Early-Times Yang-Mills Dynamics and the Characterization of Strongly Interacting Matter with Statistical Learning

Area of Science:

• Nuclear Physics
• High-Energy Physics
• Quantum Chromodynamics

Background:

• Ultrarelativistic heavy-ion collisions create quark-gluon plasma (QGP).
• Early collision dynamics (before ~1 fm/c) are complex and modeled parametrically.
• Parametric models impact the predictive power of QGP calculations.

Purpose of the Study:

• To systematically analyze LHC Pb-Pb collision data.
• To obtain precise constraints on the shear and bulk viscosity of QGP.
• To account for theoretical uncertainties in the QGP evolution and hadronization.

Main Methods:

• Combined an ab initio model for early-stage collisions with a hydrodynamic model for QGP evolution.
• Utilized Bayesian model averaging and transfer learning to manage computational costs and uncertainties.
• Calibrated models against LHC measurements from Pb-Pb collisions.

Main Results:

• Achieved state-of-the-art constraints on QGP shear and bulk viscosity.
• Found that a constant specific shear viscosity is statistically preferred over a temperature-dependent one, despite apparent strong constraints.
• Validated the model using discriminating observables not included in the calibration, showing excellent agreement.

Conclusions:

• The study provides robust constraints on QGP transport properties.
• Model predictivity and agreement with data do not necessitate a temperature-dependent shear viscosity.
• The combined modeling approach offers a reliable framework for studying QGP dynamics.