Production of inclusive $Υ$(1S) and $Υ$(2S) in p-Pb collisions at $\mathbf{\sqrt{s_{\rm NN}} = 5.02}$ TeV

We report on the production of inclusive $\Upsilon$(1S) and $\Upsilon$(2S) in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV at the LHC. The measurement is performed with the ALICE detector at backward ($-4.46< y_{{\rm cms}}<-2.96$) and forward ($2.03< y_{{\rm cms}}<3.53$) rapidity down to zero transverse momentum. The production cross sections of the $\Upsilon$(1S) and $\Upsilon$(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of $\Upsilon$(1S). A suppression of the inclusive $\Upsilon$(1S) yield in p-Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon-nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.

Figures

Figure 1

Invariant mass distribution of opposite-sign dimuons in the rapidity regions $-4.46 < y_{\rm cms} < -2.96$ (top) and $2.03 < y_{\rm cms} < 3.53$ (bottom) in p-Pb collisions. In each case, the full curve shows the total fit function and the dashed curves the signal component for the three $\Upsilon$ states (see text for details).
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Figure 2

Inclusive $\Upsilon$(1S) production cross section as a function of rapidity in p-Pb collisions at $\snn=5.02$ TeV. The vertical error bars represent the statistical uncertainties and the open boxes the uncorrelated systematic uncertainties. The correlated systematic uncertainty is directly quoted in the figure. It is obtained by summing in quadrature the correlated uncertainty on the integrated luminosity and the uncertainty on the branching ratio of $\Upsilon$(1S) to dimuon. The bands correspond to the inclusive $\Upsilon$(1S) pp cross section obtained with the procedure described in the text and scaled by $A_{\mathrm{Pb}}$.
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Figure 3

Nuclear modification factor of inclusive $\Upsilon$(1S) in p-Pb collisions at $\snn=5.02$ TeV. The results are compared to those for inclusive J/$\psi$. The vertical error bars represent the statistical uncertainties and the open boxes the uncorrelated systematic uncertainties (for the J/$\psi$, the uncorrelated and partially correlated uncertainties have been added in quadrature). The full boxes around $R_{\rm pPb}=1$ show the size of the correlated uncertainties, which in the case of the $\Upsilon$ include only the correlated uncertainty on the luminosity (see Table 1).
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Figure 4

Nuclear modification factor of inclusive $\Upsilon$(1S) in p-Pb collisions at $\snn=5.02$ TeV as a function of rapidity. The vertical error bars represent the statistical uncertainties and the open boxes the uncorrelated systematic uncertainties. The full boxes around $R_{\rm pPb}=1$ show the size of the correlated uncertainties. Also shown are several model calculations:
(top) parton energy loss with and without EPS09 shadowing at NLO and CEM with EPS09 shadowing at NLO;
(bottom) CGC based and CSM with EPS09 shadowing at LO. For the latter the effect of variation in the shadowing and EMC curves is highlighted as described in the text.
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Figure 5

(Top) Forward-to-backward ratio $R_{\rm FB}$ of inclusive $\Upsilon$(1S) yields compared to the J/$\psi$ $R_{\rm FB}$. The vertical error bars represent the statistical uncertainties and the open boxes the uncorrelated systematic uncertainties.
(Bottom) Inclusive $\Upsilon$(1S) $R_{\rm FB}$ compared to theoretical model calculations. The statistical and systematic uncertainties for the experimental value are added in quadrature. For the calculations, uncertainties are quoted when available.
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