Nuclear modification of $\Upsilon$ states in pPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV

The CMS collaboration
Phys.Lett.B 835 (2022) 137397, 2022.

Abstract (data abstract)
Production cross sections of $\Upsilon(1S)$, $\Upsilon(2S)$, and $\Upsilon(3S)$ states decaying into $\mu^{+}\mu^{-}$ in proton-lead (pPb) collisions are reported using data collected by the CMS experiment at $\sqrt{s_{_{\mathrm{NN}}}} = $ 5.02 TeV. A comparison is made with corresponding cross sections obtained with pp data measured at the same collision energy and scaled by the Pb nucleus mass number. The nuclear modification factor for $\Upsilon(1S)$ is found to be $R_{\mathrm{pPb}}(\Upsilon(1S)) = $ 0.806 $ \pm\ $ 0.024 (stat) $ \pm\ $ 0.059 (syst). Similar results for the excited states indicate a sequential suppression pattern, such that $R_{\mathrm{pPb}}(\Upsilon(1S)) > R_{\mathrm{pPb}}(\Upsilon(2S)) > R_{\mathrm{pPb}}(\Upsilon(3S))$. The suppression is much less pronounced in pPb than in PbPb collisions, and independent of transverse momentum $p^{\Upsilon}_{T}$ and center-of-mass rapidity $y^{\Upsilon}_{CM}$ of the individual $\Upsilon$ state in the studied range $p^{\Upsilon}_{T} < $ 30 GeV/c and $|y^{\Upsilon}_{CM}| < $ 1.93. Models that incorporate sequential suppression of bottomonia in pPb collisions are in better agreement with the data than those which only assume initial-state modifications.

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