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| CMS-HIN-21-001 ; CERN-EP-2023-164 | ||
| Study of azimuthal anisotropy of $ \Upsilon $(1S) mesons in pPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} $ = 8.16 TeV | ||
| CMS Collaboration | ||
| 5 October 2023 | ||
| Phys. Lett. B 850 (2024) 138518 | ||
| Abstract: The azimuthal anisotropy of $ \Upsilon $(1S) mesons in high-multiplicity proton-lead collisions is studied using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 8.16 TeV. The $ \Upsilon $(1S) mesons are reconstructed using their dimuon decay channel. The anisotropy is characterized by the second Fourier harmonic coefficients, found using a two-particle correlation technique, in which the $ \Upsilon $(1S) mesons are correlated with charged hadrons. A large pseudorapidity gap is used to suppress short-range correlations. Nonflow contamination from the dijet background is removed using a low-multiplicity subtraction method, and the results are presented as a function of $ \Upsilon $(1S) transverse momentum. The azimuthal anisotropies are smaller than those found for charmonia in proton-lead collisions at the same collision energy, but are consistent with values found for $ \Upsilon $(1S) mesons in lead-lead interactions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. | ||
| Links: e-print arXiv:2310.03233 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Result of a $ \chi^{2} $ fit of the first three terms ($ V_{1}, V_{2}, V_{3} $) of a Fourier series for a typical $ \Delta\phi $ projection from the high-multiplicity (70 $ \leq N^{\text{offline}}_{\text{trk}} < $ 300) two-dimensional $ \Upsilon $(1S)-track correlation plot. |
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Figure 2:
Simultaneous fit of the $ m_{\mu^{+}\mu^{-}} $ and $ V_{2} $ distributions for high-multiplicity (70 $ \leq N^{\text{offline}}_{\text{trk}} < $ 300) pPb events. The points indicate the event yields in the upper plot and $ V_{2} $ values from the Fourier component fit in the lower plot. The red solid (blue dash) lines correspond to the total (background) simultaneous fit to both distributions. |
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Figure 3:
The $ p_{\mathrm{T}} $ dependent $ v_{2}^{\text{sub}} $ values of $ \Upsilon $(1S) mesons measured in the high-multiplicity region 70 $ \leq N^{\text{offline}}_{\text{trk}} < $ 300, where a low-multiplicity region $ N^{\text{offline}}_{\text{trk}} < $ 50 is used to estimate and correct for the dijet contribution. (Left) The results are compared to the corresponding results from PbPb collisions at 5.02 TeV, measured within the 10-90% centrality range [50]. The integrated bin is 0-50 Gev/$c$ for PbPb. (Right) The same distribution is also compared with the $ v_{2}^{\text{sub}} $ values for prompt J$/\psi $ mesons within 1.4 $ < |\text{y}| < $ 2.4 in pPb collisions at 8.16 TeV for 180 $ \leq N^{\text{offline}}_{\text{trk}} < $ 250, where a low-multiplicity range with $ N^{\text{offline}}_{\text{trk}} < $ 35 was used to estimate and correct for the dijet contribution [47]. The vertical bars denote statistical uncertainties and the shaded boxes represent systematic uncertainties, while the widths of the boxes represent the $ p_{\mathrm{T}} $ bin ranges. |
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Figure 3-a:
The $ p_{\mathrm{T}} $ dependent $ v_{2}^{\text{sub}} $ values of $ \Upsilon $(1S) mesons measured in the high-multiplicity region 70 $ \leq N^{\text{offline}}_{\text{trk}} < $ 300, where a low-multiplicity region $ N^{\text{offline}}_{\text{trk}} < $ 50 is used to estimate and correct for the dijet contribution. The results are compared to the corresponding results from PbPb collisions at 5.02 TeV, measured within the 10-90% centrality range [50]. The integrated bin is 0-50 Gev/$c$ for PbPb. The vertical bars denote statistical uncertainties and the shaded boxes represent systematic uncertainties, while the widths of the boxes represent the $ p_{\mathrm{T}} $ bin ranges. |
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Figure 3-b:
The $ p_{\mathrm{T}} $ dependent $ v_{2}^{\text{sub}} $ values of $ \Upsilon $(1S) mesons measured in the high-multiplicity region 70 $ \leq N^{\text{offline}}_{\text{trk}} < $ 300, where a low-multiplicity region $ N^{\text{offline}}_{\text{trk}} < $ 50 is used to estimate and correct for the dijet contribution. The distribution is compared with the $ v_{2}^{\text{sub}} $ values for prompt J$/\psi $ mesons within 1.4 $ < |\text{y}| < $ 2.4 in pPb collisions at 8.16 TeV for 180 $ \leq N^{\text{offline}}_{\text{trk}} < $ 250, where a low-multiplicity range with $ N^{\text{offline}}_{\text{trk}} < $ 35 was used to estimate and correct for the dijet contribution [47]. The vertical bars denote statistical uncertainties and the shaded boxes represent systematic uncertainties, while the widths of the boxes represent the $ p_{\mathrm{T}} $ bin ranges. |
| Tables | |
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Table 1:
Absolute systematic uncertainties (10$^{-2} $) included in the measurement of $ v_{2}^{\text{sub}} $ evaluated in different $ p_{\mathrm{T}}^{\Upsilon{\textrm{(1S)}}} $ bins (in Gev/$c$). |
| Summary |
| The azimuthal anisotropy of $ \Upsilon $(1S) mesons, as quantified using the elliptic flow coefficients $ v_{2}^{\text{sub}} $, is measured as a function of transverse momentum for the first time in high-multiplicity proton-lead (pPb) collision events at the center-of-mass energy per nucleon pair of $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 8.16 TeV. The measurement is corrected for dijet background using a low-multiplicity subtraction method. The $ v_{2}^{\text{sub}} $ values are observed to be consistent with zero. These results are also consistent with those found previously in PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV. Comparing $ v_{2}^{\text{sub}} $ of $ \Upsilon $(1S) and those of J$/\psi $ mesons, the results suggest that any collectivity of bottomonia is smaller than that of charmonia in pPb collisions. The direct comparison of $ \Upsilon $(1S) flow results for pPb and PbPb reinforces the conclusion that there is no evidence for collective flow of bottom quarks in systems of any size. |
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