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arXiv 1509.08802nucl-ex
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在$\sqrt{s_{\rm NN}}$ = 2.76 TeV的Pb-Pb碰撞中在非常低的PDMATHAAB下J/ $ψ$产额的过量测量

Measurement of an excess in the yield of J/$ψ$ at very low $p_{\rm T}$ in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

ALICE Collaboration

备注：
18 pages, 3 captioned figures, 1 table, authors from page 13, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/1918
发表信息：
Phys. Rev. Lett. 116 (2016) 222301
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摘要：

我们报告的第一次测量的J/ $ψ$在非常低的横向动量（$p_{\rm T}< 0.3$ GeV/ $c$）在外围强子碰撞在$\sqrt{s_{\rm NN}}$ = 2.76 TeV的铅铅，ALICE在欧洲核子研究中心的LHC进行。值得注意的是，在快度范围$2.5<y<4$中，J/ $ψ$的测量核修改因子在$p_{\rm T}$范围0-0.3 GeV/ $c$中在70-90%（50-70%）中心性类中达到约7（2）。在J/$ψ$的相干光生是其物理机制的假设下，得到了与所观察到的过量有关的J/$ψ$产生截面。如果得到证实，J/ $ψ$相干光生在铅铅碰撞的影响参数小于两倍的核半径的观察开辟了新的理论和实验的挑战和机遇。特别是伴随强子碰撞的相干光生现象，不仅可以为研究光生和核反应的动力学提供新的视角，而且也将成为研究夸克-胶子等离子体的新的探针。

英文摘要：

We report on the first measurement of an excess in the yield of J/$ψ$ at very low transverse momentum ($p_{\rm T}< 0.3$ GeV/$c$) in peripheral hadronic Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J/$ψ$ in the rapidity range $2.5<y<4$ reaches about 7 (2) in the $p_{\rm T}$ range 0-0.3 GeV/$c$ in the 70-90% (50-70%) centrality class. The J/$ψ$ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J/$ψ$ is the underlying physics mechanism. If confirmed, the observation of J/$ψ$ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nuclear radius opens new theoretical and experimental challenges and opportunities. In particular, coherent photoproduction accompanying hadronic collisions may provide insight into the dynamics of photoproduction and nuclear reactions, as well as become a novel probe of the Quark-Gluon Plasma.

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