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arXiv 2409.10364hep-ph
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阈值附近的$J/ψ$光生过程与隐粲五夸克态的信号

$J/ψ$ photoproduction near threshold and signals for the hidden charm pentaquarks

Ming-Xiao Duan, Chang Gong, Lin Qiu, Qiang Zhao

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10 pages, 6 figures
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AI总结：

本研究通过分析阈值附近$J/ψ$光生过程，结合坡密子交换模型与开粲道、$P_c$五夸克态效应，解释了GlueX实验的截面结构，并提出利用极化束流不对称性检验相关机制的实验方向。

摘要：

我们研究阈值附近的$J/ψ$光生过程$\boldsymbol{\to J/ψp}$，以探究开粲道的作用以及来自隐粲$P_c$五夸克态的可能信号。通过从高能区外推到低能区的坡密子交换模型描述衍射机制，结果表明，与GlueX合作组的最新结果相比，微分散射截面在大散射角处存在明显的偏差。纳入开粲道和中间$P_c$态能显著改善对微分散射截面数据的描述，尤其是在$\boldsymbol{\bar{D}^{(*)}}$阈值对应的能区。这可以将GlueX合作组在$\boldsymbol{\bar{D}^{(*)}}$阈值处观测到的结构解释为开粲CUSP效应。鉴于这些$P_c$五夸克态是由$\boldsymbol{\bar{D}^{(*)}}$动力学生成的强子分子态，我们发现这些$P_c$态的产生在领头阶应受到抑制，因为它们与$γp$和$J/ψp$的耦合均通过圈跃迁实现。这可以解释为何现有数据集未观测到明显的$P_c$态信号。为进一步厘清s道机制的作用，我们还研究了极化束流不对称性，该物理量对开粲阈值效应和$P_c$产生的干涉表现出敏感性。我们强烈建议在杰斐逊实验室对该可观测量进行实验测量。

英文摘要：

We study the $J/ψ$ photoproduction $γp\to J/ψp$ near threshold to investigate the role played by the open charm channels and possible signals from the hidden charm $P_c$ pentaquark states. With the diffractive mechanism described by a Pomeron exchange model extrapolated from high energies to the lower energy region, it shows that the differential cross sections compared with the recent results from the GlueX Collaboration have apparent deficits in the large scattering angles. The inclusion of the open charm channels and intermediate $P_c$ states can significantly improve the descriptions of the differential cross section data, in particular, at the energy regions of the $Λ_c\bar{D}^{(*)}$ thresholds. This can explain the structures observed by the GlueX Collaboration at the $Λ_c\bar{D}^{(*)}$ thresholds as the open charm CUSP effects. Given that these $P_c$ pentaquark states are hadronic molecules dynamically generated by the $Σ_c\bar{D}^{(*)}$, we find that the production of these $P_c$ states should be suppressed at leading order since their couplings to both $γp$ and $J/ψp$ are through loop transitions. This can explain why no obvious signals for the $P_c$ states are observed by the present datasets. In order to further disentangling the role played by $s$-channel mechanisms, we also investigate the polarized beam asymmetry which shows sensitivities to the open charm threshold effects and interferences from the $P_c$ productions. Experimental measurement of this observable at the Jefferson Laboratory is strongly encouraged.

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