"Figure 12 (middle, left)" of "Measurement of the central exclusive production of charged particle pairs in proton-proton collisions at $\sqrt{s} = 200$ GeV with the STAR detector at RHIC"

Differential fiducial cross section for CEP of $K^+K^-$ pairs as a function of the invariant mass of the pair, for events with $\Delta\varphi < 90$ degrees.

Systematic uncertainties assigned to data points are strongly correlated between bins and should be treated as allowed collective variation of all data points. There are two components of the total systematic uncertainty. The systematic uncertainty related to the experimental tools and analysis method is labeled "syst. (experimental)". The systematic uncertainty related to the integrated luminosity (fully correlated between all data points) is labeled "syst. (luminosity)".

Fiducial region definition:
* central state $K^+$, $K^-$
- $p_{\mathrm{T}} > 0.3~\mathrm{GeV}$
- $min(p_{\mathrm{T}}(K^+), p_{\mathrm{T}}(K^-)) < 0.7~\mathrm{GeV}$
- $|\eta| < 0.7$
* intact forward-scattered beam protons $p'$
- $p_x > -0.2~\mathrm{GeV}$
- $0.2~\mathrm{GeV} < |p_{y}| < 0.4~\mathrm{GeV}$
- $(p_x+0.3~\mathrm{GeV})^2 + p_y^2 < 0.25~\mathrm{GeV}^2$
* additional cuts
- $\Delta\varphi < 90$ degrees

针对$K^+K^-$对的中心独家产生过程（Central Exclusive Production，CEP）的微分 fiducial截面（fiducial cross section），以该粒子对的不变质量为函数变量，对应$Deltavarphi < 90^circ$的事例。
各数据点对应的系统不确定度在各分箱间存在强相关性，应将其视为所有数据点的统一集体涨落进行处理。总系统不确定度包含两个分量：与实验装置及分析方法相关的系统不确定度标注为"syst. (experimental)"；与积分亮度相关的系统不确定度（所有数据点间完全相关）标注为"syst. (luminosity)"。
fiducial区域定义（fiducial region definition）：
· 中心态$K^+$、$K^-$：
- 横向动量$p_mathrm{T} > 0.3 mathrm{GeV}$
- $K^+$与$K^-$的横向动量最小值$min(p_mathrm{T}(K^+), p_mathrm{T}(K^-)) < 0.7 mathrm{GeV}$
- 赝快度$|eta| < 0.7$
· 完整的前向散射束流质子$p'$：
- 横向动量分量$p_x > -0.2 mathrm{GeV}$
- $0.2 mathrm{GeV} < |p_y| < 0.4 mathrm{GeV}$
- $(p_x + 0.3 mathrm{GeV})^2 + p_y^2 < 0.25 mathrm{GeV}^2$
· 额外筛选条件：
- $Deltavarphi < 90^circ$