LHC能区粲夸克强子化及总散射截面的ALICE实验研究

粲重子介子比是研究粲夸克强子化机制的有效工具。Λc/D0在LHC能区比正负电子碰撞实验测量结果高，及在重离子碰撞中由于夸克胶子等离子体(QGP)的产生，Λc/D0较质子-质子碰撞进一步提高。这些结果表明粲夸克强子化机制在不同碰撞系统中存在差异。目前的理论模型还未能对这一现象提出合理解释。本项目将基于ALICE第二、三期取数，融合卡尔曼滤波算法与深度机器学习算法，优化短寿命粒子重建方案，实现对更高质量粲重子(Σc,Ξc,Ωc)的横动量谱的精确测量；通过粲重子/介子及重子/重子比检验强子化机制的各类模型；通过粲夸克总散射截面的测量检验微扰QCD理论预言；通过粲夸克碎裂函数的测量并与正负电子实验结果比较，检验理论上关于碎裂函数普适性的假设；通过比较强子与电子衰变道，得到粲重子的相对衰变分支比。以上均为LHC能区的首次测量，有助于完备理解粲夸克在不同碰撞系统中强子化机制的差异以及QGP引起的效应。

Studies on the production of heavy-flavor baryons are of prominent importance to investigate hadronization mechanisms at the LHC, in particular through the study of the evolution of the baryon-to-meson production ratio as a function of the transverse momentum. Measurements performed in pp and p-Pb collisions at the LHC have revealed unexpected features, qualitatively similar to what was observed in larger systems and, in the charm sector, not in line with the expectations based on previous measurements from e+e- colliders and in e-p collisions. This ratio has been found to be further enhanced in Pb-Pb collisions due to the formation of quark-gluon plasma (QGP). These results suggest that charmed baryon formation might not be universal and that the baryon-to-meson ratio depends on the collision system. Up to now, all of theoretical calculations underestimate the data measurements. There are two main purposes in this research project. In this project, we will develop a new strategy of particle reconstructions in ALICE based on the Kalman filter algorithm and machine learning technique, which can suppress the combinatorial background and improve the significance. Thus more charmed baryons with higher mass than Λc, such as Σc，Ξc，Ωc, can be measured in ALICE and the total charm cross section and charm fragmentation functions can be easily obtained. All these charmed baryons can be reconstructed by both hadronic and semi-leptonic decay channels to obtain relative decay branching ratios between different decay channels. It is the first time to measure the heavier charmed baryons transverse momentum spectrums at the LHC. They will provide essential tests on pQCD calculations, models of charm hadronization process and will set up a benchmark for Pb-Pb collisions to study the QGP effect on heavy flavor hadronization.