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arXiv 1407.7451nucl-ex
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p-Pb与ALICE碰撞中Psi(2S)的产生

Inclusive Psi(2S) production in p-Pb collisions with ALICE

Roberta Arnaldi

摘要:

ALICE合作研究了在欧洲核子研究中心大型强子对撞机上,在$\sqrt{s_{\rm NN}} = 5.02$ TeV的p-Pb碰撞中产生的包容性$ψ(\rm 2S)$。在$μ^{+}μ^{-}$衰变通道中,在前向(2.03 $<y_{\rm cms}<$ 3.53)和后向(-4.46 $<y_{\rm cms}<$ -2.96)质心快度范围内进行测量,作为横向动量或事件活动的函数。通过在p-Pb和pp碰撞中评估的截面之间的双倍比率$[σ_{ψ(\rm 2S)}/σ_{\rm J/ψ}]_{\rm pPb}/[σ_{ψ(\rm 2S)}/σ_{\rm J/ψ}]_{\rm pp}$以及通过计算$\rm J/ψ$和$ψ(\rm 2S)$核修饰因子,将$ψ(\rm 2S)$的产生与$\rm J/ψ$的产生进行比较。结果表明,相对于pp,$ψ(\rm 2S)$的产生受到抑制,特别是在后向快度区,抑制比$\rm J/ψ$强。$\rm J/ψ$和$ψ(\rm 2S)$行为之间的这种意想不到的差异,没有被基于核部分子阴影和相干能量损失机制的理论模型所解释,表明$ψ(\rm 2S)$生产上存在相当大的终态效应。

英文摘要:

The ALICE Collaboration has studied the inclusive $ψ(\rm 2S)$ production in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at the CERN LHC. Measurements are performed, in the $μ^{+}μ^{-}$ decay channel, in a forward (2.03$<y_{\rm cms}<$3.53) and in a backward (-4.46$<y_{\rm cms}<$-2.96) centre of mass rapidity ranges, as a function of transverse momentum or event activity. The $ψ(\rm 2S)$ production is compared to the $\rm J/ψ$ one through the double ratio $[σ_{ψ(\rm 2S)}/σ_{\rm J/ψ}]_{\rm pPb}/[σ_{ψ(\rm 2S)}/σ_{\rm J/ψ}]_{\rm pp}$ between the cross sections evaluated in p-Pb and pp collisions and by calculating the $\rm J/ψ$ and $ψ(\rm 2S)$ nuclear modification factors. Results indicate that the $ψ(\rm 2S)$ production is suppressed with respect to pp and, in particular in the backward rapidity region, the suppression is stronger than the $\rm J/ψ$ one. This unexpected difference between the $\rm J/ψ$ and $ψ(\rm 2S)$ behaviour, not accounted for by theoretical models based on nuclear parton shadowing and coherent energy loss mechanisms, indicates the presence of sizeable final state effects on the $ψ(\rm 2S)$ production.

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