CMS-HIN-19-009 ; CERN-EP-2020-141 | ||
Studies of charm and beauty hadron long-range correlations in pp and pPb collisions at LHC energies | ||
CMS Collaboration | ||
15 September 2020 | ||
Phys. Lett. B 813 (2021) 136036 | ||
Abstract: Measurements of the second Fourier harmonic coefficient (v2) of the azimuthal distributions of prompt and nonprompt D0 mesons (the latter coming from beauty hadron decays) produced in pp and pPb collisions are presented. The data samples are collected by the CMS experiment at nucleon-nucleon center-of-mass energies of 13 and 8.16 TeV, respectively. In high multiplicity pp collisions, v2 signals for prompt charm hadrons are reported for the first time, and are found to be comparable to those for light-flavor hadron species over a transverse momentum (pT) range of 2-6 GeV. Compared at similar event multiplicities, the prompt D0 meson v2 values in pp and pPb collisions are similar in magnitude. The v2 values for open beauty hadrons are extracted for the first time via nonprompt D0 mesons in pPb collisions. For pT in the range of 2-5 GeV, the results suggest that v2 for nonprompt D0 mesons are smaller than those for prompt D0 mesons. These new measurements indicate a positive charm hadron v2 in pp collisions and suggest a mass dependence in v2 between charm and beauty hadrons in the pPb system. These results provide insights into the origin of heavy-flavor quark collectivity in small systems. | ||
Links: e-print arXiv:2009.07065 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
Example of fits to the invariant mass spectrum and VS+B2Δ(minv), for the BDT prompt-trained sample in pp collisions. |
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Figure 2:
Example of fits to the invariant mass spectrum and VS+B2Δ(minv), for the BDT nonprompt-trained sample in pPb collisions. The left plot shows the fit for DCA< 0.008 cm and the right plot is for 0.008 <DCA< 0.014 cm. |
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Figure 2-a:
Example of fit to the invariant mass spectrum and VS+B2Δ(minv), for the BDT nonprompt-trained sample in pPb collisions. The plot shows the fit for DCA< 0.008 cm. |
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Figure 2-b:
Example of fit to the invariant mass spectrum and VS+B2Δ(minv), for the BDT nonprompt-trained sample in pPb collisions. The plot shows the fit for 0.008 <DCA< 0.014 cm. |
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Figure 3:
Left: example of template fit to the D0 meson DCA distribution in the pT interval 3-4 GeV for events with 185 ≤Nofflinetrk< 250 of pPb collisions. Right: inclusive D0 VS2Δ values from the three DCA regions as a function of the corresponding nonprompt D0 fraction, for 2 <pT< 5 GeV and 5 <pT< 8 GeV. The red line is a linear fit to VS2Δ data. |
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Figure 3-a:
Example of template fit to the D0 meson DCA distribution in the pT interval 3-4 GeV for events with 185 ≤Nofflinetrk< 250 of pPb collisions. |
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Figure 3-b:
Inclusive D0 VS2Δ values from the three DCA regions as a function of the corresponding nonprompt D0 fraction, for 2 <pT< 5 GeV and 5 <pT< 8 GeV. The red line is a linear fit to VS2Δ data. |
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Figure 4:
Results of vsub2 for prompt D0 mesons, as a function of pT for |ylab|< 1, with Nofflinetrk≥ 100 in pp collisions at √s= 13 TeV. Published data for charged particles, K0S mesons and Λ baryons are also shown for comparison [19]. The vertical bars correspond to the statistical uncertainties, while the shaded areas denote the systematic uncertainties. The horizontal bars represent the width of the pT bins. |
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Figure 5:
Results of vsub2 for prompt D0 mesons, as a function of event multiplicity for three different pT ranges, with |ylab|< 1 in pp collisions at √s= 13 TeV and pPb collisions at √sNN= 8.16 TeV. The vertical bars correspond to statistical uncertainties, while the shaded areas denote the systematic uncertainties. The y-axis is zoomed in to better display the data; the uncertainties are symmetric with respect to their central values. The horizontal bars represent the width of the Nofflinetrk bins. The right-most points with right-hand arrows correspond to Nofflinetrk≥ 100 for pp collisions and Nofflinetrk≥ 250 for pPb collisions. The vsub2 values in pPb collisions with 185 ≤Nofflinetrk< 250 are measured in different pT ranges from Ref. [57] and are found to be consistent with Ref. [57]. |
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Figure 6:
Results of vsub2 for prompt and nonprompt D0 mesons, as well as K0S mesons, Λ baryons for |ylab|< 1, and prompt J/ψ mesons for 1.2 <|ylab|< 2.4, as functions of pT with 185 ≤Nofflinetrk< 250 in pPb collisions at √sNN= 8.16 TeV [57,59]. The vertical bars correspond to statistical uncertainties, while the shaded areas denote the systematic uncertainties. The horizontal bars represent the width of the nonprompt D0 pT bins. The dashed, dash-dotted, and solid lines, show the theoretical calculations of prompt D0, J/ψ, and nonprompt D0 mesons, respectively, within the CGC framework [61,77]. |
Tables | |
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Table 1:
Summary of systematic uncertainties on vsub2. The ranges of systematic uncertainties correspond to the pT ranges of D0 mesons. |
Summary |
The first measurements of elliptic azimuthal anisotropies for prompt D0 mesons in proton-proton (pp) collisions at center-of-mass energy √s= 13 TeV, and for nonprompt D0 mesons from beauty hadron decays in proton-lead (pPb) collisions at nucleon-nucleon center-of-mass energy √sNN= 8.16 TeV are presented. In pp collisions with multiplicities of Nofflinetrk≥100, the second Fourier harmonic coefficient (v2) of the azimuthal distributions for prompt D0 mesons are measured over the transverse momentum (pT) range of 2-8 GeV, with indications of positive v2 signals over the pT range of 2-4 GeV. These values are found to be comparable (or slightly smaller) to those of light-flavor hadron species. At similar event multiplicities, the prompt D0 meson v2 signals in pp and pPb collisions are found to be comparable in magnitude. The v2 values of open beauty hadrons are extracted for the first time via non-prompt D0 mesons in pPb collisions, with magnitudes smaller than those for prompt D0 mesons for pT∼2-5 GeV. The new measurements of charm hadron v2 in the pp system and the indications of mass dependence of heavy-flavor hadron v2 in the pPb system provide insights into the origin of heavy-flavor quark collectivity in small colliding systems. |
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Compact Muon Solenoid LHC, CERN |
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