AI 中文总结
研究通过超外围重离子碰撞及电子离子对撞机中光子诱导产生来探测\(X(3700)\)，计算相关振幅并修饰粒子对，经卷积得到截面数据，发现近阈值特征受\(\gamma\gamma\to D\bar{D}\)动力学控制，为研究提供新环境及可观测量。
AI 中文摘要
我们研究在超外围重离子碰撞以及电子离子对撞机（EIC）中光子诱导产生过程是否能为寻找通常表示为\(X(3700)\)的标量\(D\bar{D}\)分子候选物提供新环境。计算了\(\gamma\gamma\to D^+ D^-\)和\(\gamma\gamma\to D^0 \bar{D^0}\)的树图振幅，在\((D^+ D^-, D^0 \bar{D^0})\)基下用耦合通道贝塞耳 - 萨尔皮特相互作用修饰出射粒子对，并将所得子过程截面与等效光子谱进行卷积。在采用的双通道情形下，\(T\)矩阵的解析延拓给出一个\(M_X = 3.7162\) GeV的束缚态，低于\(D^0 \bar{D^0}\)阈值。这导致连续态中观测到的信号不是简单的孤立窄峰，而是产生了特征性的近阈值线形畸变。给出了不同碰撞情形下\((D^+D^-,D^0 \bar{D^0})\)的积分修饰与裸截面比及修饰截面等数据。带电与中性比是可直接观测的量，而修饰与裸截面比提供了末态相互作用的理论诊断。近阈值特征由共同的\(\gamma\gamma\to D\bar{D}\)动力学控制，且相当独立于外部光子源。
英文摘要
We investigate whether photon-induced production in ultraperipheral heavy-ion collisions and at the EIC can provide a new environment to search for the scalar $D \bar{D}$ molecular candidate usually denoted as $X(3700)$. We calculate the tree-level amplitudes for $γγ\to D^+ D^-$ and $γγ\to D^0 \bar{D^0}$, dress the outgoing pair with a coupled-channel Bethe-Salpeter interaction in the $(D^+ D^- , D^0 \bar{D^0})$ basis, and convolute the resulting subprocess cross sections with equivalent-photon spectra. In the adopted two-channel scenario the analytic continuation of the $T$-matrix gives a bound state at $M_X=3.7162$~GeV, which is below the $D^0 \bar{D^0}$ threshold. As a consequence of this, the observed signal in the continuum is not simply an isolated narrow peak, and a characteristic near-threshold line-shape distortion is produced: around $3.70 \leq W \leq 3.85$~GeV the integrated dressed-to-bare ratios are $(13.71,0.35)$ in Pb-Pb UPCs and $(13.74,0.35)$ in $e$-Au collisions for $(D^+D^-,D^0 \bar{D^0})$. Using the BABAR-fitted central normalization $K_{\rm dressed}=0.382$, the corresponding dressed cross sections are $(24.6,14.6)~μ{\rm b}$ in Pb-Pb UPCs and $(2.41,1.43)~\rm nb$ at the EIC. The charged-to-neutral ratios are directly accessible observables, whereas the dressed-to-bare ratios provide theoretical diagnostics of the final-state interaction. The near-threshold features are controlled by the common $γγ\to D\bar{D}$ dynamics and are rather independent of the external photon source.
Comments21 pages, 11 figures
