In-medium $\mathrm{{\rm Y}}$ suppression and feed-down in UU and PbPb collisions

The suppression of $\mathrm{{\rm Y}}$ mesons in the hot quark-gluon plasma (QGP) versus reduced feed-down is investigated in UU collisions at energies currently available at the BNL Relativistic Heavy Ion Collider and PbPb collisions at energies available at the CERN Large Hadron Collider. Our centrality- and $p_{\text{T}}$-dependent model encompasses screening, collisional damping, and gluodissociation in the QGP. For $\mathrm{{\rm Y}}\left(1S\right)$ it is in agreement with data from both STAR and CMS collaborations provided the relativistic Doppler effect and the reduced feed-down from the $\mathrm{{\rm Y}}\left(nS\right)$ and ${\chi }_{\mathrm{b}}\left(nP\right)$ states are properly considered. At both energies, most of the $\mathrm{{\rm Y}}\left(1S\right)$ suppression is found to be due to reduced feed-down, whereas most of the $\mathrm{{\rm Y}}\left(2S\right)$ suppression is caused by hot-medium effects. The importance of the latter increases with energy. The $p_{\text{T}}$ dependence is flat due to the relativistic Doppler effect and reduced feed-down. We predict the $\mathrm{{\rm Y}}\left(1S\right)$ suppression in PbPb at $\sqrt{s_{NN}}=5.02TeV$.

Figure 1

Transverse-momentum dependence of the ground-state suppression factor $R_{AA}^{}\left[\mathrm{{\rm Y}}\left(1S\right)\right]$ in minimum-bias PbPb collisions at $\sqrt{s_{NN}}=2.76TeV$ for effective temperatures based on maximum blue shift only $T_{\text{eff}}={max}_{\mathrm{\Omega }}\left(T_{\text{D}}\right)$ and angular-averaged temperature $T_{\text{eff}}={\langle T_{\text{D}}\rangle }_{\mathrm{\Omega }}$ in comparison with the unmodified case $T_{\text{eff}}\equiv T$. Preliminary data from CMS [8] at $2.76TeV$ are shown for comparison. Statistical error bars are solid; systematic ones, shaded.

Figure 2

Transverse-momentum dependence of the suppression factors $R_{AA}^{}\left[\mathrm{{\rm Y}}\left(1S\right)\right]$ for the ground state and $R_{AA}^{}\left[\mathrm{{\rm Y}}\left(2S\right)\right]$ for the first excited state in minimum-bias PbPb collisions at $\sqrt{s_{NN}}=2.76TeV$. The (upper) dashed curves show the suppression in the hot medium, the (lower) solid curves the suppression including reduced feed-down, which is only important for the ground state.

Figure 3

Transverse-momentum dependence of the suppression factors $R_{AA}^{\text{QGP}}$ (dashed line) and $R_{AA}^{}$ (solid line) for the ground state in minimum-bias PbPb collisions at $\sqrt{s_{NN}}=2.76TeV$ ($T_0=480MeV$) compared with recent CMS data [8]. Our predictions for $5.02TeV$ PbPb ($T_0=513MeV$) are shown as dotted and dash-dotted curves for $R_{AA}^{\text{QGP}}$ and $R_{AA}^{}$, respectively.

Figure 4

Calculated suppression factor for the $\mathrm{{\rm Y}}$ spin-triplet ground state $R_{AA}^{}\left[\mathrm{{\rm Y}}\left(1S\right)\right]$ in UU collisions at $\sqrt{s_{NN}}=193GeV$ (solid line) together with centrality-dependent preliminary data ($10--30\%$ and $0--10\%, \left|y\right|<1$ ) from STAR [4] as a function of the number of participants $N_{\text{part}}$ (averaged over centrality bins). The suppression factor $R_{AA}^{\text{QGP}}$ in the QGP phase without the effect of reduced feed-down is also shown.

Figure 5

Top: Calculated suppression factor $R_{AA}^{}\left[\mathrm{{\rm Y}}\left(1S\right)\right]$ in PbPb collisions at $\sqrt{s_{NN}}=2.76$ TeV (solid line) together with centrality-dependent data from CMS ($\left|y\right|<2.4$, [8]) and ALICE ($2.5<y<4$, [2]) as a function of the number of participants $N_{\text{part}}$ (averaged over centrality bins). The suppression factor $R_{AA}^{\text{QGP}}$ in the QGP phase without the effect of reduced feed-down is shown as a dashed (upper) curve. Bottom: Suppression factor for the first excited state $R_{AA}^{}\left[\mathrm{{\rm Y}}\left(2S\right)\right]$ in PbPb collisions at $\sqrt{s_{NN}}=2.76TeV$ (solid line) together with preliminary data from CMS [8]. The suppression factor $R_{AA}^{\text{QGP}}$ in the QGP-phase (dashed) accounts for most of the calculated total suppression (solid) for the $\mathrm{{\rm Y}}\left(2S\right)$.

Figure 6

Calculated suppression factor $R_{AA}^{}\left[\mathrm{{\rm Y}}\left(1S\right)\right]$ in PbPb collisions at $\sqrt{s_{NN}}=2.76TeV$ (lower solid line) and prediction at $5.02TeV$ (lower dash-dotted line) together with centrality-dependent $2.76TeV$ data from CMS ($\left|y\right|<2.4$, [8]) as function of the number of participants $N_{\text{part}}$ (averaged over centrality bins). The suppression factors $R_{AA}^{\text{QGP}}$ in the QGP phase without the effect of reduced feed-down are shown as upper curves (dashed and dotted) for both energies, again yielding slightly more suppression at the higher energy.