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CMS-HIN-21-001 ; CERN-EP-2023-164
Study of azimuthal anisotropy of Υ(1S) mesons in pPb collisions at sNN = 8.16 TeV
Phys. Lett. B 850 (2024) 138518
Abstract: The azimuthal anisotropy of Υ(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 Υ(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 Υ(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 Υ(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 Υ(1S) mesons in lead-lead interactions at a nucleon-nucleon center-of-mass energy of 5.02 TeV.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Result of a χ2 fit of the first three terms (V1,V2,V3) of a Fourier series for a typical Δϕ projection from the high-multiplicity (70 Nofflinetrk< 300) two-dimensional Υ(1S)-track correlation plot.

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Figure 2:
Simultaneous fit of the mμ+μ and V2 distributions for high-multiplicity (70 Nofflinetrk< 300) pPb events. The points indicate the event yields in the upper plot and V2 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 pT dependent vsub2 values of Υ(1S) mesons measured in the high-multiplicity region 70 Nofflinetrk< 300, where a low-multiplicity region Nofflinetrk< 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 vsub2 values for prompt J/ψ mesons within 1.4 <|y|< 2.4 in pPb collisions at 8.16 TeV for 180 Nofflinetrk< 250, where a low-multiplicity range with Nofflinetrk< 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 pT bin ranges.

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Figure 3-a:
The pT dependent vsub2 values of Υ(1S) mesons measured in the high-multiplicity region 70 Nofflinetrk< 300, where a low-multiplicity region Nofflinetrk< 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 pT bin ranges.

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Figure 3-b:
The pT dependent vsub2 values of Υ(1S) mesons measured in the high-multiplicity region 70 Nofflinetrk< 300, where a low-multiplicity region Nofflinetrk< 50 is used to estimate and correct for the dijet contribution. The distribution is compared with the vsub2 values for prompt J/ψ mesons within 1.4 <|y|< 2.4 in pPb collisions at 8.16 TeV for 180 Nofflinetrk< 250, where a low-multiplicity range with Nofflinetrk< 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 pT bin ranges.
Tables

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Table 1:
Absolute systematic uncertainties (102) included in the measurement of vsub2 evaluated in different pΥ(1S)T bins (in Gev/c).
Summary
The azimuthal anisotropy of Υ(1S) mesons, as quantified using the elliptic flow coefficients vsub2, 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 sNN= 8.16 TeV. The measurement is corrected for dijet background using a low-multiplicity subtraction method. The vsub2 values are observed to be consistent with zero. These results are also consistent with those found previously in PbPb collisions at sNN= 5.02 TeV. Comparing vsub2 of Υ(1S) and those of J/ψ mesons, the results suggest that any collectivity of bottomonia is smaller than that of charmonia in pPb collisions. The direct comparison of Υ(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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