从p+p到Pb+Pb碰撞中奇异夸克产生的系统尺寸依赖性：$K^+/π^+$ 峰的定量检验
System-size dependence of strangeness production from p+p to Pb+Pb: quantitative tests of the $K^+/π^+$ horn
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中文总结 AI 辅助
本研究通过多种理论模型与多系统碰撞数据对比，定量检验$K^+/π^+$峰的系统尺寸依赖性，发现奇异夸克增强存在阶梯式特征，为核形成与热力学平衡的区分提供了实验证据。
中文摘要 AI 辅助
中心Pb+Pb碰撞中观测到的$K^+/π^+$激发函数的显著极大值（“峰”）是碰撞能量依赖性的已确立特征，但它对系统尺寸的依赖性仍知之甚少。我们将强子输运模型SMASH、部分子输运模型PHSD、Glauber核-冕模型、正则系综抑制模型以及早期两阶段统计模型SMES，与覆盖NA61/SHINE完整系统尺寸序列（p+p、Be+Be、Ar+Sc、Xe+La）以及NA49的Pb+Pb和STAR的Au+Au数据的$K^+/π^+$结果进行对比，通过$\u03c7^2$量化每一项比较。没有单一框架能描述全部范围：核-冕模型更适合中间系统，带正则奇异夸克守恒的SMES适合重系统，且没有模型能重现小系统数据。无论是否包含部分子自由度，两种输运模型都无法产生该峰。数据显示$K^+/π^+$在Be+Be和Ar+Sc之间存在阶梯式增强，在核-冕框架下可量化为$f_{core}$从约0.22（Be+Be）跃升至约0.58（Ar+Sc）。奇异夸克饱和因子$\u03b3_S$以两个不同台阶上升，将几何核形成与热力学平衡区分开。在固定$\u221as_{NN}$下可抵消与系统无关的$\u03bc_B$贡献的$(K^+/π^+)/(K^-/π^-)$双重比，显示轻系统与重系统之间存在台阶，全局显著性为$3.7\u03c3$，为超出对产生基线的真实奇异夸克增强提供了证据。初步的Xe+La数据更支持核-冕模型（$\u03c7^2/ndf = 5.8$）而非SMASH（$\u03c7^2/ndf = 23.3$）；最终的能谱将在27%的水平上提升核-冕模型与SMES的区分度。
英文摘要
The pronounced maximum ("horn") in the $K^+/π^+$ excitation function observed in central Pb+Pb collisions is well established feature of collision-energy dependence, but its dependence on system size remains poorly understood. We confront hadronic (SMASH) and partonic (PHSD) transport, Glauber core-corona, canonical-ensemble suppression, and the two-phase statistical model of the early stage (SMES) with $K^+/π^+$ data spanning the complete NA61/SHINE system-size ladder (p+p, Be+Be, Ar+Sc, Xe+La) together with NA49 Pb+Pb and STAR Au+Au, quantifying every comparison by $χ^2$. No single framework describes the full range: core-corona is preferred for intermediate systems, SMES with canonical strangeness conservation for heavy systems, and none reproduces the small-system data. Neither transport model generates the horn, with or without partonic degrees of freedom. The data exhibit a step-like enhancement of $K^+/π^+$ between Be+Be and Ar+Sc, quantified within the core-corona framework by a step from $\fcore \approx 0.22$ (Be+Be) to $\fcore \approx 0.58$ (Ar+Sc). The strangeness saturation factor $\gs$ rises in two distinct steps, separating geometric core formation from thermodynamic equilibration. The $(K^+/π^+)/(K^-/π^-)$ double ratio, which at fixed $\sqrts$ cancels the system-independent $μ_B$ contribution, shows a step between light and heavy systems at a global significance of $3.7σ$, providing evidence for genuine strangeness enhancement beyond the pair-production baseline. Preliminary Xe+La data favor core-corona ($\chindf = 5.8$) over SMASH ($\chindf = 23.3$); finalized spectra will sharpen the CC/SMES discrimination at the $27\%$ level.
