A B-factory continuum retune of PYTHIA 8 hadronization parameters using BELLE and BABAR identified-hadron data

Abstract

We refine the hadronization sector of a pp PYTHIA~8 tune in $e^+e^-\to q\bar q$ production using selected BELLE and BABAR measurements near the $\Upsilon(4S)$ region. The study is performed with PYTHIA~8.316 and Rivet~4.1.1 and is restricted to parameters used in this $e^+e^-$ setup. Starting from the five-parameter hadronization subset of the pp tune, we carry out a staged extension guided by the remaining differences in the BELLE and BABAR data. The final comparison uses a fixed common set of 20,803 bins and samples of 1,000,000 generated events per analysis and tune point. On this basis, the selected refined tune gives a bin-weighted score of 73.42, compared with 76.49 for the Skands $e^+e^-$ reference and 79.22 for Monash~2013 $e^+e^-$. It remains the best-scoring tune for the BELLE charged-hadron, baryon, and single- and dihadron measurements, while Skands still performs better for the BABAR charged-hadron sample and the BELLE meson sample. The bin-weighted ordering is driven primarily by the BELLE 2020 sample. The refined tune gives a small but stable improvement for the selected BELLE and BABAR measurements, although clear differences between the individual datasets remain.