关于$X(3872)$质量及其计数率的精确测量
On the precise measurement of the $X(3872)$ mass and its counting rate
摘要：
已经发现，奇异态的特定产生实验的线形，如具有涉及三角形奇点的$J^{PC}=1^{++}$量子数的$X(3872)$，对弱束缚态的结合能变得高度敏感，从而在原则上提供基准测定的机会。我们批判性地分析了最近的建议，以准确和精确地提取的$X(3872)$质量，忽略了一个重要的物理效应，将其相应的生产线形状作为一个尖锐的质量分布，因此，忽略了初始附近的连续态的影响，在$1^{++}$通道。包含这些状态意味着一个有效的抵消机制，它在当前和有限的实验分辨率的检测器，使一个不能区分的$1^{++}$束缚态和附近的$D \bar D^*$连续态具有相同的量子数。特别是，我们表明，1兆电子伏以上的分辨率的线形变得相当不敏感的结合能，除非考虑高统计。观察到的隆起的存在仅仅是短距离相关的结合或未结合的$\bar D D^*$对的结果。取消也提供了一个自然的解释，最近的研究报告失踪，但未知的衰减通道的绝对分支比全球分析的$X(3872)$。
英文摘要：
The lineshapes of specific production experiments of the exotic state such as $X(3872)$ with $J^{PC}=1^{++}$ quantum numbers involving triangle singularities have been found to become highly sensitive to the binding energy of weakly bound states, thus offering in principle the opportunity of benchmark determinations. We critically analyze recent proposals to extract accurately and precisely the $X(3872)$ mass, which overlook an important physical effect by regarding their corresponding production lineshapes as a sharp mass distribution and, thus, neglecting the influence of initial nearby continuum states in the $1^{++}$ channel. The inclusion of these states implies an effective cancellation mechanism which operates at the current and finite experimental resolution of the detectors so that one cannot distinguish between the $1^{++}$ bound-state and nearby $D \bar D^*$ continuum states with the same quantum numbers. In particular, we show that the lineshape for resolutions above 1 MeV becomes rather insensitive to the binding energy unless high statistics is considered. The very existence of the observed bumps is a mere consequence of short distance correlated $\bar D D^*$ pairs, bound or unbound. The cancellation also provides a natural explanation for a recent study reporting missing but unknown decay channels in an absolute branching ratio global analysis of the $X(3872)$.
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