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arXiv 1512.08046hep-phhep-exhep-latnucl-exnucl-th
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在LHC从强子产额数据的热拟合中温度提取的令人惊讶的大不确定性

Surprisingly large uncertainties in temperature extraction from thermal fits to hadron yield data at LHC

Volodymyr Vovchenko, Horst Stoecker

备注：
8 pages, 3 figures, v3: added calculations for baryon-baryon only eigenvolume interactions fitted to nuclear ground state, added table with fitted data, title and discussion modified in order to ensure more clarity about the presented results
发表信息：
J. Phys. G 44, 055103 (2017)
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摘要：

采用传统的强子-共振气体（HRG）模型，结合粒子数据组（PDG）强子输入、完全化学平衡和强子型相关的本征体积相互作用，对ALICE合作组的最中心Pb+Pb碰撞强子中快度产额数据进行了拟合.对于点状强子的情况，我们得到了著名的拟合结果$T = 154 \pm 2$ MeV.然而，如果强子有不同的本征体积，情况就会改变。当所有的介子都是点状的，而所有的重子都有一个0.3微米的有效硬核半径的$χ^2$的$χ^2$温度依赖性的情况下，有一个广泛的最小值的温度范围内的$155-210$ MeV，与拟合质量相媲美的$T \sim 155$ MeV最小值的点粒子的情况下。当仅考虑重子-重子本征体积相互作用时，得到了非常相似的结果，本征体积参数取自之前对核物质基态的拟合。最后，当我们应用本征体积修正与质量成比例的本征体积$v_i \sim m_i$，固定到特定的质子硬核半径$r_p$，我们观察到第二个最小值的温度依赖性的$χ^2$，位于显着更高的温度。例如，在$r_p = 0.5$ fm处，在$170-320$ MeV的非常宽的温度范围内，拟合质量比点粒子HRG情况下更好，这给出了从拟合到150 MeV的数据的温度确定的不确定性。这些结果表明，热拟合的重离子强子产额数据是非常敏感的强子之间的短程排斥本征体积的建模，和化学冻结温度可以提取的LHC强子产额数据只有相当大的不确定性。

英文摘要：

The conventional hadron-resonance gas (HRG) model with the Particle Data Group (PDG) hadron input, full chemical equilibrium, and the hadron type dependent eigenvolume interactions is employed to fit the hadron mid-rapidity yield data of ALICE Collaboration for the most central Pb+Pb collisions. For the case of point-like hadrons the well-known fit result $T = 154 \pm 2$ MeV is reproduced. However, the situation changes if hadrons have different eigenvolumes. In the case when all mesons are point-like while all baryons have an effective hard-core radius of 0.3 fm the $χ^2$ temperature dependence of the $χ^2$ has a broad minimum in the temperature range of $155-210$ MeV, with fit quality comparable to the $T \sim 155$ MeV minimum in the point-particle case. Very similar result is obtained when only baryon-baryon eigenvolume interactions are considered, with eigenvolume parameter taken from previous fit to ground state of nuclear matter. Finally, when we apply the eigenvolume corrections with mass-proportional eigenvolume $v_i \sim m_i$, fixed to particular proton hard-core radius $r_p$, we observe a second minimum in the temperature dependence of the $χ^2$, located at the significantly higher temperatures. For instance, at $r_p = 0.5$ fm the fit quality is better than in the point-particle HRG case in a very wide temperature range of $170-320$ MeV, which gives an uncertainty in the temperature determination from the fit to the data of 150 MeV. These results show that thermal fits to the heavy-ion hadron yield data are very sensitive to the modeling of the short-range repulsion eigenvolume between hadrons, and that chemical freeze-out temperature can be extracted from the LHC hadron yield data only with sizable uncertainty.

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