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| CMS-HIN-19-002 ; CERN-EP-2020-039 | ||
| Measurement of the azimuthal anisotropy of $\Upsilon(\mathrm{1S})$ and $\Upsilon(\mathrm{2S})$ mesons in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV | ||
| CMS Collaboration | ||
| 14 June 2020 | ||
| Phys. Lett. B 819 (2021) 136385 | ||
| Abstract: The second-order Fourier coefficients (${v_{2}} $) characterizing the azimuthal distribution of $\Upsilon(\mathrm{1S})$ and $\Upsilon(\mathrm{2S})$ mesons arising from PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV are studied. The $\Upsilon$ mesons are reconstructed in their dimuon decay channel, as measured by the CMS detector. The data set was collected in 2018 and corresponds to an integrated luminosity of 1.7 nb$^{-1}$. The scalar product method is used to extract the ${v_{2}} $ coefficients of the azimuthal distribution. Results are reported for the rapidity range $|y| < $ 2.4, with the transverse momentum 0 $ < {p_{\mathrm{T}}} < $ 50 GeV/$c$, and in three centrality ranges of 10-30, 30-50 and 50-90%. In contrast to the $\mathrm{J}/\psi$ mesons, no azimuthal anisotropy is observed for the $\Upsilon$ mesons. | ||
| Links: e-print arXiv:2006.07707 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Simultaneous fit of the dimuon invariant mass spectrum and the $ {v_{2}} ^{\mathrm {Sig+Bkg}}$ distribution, as defined in Eq. (4), for $ {p_{\mathrm {T}}} < $ 50 GeV/$c$ and with centrality 10-90%. The solid (signal + background) and dashed (background only) blue lines show the result of the mass fit, and the solid and dashed red lines show the corresponding results for the binned $\chi ^2$ fit to the ${v_{2}}$ distribution. |
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Figure 2:
(left) ${p_{\mathrm {T}}}$ integrated ${v_{2}}$ values for $\Upsilon(\mathrm{1S})$ mesons measured in four centrality bins and for the $\Upsilon(\mathrm{2S})$ meson in the 10-90% centrality range. (right) ${v_{2}}$ of $\Upsilon(\mathrm{1S})$ mesons as a function of ${p_{\mathrm {T}}}$ in the 10-90% centrality range compared with model calculations from Du and Rapp [22], Yao [42,43], Hong and Lee [44,45], and Bhaduri, Borghini, Jaiswal and Strickland [46]. All results are for the rapidity range of $ { | y |} < $ 2.4. The vertical bars denote statistical uncertainties, and the rectangular boxes show the total systematic uncertainties. |
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Figure 2-a:
${p_{\mathrm {T}}}$ integrated ${v_{2}}$ values for $\Upsilon(\mathrm{1S})$ mesons measured in four centrality bins and for the $\Upsilon(\mathrm{2S})$ meson in the 10-90% centrality range. All results are for the rapidity range of $ { | y |} < $ 2.4. The vertical bars denote statistical uncertainties, and the rectangular boxes show the total systematic uncertainties. |
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Figure 2-b:
${v_{2}}$ of $\Upsilon(\mathrm{1S})$ mesons as a function of ${p_{\mathrm {T}}}$ in the 10-90% centrality range compared with model calculations from Du and Rapp [22], Yao [42,43], Hong and Lee [44,45], and Bhaduri, Borghini, Jaiswal and Strickland [46]. All results are for the rapidity range of $ { | y |} < $ 2.4. The vertical bars denote statistical uncertainties, and the rectangular boxes show the total systematic uncertainties. |
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Figure 3:
The ${v_{2}}$ coefficients for $\Upsilon(\mathrm{1S})$ mesons as a function of ${p_{\mathrm {T}}}$ in three centrality bins: 10-30% (left), 30-50% (middle) and 50-90% (right). The rapidity range is $ { | y |} < $ 2.4. The vertical lines indicate the statistical uncertainties and the rectangular boxes show the total systematic uncertainties. |
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Figure 4:
The ${v_{2}}$ for $\Upsilon(\mathrm{1S})$ mesons as a function of ${p_{\mathrm {T}}}$ in the rapidity range $ { | y |} < $ 2.4 compared with the ALICE results for $\Upsilon(\mathrm{1S})$ (open circles) and $\mathrm{J}/\psi$ (full squares) mesons measured in 2.5 $ < y < $ 4 [24]. All results are measured in the range of 0 $ < {p_{\mathrm {T}}} < $ 15 GeV/$c$ and centrality interval 5-60%. The vertical bars denote statistical uncertainties, and the rectangular boxes show the total systematic uncertainties. |
| Summary |
| The ${v_{2}} $ coefficients for $\Upsilon(\mathrm{1S})$ and $\Upsilon(\mathrm{2S})$ mesons are measured in PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Results are reported for the rapidity range $|y| < $ 2.4, with transverse momentum 0 $ < {p_{\mathrm{T}}} < $ 50 GeV/$c$, and in three centrality intervals of 10-30, 30-50, and 50-90% for the $\Upsilon(\mathrm{1S})$ meson, while the centrality interval 10-90% is used for the $\Upsilon(\mathrm{2S})$ meson. The ${v_{2}} $ values are observed to be compatible with zero for the $\Upsilon(\mathrm{1S})$ meson in the measured kinematic bins and centrality intervals. This observation contrasts with the positive ${v_{2}} $ values reported for $\mathrm{J}/\psi$ mesons, suggesting different medium effects for charmonia and bottomonia. The measured values of ${v_{2}} $ are consistent with the predictions of several theoretical models. The ${v_{2}} $ value found for $\Upsilon(\mathrm{2S})$ mesons, which is being reported for the first time, is also consistent with zero. As there are expected to be differences in the various processes through which the QGP affects $\Upsilon(\mathrm{1S})$ and $\Upsilon(\mathrm{2S})$ mesons, these measurements provide new inputs for the study of bottomonia production in heavy ion collisions. |
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