lead collisions, corresponding to a total integrated luminosity of 10 nb$^{-1}$ at a nucleon-nucleon (NN) center-of-mass energy ($\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}}$) of 5.5 TeV. This note also presents the performance studies at the HL-LHC for analyses of inclusive Z boson, dijet, and top quark pair production in proton-lead collisions at $\sqrt{\smash [b]{s_{_{\mathrm {NN}}}}}= $ 8.16 TeV for an integrated luminosity of 2 pb$^{-1}$. | ||
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
Projections for gluon shadowing factor measured with $\Upsilon (1\text{S})$ photoproduction in ultraperipheral PbPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.5 TeV. The error bars represent the statistical uncertainties, and the boxes the systematic ones. The projected data is compared to the central value of the EPS09 global fit [26]. The most dominant uncertainties are those of EPS09 (not shown). |
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Figure 2:
Projections for Z boson differential cross section in pPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 8.16 TeV as a function of the Z boson rapidity in the center-of-mass (CM) frame. The expectations from CT14 PDF and EPPS16 nPDF are also shown. |
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Figure 3:
Distributions of the ${m_{{\mathrm {j} \mathrm {j}^{\prime}}}}$ (top) and ${m_\text {top}}$ (bottom). From left to right the events are classified in the 0, 1, and 2 b-tagged jet categories. The sum of the predictions for the $ {{\mathrm {t}\overline {\mathrm {t}}}} $ signal and background is compared to pseudo-data (sampled randomly from the total of the predictions in each category). The bottom plots show the ratio between the pseudo-data and the sum of the predictions. The shaded band represents the relative uncertainty due to the limited event count in the simulated samples and the estimate of the normalization of the QCD multijet background. |
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Figure 3-a:
Distribution of ${m_{{\mathrm {j} \mathrm {j}^{\prime}}}}$ for events classified in the 0 b-tagged jet category. The sum of the predictions for the $ {{\mathrm {t}\overline {\mathrm {t}}}} $ signal and background is compared to pseudo-data (sampled randomly from the total of the predictions in each category). The bottom plot shows the ratio between the pseudo-data and the sum of the predictions. The shaded band represents the relative uncertainty due to the limited event count in the simulated samples and the estimate of the normalization of the QCD multijet background. |
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Figure 3-b:
Distribution of ${m_{{\mathrm {j} \mathrm {j}^{\prime}}}}$ for events classified in the 1 b-tagged jet category. The sum of the predictions for the $ {{\mathrm {t}\overline {\mathrm {t}}}} $ signal and background is compared to pseudo-data (sampled randomly from the total of the predictions in each category). The bottom plot shows the ratio between the pseudo-data and the sum of the predictions. The shaded band represents the relative uncertainty due to the limited event count in the simulated samples and the estimate of the normalization of the QCD multijet background. |
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Figure 3-c:
Distribution of ${m_{{\mathrm {j} \mathrm {j}^{\prime}}}}$ for events classified in the 2 b-tagged jet category. The sum of the predictions for the $ {{\mathrm {t}\overline {\mathrm {t}}}} $ signal and background is compared to pseudo-data (sampled randomly from the total of the predictions in each category). The bottom plot shows the ratio between the pseudo-data and the sum of the predictions. The shaded band represents the relative uncertainty due to the limited event count in the simulated samples and the estimate of the normalization of the QCD multijet background. |
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Figure 3-d:
Distribution of ${m_\text {top}}$ for events classified in the 0 b-tagged jet category. The sum of the predictions for the $ {{\mathrm {t}\overline {\mathrm {t}}}} $ signal and background is compared to pseudo-data (sampled randomly from the total of the predictions in each category). The bottom plot shows the ratio between the pseudo-data and the sum of the predictions. The shaded band represents the relative uncertainty due to the limited event count in the simulated samples and the estimate of the normalization of the QCD multijet background. |
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Figure 3-e:
Distribution of ${m_\text {top}}$ for events classified in the 1 b-tagged jet category. The sum of the predictions for the $ {{\mathrm {t}\overline {\mathrm {t}}}} $ signal and background is compared to pseudo-data (sampled randomly from the total of the predictions in each category). The bottom plot shows the ratio between the pseudo-data and the sum of the predictions. The shaded band represents the relative uncertainty due to the limited event count in the simulated samples and the estimate of the normalization of the QCD multijet background. |
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Figure 3-f:
Distribution of ${m_\text {top}}$ for events classified in the 2 b-tagged jet category. The sum of the predictions for the $ {{\mathrm {t}\overline {\mathrm {t}}}} $ signal and background is compared to pseudo-data (sampled randomly from the total of the predictions in each category). The bottom plot shows the ratio between the pseudo-data and the sum of the predictions. The shaded band represents the relative uncertainty due to the limited event count in the simulated samples and the estimate of the normalization of the QCD multijet background. |
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Figure 4:
The top panels represent the differential $ {{\mathrm {t}\overline {\mathrm {t}}}} $ production cross section in the visible phase space as a function of the charged lepton ${p_{\mathrm {T}}}$ (left) and rapidity (right) at reconstruction level. The statistical uncertainty in the pseudo-data, represented by the inner error bars, is estimated through the application of the sPlot technique [41]. The outer error bars represent the total uncertainty, assuming a conservative 5% systematic uncertainty envelope. The uncertainty in the {powheg+{pythia}} [36,37,38,39] prediction is shown as a band corresponding to the 68% CL variation envelope of the EPPS16 [29] nPDF eigenvalues. The bottom panels represent the relative uncertainties in the pseudo-data and theory predictions. |
png pdf |
Figure 4-a:
The top panel represents the differential $ {{\mathrm {t}\overline {\mathrm {t}}}} $ production cross section in the visible phase space as a function of the charged lepton ${p_{\mathrm {T}}}$ at reconstruction level. The statistical uncertainty in the pseudo-data, represented by the inner error bars, is estimated through the application of the sPlot technique [41]. The outer error bars represent the total uncertainty, assuming a conservative 5% systematic uncertainty envelope. The uncertainty in the {powheg+{pythia}} [36,37,38,39] prediction is shown as a band corresponding to the 68% CL variation envelope of the EPPS16 [29] nPDF eigenvalues. The bottom panel represents the relative uncertainties in the pseudo-data and theory predictions. |
png pdf |
Figure 4-b:
The top panel represents the differential $ {{\mathrm {t}\overline {\mathrm {t}}}} $ production cross section in the visible phase space as a function of the charged lepton rapidity at reconstruction level. The statistical uncertainty in the pseudo-data, represented by the inner error bars, is estimated through the application of the sPlot technique [41]. The outer error bars represent the total uncertainty, assuming a conservative 5% systematic uncertainty envelope. The uncertainty in the {powheg+{pythia}} [36,37,38,39] prediction is shown as a band corresponding to the 68% CL variation envelope of the EPPS16 [29] nPDF eigenvalues. The bottom panel represents the relative uncertainties in the pseudo-data and theory predictions. |
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Figure 5:
Projections for dijet pseudorapidity distributions for pPb collisions with a total integrated luminosity of 2 pb$^{-1}$. |
Summary |
We have presented a series of performance studies for future measurements in both PbPb and pPb collisions for the High-Luminosity LHC project, putting special emphasis on a selected number of physics analyses that can serve to get insights into nuclear effects and nuclear parton distribution functions with the projected larger sample sizes that are envisaged. |
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Compact Muon Solenoid LHC, CERN |