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Suppression of $\Upsilon$ production in d+Au and Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV

The collaboration
Phys.Lett.B 735 (2014) 127-137, 2014.

Abstract
We report measurements of Upsilon meson production in p+p, d+Au, and Au+Au collisions using the STAR detector at RHIC. We compare the Upsilon yield to the measured cross section in p+p collisions in order to quantify any modifications of the yield in cold nuclear matter using d+Au data and in hot nuclear matter using Au+Au data separated into three centrality classes. Our p+p measurement is based on three times the statistics of our previous result. We obtain a nuclear modification factor for Upsilon(1S+2S+3S) in the rapidity range |y|<1 in d+Au collisions of R_dAu = 0.79 +/- 0.24 (stat.) +/- 0.03 (sys.) +/- 0.10 (pp sys.). A comparison with models including shadowing and initial state parton energy loss indicates the presence of additional cold-nuclear matter suppression. Similarly, in the top 10% most-central Au+Au collisions, we measure a nuclear modification factor of R_AA=0.49 +/- 0.1 (stat.) +/- 0.02 (sys.) +/- 0.06 (pp sys.), which is a larger suppression factor than that seen in cold nuclear matter. Our results are consistent with complete suppression of excited-state Upsilon mesons in Au+Au collisions. The additional suppression in Au+Au is consistent with the level expected in model calculations that include the presence of a hot, deconfined Quark-Gluon Plasma. However, understanding the suppression seen in d+Au is still needed before any definitive statements about the nature of the suppression in Au+Au can be made.

• Table 1

Figure 1a

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Invariant mass distributions of electron pairs in the region $|y_{ee}| < 0.5$, p+p.

• Table 2

Figure 1b

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Invariant mass distributions of electron pairs in the region $|y_{ee}| < 0.5$, d+Au.

• Table 3

Figure 2a

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(a) $B_{ee} \times d\sigma/dy$ vs. $y$ for p+p collisions and for d+Au collisions (scaled down by 103).

• Table 4

Figure 2b

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$R_{dAu}$ vs. $y$.

• Table 5

Figure 3a

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Comparison of our d+Au measurements to the pA measurements from E772. Ratio of $\Upsilon$ production in pA to pp scaled...

• Table 6

Figure 3b

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Comparison of our d+Au measurements to the pA measurements from E772. Exponent $\alpha$ as a function of $x_{F}$.

• Table 7

Figure 4a

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Invariant mass distributions of electron pairs in the region $|y_{ee}| < 1.0$ for the centrality selections $30-60\%$.

• Table 8

Figure 4b

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Invariant mass distributions of electron pairs in the region $|y_{ee}| < 1.0$ for the centrality selections $10-30\%$.

• Table 9

Figure 4c

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Invariant mass distributions of electron pairs in the region $|y_{ee}| < 1.0$ for the centrality selections $0-10\%$.

• Table 10

Figure 5a

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Nuclear modification factor for $\Upsilon$(1S+2S+3S), in $|y| < 1.0$ in d+Au and Au+Au collisions as a function of $N_{part}$.

• Table 11

Figure 5b

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Nuclear modification factor for $\Upsilon$(1S+2S+3S), in $|y| < 0.5$, in d+Au and Au+Au collisions as a function of $N_{part}$.

• Table 12

Figure 5c

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Nuclear modification factor for $\Upsilon$(1S) in $|y| < 1.0$, in d+Au and Au+Au collisions as a function of $N_{part}$.

• Table 13

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Nuclear modification factor for $\Upsilon$(1S) in $|y| < 0.5$, in d+Au and Au+Au collisions as a function of $N_{part}$.

• Table 14

Figure 6

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Nuclear modification factor of quarkonium states as a function of binding energy as measured by STAR.