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CMS-FSQ-16-011 ; CERN-EP-2018-187
Measurement of charged particle spectra in minimum-bias events from proton-proton collisions at $\sqrt{s} = $ 13 TeV
Eur. Phys. J. C 78 (2018) 697
Abstract: Pseudorapidity, transverse momentum, and multiplicity distributions are measured in the pseudorapidity range $|{\eta}| < $ 2.4 for charged particles with transverse momenta satisfying ${p_{\mathrm{T}}} > $ 0.5 GeV in proton-proton collisions at a center-of-mass energy of $\sqrt{s} = $ 13 TeV. Measurements are presented in three different event categories. The most inclusive of the categories corresponds to an inelastic pp data set, while the other two categories are exclusive subsets of the inelastic sample that are either enhanced or depleted in single diffractive dissociation events. The measurements are compared to predictions from Monte Carlo event generators used to describe high-energy hadronic interactions in collider and cosmic-ray physics.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
From top to bottom, left to right: pseudorapidity, $ {p_{\mathrm {T}}} $, leading $ {p_{\mathrm {T}}} $, integrated leading $ {p_{\mathrm {T}}} $, and multiplicity of charged particles per event for the inelastic (circles), NSD-enhanced (triangles), SD-enhanced (diamonds), and SD-One-Side enhanced (crosses) event samples. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point.

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Figure 1-a:
Distribution of the pseudorapidity of charged particles per event for the inelastic (circles), NSD-enhanced (triangles), SD-enhanced (diamonds), and SD-One-Side enhanced (crosses) event samples. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point.

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Figure 1-b:
Distribution of $ {p_{\mathrm {T}}} $ of charged particles per event for the inelastic (circles), NSD-enhanced (triangles), SD-enhanced (diamonds), and SD-One-Side enhanced (crosses) event samples. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point.

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Figure 1-c:
Distribution of the leading $ {p_{\mathrm {T}}} $ of charged particles per event for the inelastic (circles), NSD-enhanced (triangles), SD-enhanced (diamonds), and SD-One-Side enhanced (crosses) event samples. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point.

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Figure 1-d:
Distribution of the integrated leading $ {p_{\mathrm {T}}} $ of charged particles per event for the inelastic (circles), NSD-enhanced (triangles), SD-enhanced (diamonds), and SD-One-Side enhanced (crosses) event samples. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point.

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Figure 1-e:
Distribution of the multiplicity of charged particles per event for the inelastic (circles), NSD-enhanced (triangles), SD-enhanced (diamonds), and SD-One-Side enhanced (crosses) event samples. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point.

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Figure 2:
Charged particle pseudorapidity densities averaged over both positive and negative $ {\eta} $ ranges. Top to bottom, left to right: inelastic, NSD-, SD-, and SD-One-Side enhanced event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panels show the corresponding MC-to-data ratios.

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Figure 2-a:
Charged particle pseudorapidity densities averaged over both positive and negative $ {\eta} $ ranges: inelastic enhanced event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 2-b:
Charged particle pseudorapidity densities averaged over both positive and negative $ {\eta} $ ranges: NSD-enhanced event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 2-c:
Charged particle pseudorapidity densities averaged over both positive and negative $ {\eta} $ ranges: SD-enhanced event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 2-d:
Charged particle pseudorapidity densities averaged over both positive and negative $ {\eta} $ ranges: SD-One-Side enhanced event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 3:
Charged particle multiplicity distributions of the inelastic (left), and NSD-enhanced (right) event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panels show the corresponding MC-to-data ratios.

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Figure 3-a:
Charged particle multiplicity distributions of the inelastic event sample. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 3-b:
Charged particle multiplicity distributions of the NSD-enhanced event sample. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 4:
Charged particle transverse-momentum densities of inelastic (top left), NSD-enhanced (top right), and SD-enhanced (bottom) event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panels show the corresponding MC-to-data ratios.

