$Υ$ production and nuclear modification at forward rapidity in Pb-Pb collisions at $\mathbf{\sqrt{\textit{s}_{\textbf{NN}}}=5.02}$ TeV

The production of $\Upsilon$ mesons in Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}$ = 5 TeV is measured with the muon spectrometer of ALICE at the LHC. The yields as well as the nuclear modification factors are determined in the forward rapidity region $2.5<~y<~4.0$, as a function of rapidity, transverse momentum and collision centrality. The results show that the production of $\Upsilon$(1S) is suppressed by a factor of about three with respect to the production in proton-proton collisions. For the first time, a significant $\Upsilon$(2S) signal is observed at forward rapidity, indicating a suppression stronger by about a factor 2-3 with respect to the ground state. The measurements are compared with transport, hydrodynamic, comover and statistical hadronisation model calculations.

 

Phys. Lett. B 822 (2021) 136579
HEP Data
e-Print: arXiv:2011.05758 | PDF | inSPIRE
CERN-EP-2020-207
Figure group

Figure 2

Acceptance and reconstruction efficiency (\Axe) for \upsones and \upstwos as a function of centrality (left) and rapidity (right). The vertical error bars denote the statistical uncertainties.

Figure 3

Rapidity (left) and \pt (right) differential measurements of normalised yields for inclusive $\Upsilon$~production in \PbPb collisions at \fivenn together with CMS measurements~. The \upstwos results are multiplied by a factor 4 for better visibility. The global uncertainties of the nuclear overlap functions and of the number of MB events are not represented.

Figure 4

Nuclear modification factor of \upsones and \upstwos as a function of the average number of participants. The filled boxes at unity correspond to the relative uncertainties correlated with centrality. The results are compared with calculations from the comover and the hydrodynamic models~ in the left panel and with the transport descriptions~ in the right panel

Figure 5

(Left) Ratio of \upstwos-to-\upsones yields as a function of the average number of participants. The results are displayed on top of the statistical hadronisation model values~. The two curves represent the uncertainty of the pp-like contribution of the corona of the nuclear overlap (Right) Relative nuclear modification factor along with the predictions from the comover interaction model~, hydrodynamic calculations~, from the transport model~ and calculations based on the coupled Boltzmann equations~. The filled red box at unity denotes the uncertainty on the \upstwos-to-\upsones cross section ratio in pp collisions

Figure 6

Nuclear modification factor of \upsones as a function of the transverse momentum. The red box at unity corresponds to the global uncertainty correlated with \pt Predictions from the hydrodynamic~ and transport~ models are also shown.

Figure 7

Nuclear modification factor of \upsones and \upstwos as a function of rapidity. The red and violet filled boxes at unity correspond to the global uncertainties common to both $\Upsilon$~states from the ALICE and CMS measurements. The experimental data are compared with hydrodynamic~ and coupled Boltzmann equations~ calculations on the left and right panel, respectively.