Hybrid Hadronization with Color Flow
Abstract
Hybrid Hadronization is an approach that combines two well-established models, string frag- mentation and recombination, to describe the hadronization of QCD jets. It is available as a code written and maintained by Professor Fries’ group at Texas A&M university and it is a part of the JETSCAPE framework [1]. My project improves the physics of the current Hybrid Hadronization code to be closer to realistic Quantum Chromo Dynamics (QCD) by working on two related issues. The first one is about utilizing known information about the color states of quark-antiquark pairs or quark triplets in determining the probability of recombination. Previously, the probability for quark-antiquark pairs to form color singlet state was set to 1/9 as default, and that for three quarks to form color singlet was set to 1/27 These are the values appropriate if color quantum numbers are completely randomized. The improved code now modifies these values based on the color states of partons chosen.
The second issue concerns the string repair process. Based on the result of the recombination step, the code organizes remnant strings and temporary junctions by tracing color flow, which is given by the color tags that were generated by jet shower modules, and utilizes these information for repairing strings after recombination. Subsequently it processes temporary junctions to be compatible with PYTHIA by cutting problematic junctions, checking conservation laws, and assigning the history tags to define final partons in junctions. My improved Hybrid Hadronization code can, for the first time, run with MATTER and LBT parton shower input and add thermal partons in a way that utilizes both the space-time information and the color information provided by these codes correctly. We have studied the systematic behavior of jet hadronization for different jet energies and medium sizes. We find typical recombination signatures, like baryon / meson ratios and flow effect as expected with medium size. This opens the door for further explorations of hadronization and jet physics using JETSCAPE and the Hybrid Hadronization code.
Citation
Kim, Byunggyu (2020). Hybrid Hadronization with Color Flow. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /192558.