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| CMS-PAS-HIN-21-001 | ||
| Azimuthal anisotropy of $ \Upsilon$(1S) mesons in pPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 8.16 TeV | ||
| CMS Collaboration | ||
| April 2022 | ||
| Abstract: The azimuthal anisotropy of $ \Upsilon$(1S) mesons in high-multiplicity proton-lead (pPb) collisions is studied using data collected by the CMS experiment at a center-of-mass energy per nucleon pair of ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 8.16 TeV. The $ \Upsilon$(1S) mesons are reconstructed from the dimuon decay channel. The anisotropy, characterized by the second Fourier harmonic $v_{2}$ coefficient, is determined using the two-particle correlation technique, where the $ \Upsilon$(1S) mesons are correlated with charged hadrons. A large pseudorapidity gap is used to suppress short-range correlations. The $v_{2}$ values are measured in four transverse momentum intervals in the range from 0 to 30 GeV/$c$. No azimuthal anisotropy is observed for the $ \Upsilon$(1S) mesons in high-multiplicity pPb collisions, which is consistent with previous lead-lead collision results. | ||
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These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here. |
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| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Fitting of the first three terms of a Fourier series on the $\Delta \phi $ projection of $ \Upsilon$(1S)-track correlation in the high-multiplicity region of 70 $ \leq {N^{\text {offline}}_{\text {trk}}} < $ 300. |
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Figure 2:
Simultaneous fitting between the $ \Upsilon$(1S) invariant mass and $V_{2}$ distributions for high-multiplicity (70 $ \leq {N^{\text {offline}}_{\text {trk}}} < $ 300) pPb events. The points are yield for top plot and $V_{2}$ from the Fourier fit for bottom. The red (blue) lines correspond to a total (background) simultaneous fit to both distributions. |
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Figure 3:
The $v_{2}^{\text{sub}}$ of $ \Upsilon$(1S) mesons as a function of di-muon $ {p_{\mathrm {T}}} $ in the high-multiplicity region of 70 $ \leq {N^{\text {offline}}_{\text {trk}}} < $ 300 ($ {N^{\text {offline}}_{\text {trk}}} < $ 50 sub.). The vertical bars denote statistical uncertainties and the rectangular boxes systematic uncertainties. |
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Figure 4:
(Left) The $v_{2}^{\text{sub}}$ $ \Upsilon$(1S) mesons in Fig. 3 is compared with the one measured in PbPb collisions at 5.02 TeV within the 10-90% centrality range [39]. (Right) The same distribution is also compared with the $v_{2}^{\text{sub}}$ of prompt J/$\psi$ mesons within $|y_{lab}| < $ 1.4 in pPb collisions at 8.16 TeV for 180 $ \leq {N^{\text {offline}}_{\text {trk}}} < $ 250 (with a low-multiplicity range for subtraction $ {N^{\text {offline}}_{\text {trk}}} < $ 35) [38]. The vertical bars denote statistical uncertainties and the rectangular boxes systematic uncertainties, while the widths of the boxes represent the $ {p_{\mathrm {T}}} $ bins. |
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Figure 4-a:
(Left) The $v_{2}^{\text{sub}}$ $ \Upsilon$(1S) mesons in Fig. 3 is compared with the one measured in PbPb collisions at 5.02 TeV within the 10-90% centrality range [39]. (Right) The same distribution is also compared with the $v_{2}^{\text{sub}}$ of prompt J/$\psi$ mesons within $|y_{lab}| < $ 1.4 in pPb collisions at 8.16 TeV for 180 $ \leq {N^{\text {offline}}_{\text {trk}}} < $ 250 (with a low-multiplicity range for subtraction $ {N^{\text {offline}}_{\text {trk}}} < $ 35) [38]. The vertical bars denote statistical uncertainties and the rectangular boxes systematic uncertainties, while the widths of the boxes represent the $ {p_{\mathrm {T}}} $ bins. |
