Soudi, Ismail., Zhao, Wenbin., Majumder, Abhijit., Shen, Chun., Putschke, Jörn Henning., Boudreaux, B., Angerami, Aaron., Arora, R., Bass, Steffen A., Chen, Yuchen., Datta, R., Du, Lipei., Ehlers, Raymond J., Elfner, Hannah., Fries, Rainer J., Gale, Charles., He, Yayun., Jacak, Barbara V., Jacobs, Peter M., Jeon, Sangyoung., Ji, Yi Irene., Kasper, L., Kelsey, Matthew H., Kordell, Michael C., Kumar, Amit., Kunnawalkam-Elayavalli, Raghav., Latessa, J., Lee, Yen Jie., Lemmon, Roy Crawford., Luzum, Matthew., Mak, Simon., Mankolli, Andi., Martin, Christopher B., Mehryar, Haydar., Mengel, Tanner., Nattrass, Christine E., Norman, Jaime., Parker, Cody E., Paquet, Jean François François., Roch, Hendrik., Roland, Gunther., Schenke, Björn., Schwiebert, Loren., Sengupta, A., Singh, Mayank., Sirimanna, Chathuranga., Soeder, Derek., Soltz, R. A., Tachibana, Yasuki., Velkovska, Julia., Vujanovic, Gojko., Wang, X. N., & Wu, Xiangyu. (2025). Soft-hard framework with exact four-momentum conservation for small systems. Physical Review C, 112(1), 14905. https://doi.org/10.1103/r8jt-1xpk
We present x-scape, a new framework to study high-energy collisions between protons (𝑝−𝑝) and between protons and atomic nuclei (𝑝−𝐴). These collisions produce particles that move in different ways: some carry high momentum (hard processes), while others move more gently (soft processes). Our model starts by placing small “hotspots” of energy inside each proton or nucleon. When two hotspots collide, they create high-momentum particles, simulated with the Pythia generator. The early radiation emitted by these particles is modeled with a new tool called I-matter, which also accounts for where along the beam these emissions occur.
The energy used to produce these high-momentum particles is subtracted from the surrounding hotspots, which affects the creation of the bulk of the medium in the collision. The resulting showers of particles are simulated with the matter generator, and we explore cases both with and without energy loss. We then compare our predictions to experimental data on single particles and jets from 𝑝−𝑝 and 𝑝−Pb collisions. Using data from single particles, we fine-tune the model parameters with a Bayesian calibration. The comparisons show that x-scape can reproduce key features of the data, highlighting its usefulness. Finally, we study how the momentum of jets (𝑝𝑇) relates to the overall activity in the collision, helping us understand the complex dynamics of high-energy particle interactions.
FIG. 1.
Workflow of the x-scape-gim event generator for small collision systems.