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arXiv 2403.08342hep-phhep-exnucl-ex
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原子核深度非弹性散射中衍射的抑制与领头扭度核遮蔽的动力学机制

Suppression of diffraction in deep-inelastic scattering on nuclei and dynamical mechanism of leading twist nuclear shadowing

V. Guzey, M. Strikman

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15 pages, 8 figures. Final version matching the published one
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AI总结：

本研究采用领头扭度方法计算核深度非弹性散射的相关比值，揭示其与胶子饱和框架预测的差异，阐明核遮蔽的动力学机制及黑盘极限、饱和标度的相关规律。

摘要：

我们采用核遮蔽的领头扭度方法（LTA，leading twist approach），针对重核（Pb）与质子的相干及求和（相干加准弹性）核深度非弹性散射，计算了衍射部分子分布与普通部分子分布的比值$R_{A/p}=(f_{i/A}^{D(3)}/f_{i/A})/(f_{i/p}^{D(3)}/f_{i/p})$。研究发现，在宽范围的$x$（包括电子-离子对撞机的运动学区间）内，夸克对应的$R_{A/p}$约为0.5-1，衍射截面与总截面的比值$[(dσ_{\rm diff}/dM_X^2)/σ_{\rm tot}]_{eA}/[(dσ_{\rm diff}/dM_X^2)/σ_{\rm tot}]_{ep}$也符合该范围，胶子对应的$R_{A/p}$约为0.5-1.3，这再次印证了其与胶子饱和框架预测的$R_{A/p}$核增强效应存在差异。我们证明$R_{A/p}$的大小由虚光子的强子涨落与靶核子的相互作用截面控制，这解释了色偶极模型中$R_{A/p}$的增强效应及LTA中的抑制效应。我们指出，黑盘极限下求和散射与相干散射的$R_{A/p}$分别对应1和$R^{\rm coh}_{A/p}=0.86$。基于饱和标度的直观定义，我们表明在小碰撞参数$b$下，由于强领头扭度核遮蔽效应及核密度的稀疏性，重核与质子的饱和标度比值$Q_{sA}^2(b)/Q_{sp}^2(b) \approx 1$。

英文摘要：

Using the leading twist approach (LTA) to nuclear shadowing, we calculate the ratios of diffractive and usual parton distributions for a heavy nucleus (Pb) and the proton, $R_{A/p}=(f_{i/A}^{D(3)}/f_{i/A})/(f_{i/p}^{D(3)}/f_{i/p})$, for coherent and summed (coherent plus quasi-elastic) nuclear deep-inelastic scattering. We find that $R_{A/p} \approx 0.5-1$ for quarks as well as for the ratio of the diffractive and total cross sections $[(dσ_{\rm diff}/dM_X^2)/σ_{\rm tot}]_{eA}/[(dσ_{\rm diff}/dM_X^2)/σ_{\rm tot}]_{ep}$ and $R_{A/p} \approx 0.5-1.3$ for gluons in a broad range of $x$, including the kinematics of the Electron-Ion Collider, which reaffirms the difference from the nuclear enhancement of $R_{A/p}$ predicted in the gluon saturation framework. We demonstrate that the magnitude of $R_{A/p}$ is controlled by the cross section of the interaction of hadronic fluctuations of the virtual photon with target nucleons, which explains an enhancement of $R_{A/p}$ in the color dipole model and its suppression in LTA. We argue that the black disk limit corresponds to $R_{A/p}=1$ and $R^{\rm coh}_{A/p}=0.86$ for the summed and coherent scattering, respectively. Relying on an intuitive definition of the saturation scale, we show that the ratio of the saturation scales of a heavy nucleus and proton $Q_{sA}^2(b)/Q_{sp}^2(b) \approx 1$ at small impact parameters $b$ due to the strong leading twist nuclear shadowing and diluteness of the nuclear density.

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