arXiv 1906.053752019-06-12nucl-thnucl-ex

$γp $反应中具有隐魅的核子共振

Nucleon Resonances with Hidden Charm in $γp $ reactions

Jia-Jun Wu, T. -S. H. Lee, Bing-Song Zou

备注：: 23 pages, 10 figures
发表信息：: Phys. Rev. C 100, 035206 (2019)
DOI：: 10.1103/PhysRevC.100.035206

摘要：

利用现有的介子-重子耦合道模型的预言，研究了$γp$反应中核子隐魅共振态$N^*_{c\bar{c}}$的激发。对于$γ\,p\rightarrow J/ψ\, p$过程，我们首先计算Pomeron交换振幅的参数确定从拟合可用的总截面数据不变的质量$W=300$ GeV。然后，我们添加的共振振幅，以检查在近阈值能量区域的$γ\,p\rightarrow J/ψ\, p$的横截面上的$ N^*_{c\bar{c}}$激发的影响。$N^*_{c\bar{c}}\to MB$跃迁矩阵元由介子-重子耦合通道模型预测的部分衰变宽度确定。用矢量介子占优（VMD）模型计算了$γp \to N^*_{c\bar{c}}$跃迁振幅。总的$γp\rightarrow J/ψ\, p$振幅则取决于离壳形状因子，参数为$F_V(q^2)=Λ^4/(Λ^4 + (q^2 - m^2_V)^2)$和$Λ=550$ MeV。然后，我们证明，$N^*_{c\bar{c}}$可以最容易地确定在大角度的外出$J/ψ$的贡献从坡密子交换的微分截面中变得可以忽略不计。在相同的VMD模型和$N^*_{c\bar{c}}$的耦合沟道模型下，我们还计算了$γ\,p\rightarrow Vp\rightarrow N^*_{c\bar{c}} \rightarrow \bar{D}^0Λ_c^+ (\bar{D}^{*0}Λ_c^+)$过程的共振振幅。通过加入由于$\bar{D}^{*0}$（$\bar{D}^{0})$）交换引起的非共振振幅，我们预测了$γ\,p\rightarrow \bar{D}^0Λ_c^+(\bar{D}^{*0}Λ^+_c)$的截面，为现有的$N^*_{c\bar{c}}$的介子-重子耦合通道模型的实验检验提供了依据.

英文摘要：

The excitations of nucleon resonances with hidden charm, $N^*_{c\bar{c}}$, in the $γp$ reactions are investigated by using the predictions from the available meson-baryons (MB) coupled-channel models. For the $γ\,p\rightarrow J/ψ\, p$ process, we first calculate the Pomeron-exchange amplitudes with the parameters determined from fitting the available total cross section data up to invariant mass $W=300$ GeV. We then add the resonant amplitudes to examine the effects of $ N^*_{c\bar{c}}$ excitations on the cross sections of $γ\,p\rightarrow J/ψ\, p$ in the near threshold energy region. The $N^*_{c\bar{c}}\to MB$ transition matrix elements are determined from the partial decay widths predicted by the meson-baryons coupled-channel models. The $γp \to N^*_{c\bar{c}}$ transition amplitudes are calculated from the Vector Meson Dominance (VMD) model. The total $γp\rightarrow J/ψ\, p$ amplitudes then depend on an off-shell form factor, parameterized as $F_V(q^2)=Λ^4/(Λ^4 + (q^2 - m^2_V)^2)$ with $Λ=550$ MeV. We then demonstrate that the $N^*_{c\bar{c}}$ can be most easily identified in the differential cross sections at large angles of outgoing $J/ψ$ where the contribution from Pomeron-exchange becomes negligible. With the same VMD model and the same coupled-channel models of $N^*_{c\bar{c}}$, we also calculate the resonant amplitudes for the $γ\,p\rightarrow Vp\rightarrow N^*_{c\bar{c}} \rightarrow \bar{D}^0Λ_c^+ (\bar{D}^{*0}Λ_c^+)$ processes. By adding the non-resonant amplitudes due to the exchange of $\bar{D}^{*0}$ ($\bar{D}^{0})$, we then predict the cross sections of $γ\,p\rightarrow \bar{D}^0Λ_c^+(\bar{D}^{*0}Λ^+_c)$ for additional experimental tests of the available meson-baryon coupled-channel models of $N^*_{c\bar{c}}$.

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