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Figure 4-b:
(Left) The $v_{2}^{\text{sub}}$ $ \Upsilon$(1S) mesons in Fig. 3 is compared with the one measured in PbPb collisions at 5.02 TeV within the 10-90% centrality range [39]. (Right) The same distribution is also compared with the $v_{2}^{\text{sub}}$ of prompt J/$\psi$ mesons within $|y_{lab}| < $ 1.4 in pPb collisions at 8.16 TeV for 180 $ \leq {N^{\text {offline}}_{\text {trk}}} < $ 250 (with a low-multiplicity range for subtraction $ {N^{\text {offline}}_{\text {trk}}} < $ 35) [38]. The vertical bars denote statistical uncertainties and the rectangular boxes systematic uncertainties, while the widths of the boxes represent the $ {p_{\mathrm {T}}} $ bins. |
| Tables | |
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Table 1:
Systematic uncertainties for dominant sources considered in $v_{2}^{\text{sub}}$ over the different $ {p_{\mathrm {T}}} $ bins. |
| Summary |
| The azimuthal anisotropy of $ \Upsilon$(1S) mesons, as expressed in terms of dijet corrected elliptic flow $v_{2}^{\text{sub}}$ coefficients, is measured as a function of transverse momentum ${p_{\mathrm{T}}}$ in high-multiplicity proton-lead (pPb) collision events at a center-of-mass energy per nucleon pair of ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 8.16 TeV. Results are reported for transverse momenta 0 $ < {p_{\mathrm{T}}} < $ 30 GeV/$c$ . The $v_{2}^{\text{sub}}$ values are observed to be consistent with zero within uncertainties in the measured kinematic ranges. These results are consistent with previous PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV. Comparing the $v_{2}^{\text{sub}}$ values of $ \Upsilon$(1S) and J/$\psi$ mesons in the same collision system, the result suggests that any medium effect on bottomonia is similar or smaller than that of charmonia in pPb collisions. As this analysis presents the first measurement of $ \Upsilon$(1S) meson azimuthal anisotropy in the pPb system, it provides an additional constraint on the study of bottomonia production in small systems. |
| Additional Figures | |
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Additional Figure 1:
$ v_{2}^{sub} $ values for $ \Upsilon$(1S) mesons as a function of $ p_{\mathrm{T}} $ in the high-multiplicity region of 70 $ \leq N_{\textrm{trk}}^{\textrm{offline}} < $ 300 ($ N_{\textrm{trk}}^{\textrm{offline}} < $ 50 subtracted). The vertical bars and rectangular boxes represent the statistical and systematic uncertainties, respectively. The yellow band represents the calculation based on Ref. [52], which incorporates the thermal widths to lower temperatures in pPb collisions using the medium profile obtained by hydrodynamical simulations. The 0-5% refers to the interval of the high-multiplicity events in the simulation. |
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Additional Figure 2:
The $ v_{2}^{sub} $ values for $ \Upsilon$(1S) mesons (purple cross) as a function of $ p_{\mathrm{T}} $ in the high-multiplicity region of 70 $ \leq N_{\textrm{trk}}^{\textrm{offline}} < $ 300 ($ N_{\textrm{trk}}^{\textrm{offline}} < $ 50 subtracted) compared to those of charged hadrons (gray band) [53], $ \textrm{K}^{0}_{\textrm{S}} $ (orange triangle) [54], $ \mathrm{J}/\psi $ (blue circle) [38], and prompt (green square) and non-prompt D$^{0}$ (brown star) [31]. Except for the $ \Upsilon$(1S) meson, the high-multiplicity region ranges in 185 $ \leq N_{\textrm{trk}}^{\textrm{offline}} < $ 250. The low-multiplicity ranges for subtraction is $ N_{\textrm{trk}}^{\textrm{offline}} < $ 35 for $ \textrm{K}^{0}_{\textrm{S}} $, $ \mathrm{J}/\psi $, and prompt/nonprompt D$^{0}$ while the charged hadrons are analyzed with the scalar product method. The vertical bars and the rectangular boxes represent the statistical and systematical uncertainties, respectively. |
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