标题： 光产生和检测超周边碰撞及电子离子对撞机上的$ρ'\rightarrowπ^+π^-π^+π^-$衰变 显示英文标题

标题： Photoproduction and detection of $ρ'\rightarrowπ^+π^-π^+π^-$ decays in ultra-peripheral collisions and at an electron-ion collider

摘要： 矢量介子光生是探测原子核结构的重要方法。 轻矢量介子对低$-x$结构最为敏感，只要它们不是太轻而无法进行微扰QCD计算即可。 $\rho'$ 是一个中间质量态（介于 $\rho$ 和 $J/\psi$ 之间），比 $\phi$ 更容易探测，因此值得关注。 利用 HERA 质子靶数据，我们预测了大型强子对撞机和 RHIC 中 UPC 中铅/金靶的碰撞情况，以及未来电子-离子对撞机 (EIC) 中 $ep$ 和 $eA$ 碰撞的发生情况。 这些离子靶的投影取决于很大未知的$\rho'\rightarrow\pi^+\pi^-\pi^+\pi^-$分支比，并且使用现有数据来约束该分支比。 当前数据显示出相对较低的分支比，小于50%。 HERA 的$ep$和 ALICE 非中心碰撞的$e$铅数据表现出非常相似的$4\pi$质量谱，这表明，如果系统由两个共振组成，它们与四π分支比的光子耦合产物是相似的。 预测的速率对于非中心碰撞和电子离子对撞机（EIC）都较高。 $\rho'\rightarrow\pi^+\pi^-\pi^+\pi^-$衰变可以以高效率在EIC中被观测到。 在最高能量的$ep$碰撞中，需要前向 B0 探测器来观测这一通道，直到达到最低可实现的 Bjorken$-x$值。 显示英文摘要

摘要： Vector meson photoproduction is an important probe of nuclear structure. Light vector mesons are most sensitive to low$-x$ structure, as long as they are not too light for perturbative QCD calculations. The $\rho'$ is of interest as an intermediate mass state (between the $\rho$ and $J/\psi$) that is easier to detect than the $\phi$. Using HERA data on proton targets, we make projections for lead/gold targets in UPCs at the Large Hadron Collider and RHIC, and for $ep$ and $eA$ collisions at a future Electron-Ion Collider (EIC). These projections for ion targets depend on the largely-unknown $\rho'\rightarrow\pi^+\pi^-\pi^+\pi^-$ branching ratio, and use existing data to constrain that branching ratio. Current data points to a relatively low branching ratio, less than 50\%. The HERA $ep$ and ALICE UPC $e$Pb data exhibit very similar $4\pi$ mass spectra, indicating that, if the system is composed of two resonances, the products of their photon couplings with their four-pion branching ratios are similar. The predicted rates are high for both UPCs and the EIC. The $\rho'\rightarrow\pi^+\pi^-\pi^+\pi^-$ decay can be observed at the EIC with high efficiency. In $ep$ collisions at the highest energy, the forward B0 detector is needed to observe this channel down to the lowest achievable Bjorken$-x$ values.