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Figure 4-a:
Charged particle transverse-momentum densities of the inelastic event sample. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 4-b:
Charged particle transverse-momentum densities of the NSD-enhanced event sample. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 4-c:
Charged particle transverse-momentum densities of the SD-enhanced event sample. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 5:
Leading charged particle $ {p_{\mathrm {T}}} $ distributions of inelastic (top left), NSD-enhanced (top right), and SD-enhanced (bottom) event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panels show the corresponding MC-to-data ratios.

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Figure 5-a:
Leading charged particle $ {p_{\mathrm {T}}} $ distributions of the inelastic event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 5-b:
Leading charged particle $ {p_{\mathrm {T}}} $ distributions of the NSD-enhanced event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 5-c:
Leading charged particle $ {p_{\mathrm {T}}} $ distributions of the SD-enhanced event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 6:
Integrated leading charged particle $ {p_{\mathrm {T}}} $ distributions as a function of ${p_{\text {T,min}}}$ for inelastic (top left), NSD-enhanced (top right), and SD-enhanced (bottom) event samples. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panels show the corresponding MC-to-data ratios.

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Figure 6-a:
Integrated leading charged particle $ {p_{\mathrm {T}}} $ distribution as a function of ${p_{\text {T,min}}}$ for inelastic event sample. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.

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Figure 6-b:
Integrated leading charged particle $ {p_{\mathrm {T}}} $ distribution as a function of ${p_{\text {T,min}}}$ for NSD-enhanced

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Figure 6-c:
Integrated leading charged particle $ {p_{\mathrm {T}}} $ distribution as a function of ${p_{\text {T,min}}}$ for SD-enhanced event sample. The measurements are compared to the predictions of the PYTHIA 8 CUETM1 (long dashes), PYTHIA 8 MBR4C (continuous line), and epos LHC (short dashes) event generators. The band encompassing the data points represent the total systematic uncertainty, while the statistical uncertainty is included as a vertical bar for each data point. The lower panel shows the corresponding MC-to-data ratios.
Tables

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Table 1:
Summary of stable-particle level definitions for each of the event samples, corresponding to the inelastic, the NSD-enhanced, and SD-enhanced categories. Charged particles are selected with $ {p_{\mathrm {T}}} > $ 0.5 GeV and $ | \eta | < $ 2.4. Forward trigger particles correspond to those with energy $ E > $ 5 GeV located in side$^-$ (defined as $-5 < \eta < -3$) and/or side$^+$ (defined as 3 $ < \eta < 5$). Similarly, a {veto} corresponds to the absence of a trigger particle with $ E > $ 5 GeV in side$^-$ and/or side$^+$.

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Table 2:
Summary of systematic uncertainties per observable for each of the event samples. The observables are (presented as rows, from top to bottom) pseudorapidity, multiplicity, transverse momentum, leading transverse momentum, and the integral of the latter. The columns, from left to right, represent the following event samples: Inelastic, NSD-enhanced and SD-enhanced. For each observable the respective sources of uncertainty are listed. These are, from top to bottom: the tracking efficiency, the pileup modelling, the event selection and the model dependence. The final value in each case represents the total systematic uncertainty.
Summary
Charged particle distributions measured with the CMS detector in minimum bias proton-proton collisions at a center-of-mass energy of $\sqrt{s} = $ 13 TeV have been presented. Charged particles are selected with transverse momenta satisfying ${p_{\mathrm{T}}} > $ 0.5 GeV in the pseudorapidity range $|{\eta}| < $ 2.4. The measured distributions, corrected for detector effects, are presented for three different event samples selected according to the maximum particle energy in the range 3 $ < |{\eta}| < $ 5. The event samples correspond to an inelastic sample, a sample dominated by nonsingle diffractive dissociation events (NSD-enhanced sample), and an event sample enriched by single diffractive dissociation events (SD-enhanced sample).
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