Grant: Subatomic Physics Envelope - Individual

The most exotic state of nuclear matter obtained under extreme conditions is the Quark-Gluon Plasma (QGP), where quarks and gluons - the fundamental building blocks of nuclear interactions - are deconfined. While there has been significant effort in constraining off-equilibrium viscous properties of the QGP using low-energy particle spectra, the role of viscosity on penetrating high-energy probes, such the collimated spray of particles known as a jet, has not been investigated. To close this gap in knowledge, the proposed research program investigates how viscosity affects the quenching of jets in the QGP. Studying the effects of viscosity is used as a platform to systematically account for previously neglected physical mechanisms as a source of theoretical systematic uncertainty. These uncertainties methodically evaluate the level of confidence for Bayesian constraints on established quantities such as viscosity. My proposed program will study the effects of viscosity on jets, based on how their scattering kernel in the QGP is modified by viscous dissipation, and further investigates how high-energy electromagnetic probes emitted during jet showers are modified by dissipation. The latter will be used as an independent observable to confirm understanding gained from jets. A two-step approach is employed herein. The first step accounts for theoretical systematic uncertainties by studying how particle distributions are modified as function of viscous dissipation. Two different expansion bases of the particle distribution function in the Boltzmann equation will be used to account for the effects of viscosity: namely, the Chapman-Enskog gradient expansion and the Grad irreducible moment expansion. The second step of the proposed program is to study how viscous dissipation (be it via Chapman-Enskog and Grad moment expansions) affects the quenching of jet showers in the QGP. In particular, the viscous modifications of jet quenching transport coefficients, such as the mean transverse momentum acquired by jets traversing the QGP, will be explored. To that end, Bayesian model-to-data comparison will be used to constrain both the inviscid and viscous contributions to jet quenching. The viscous correction can be seen as a theoretical systematic uncertainty of previous Bayesian constraints of inviscid jet quenching transport coefficients, while the Chapman-Enskog versus Grad moment expansions quantify our understanding of the viscous effects themselves. The systematic approach developed herein illustrates a way to account for theoretical systematic uncertainties on Bayesian constraints. This program paves the way for how more robust Bayesian analysis of nuclear medium are to be obtained, highlights where better measurements are needed, thus increasing the interaction between theory and experiment. This discovery program will also train highly qualified personnel in fundamental physics and efficient numerical simulations of interest to academia and industry.