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Thermal effects in QCD and Dilepton production.

Grant number: 23/17722-0
Support Opportunities:Scholarships abroad - Research Internship - Doctorate (Direct)
Effective date (Start): March 01, 2024
Effective date (End): February 28, 2025
Field of knowledge:Physical Sciences and Mathematics - Physics - Elementary Particle Physics and Fields
Principal Investigator:Josif Frenkel
Grantee:Gustavo Sadao Soares Sakoda
Supervisor: Mikko Laine
Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Research place: University of Bern, Switzerland  
Associated to the scholarship:22/15419-6 - Infrared Effects in QCD at finite temperature, BP.DD

Abstract

Quantum Chromodynamics (QCD) today is the well-established theory of strong interactions, characterized by a renormalizable non-Abelian gauge field theory with the color group SU(3). The coupling constant in QCD varies with energy scale, exhibiting asymptotic freedom at high energy scales. However, at lower energy scales, the coupling constant increases, leading to the breakdown of perturbation theory and the observation of the confinement phase transition.At zero temperature, for densities of the order of the nuclear density, quarks and gluons are confined in hadrons, a composite subatomic particles made of two or more quarks maintained together by the strong interaction in color-neutral bound states. The Drell-Yan process, involving lepton pair creation in hadron collisions, serves as a crucial event in high-energy colliders.Numerical simulations of lattice QCD at finite temperature has been decisive in convincing physicists that a phase transition should occur for sufficiently high temperatures and/or densities, called the de-confinement phase. When the temperature rises above a "critical temperature", then one obtains the quark-gluon plasma, where quarks and gluons are bound only weakly, free to move on their own. This project focuses on analyzing radiative thermal production rates of lepton pairs (dileptons) and thermal photons within the quark-gluon plasma, experimentally measurable in heavy-ion collisions.In the investigation of these phenomena, perturbative calculations are employed to explore kinematic domains, emphasizing massive or massless quarks at NLO with vanishing momentum. The Hard Thermal Loop (HTL) resummation is utilized to push energy toward a 'soft' regime. However, as we approach the light cone, perturbation theory breaks down, requiring LPM resummation (Landau-Pomeranchuk-Migdal) for treatment. The proposed visit aims to understand LPM resummation in this context, contributing to the improvement and development of our understanding of thermal field theories.This initiative extends the associated PhD project, connecting experimental data from heavy-ion collisions, Lattice QCD, and perturbative approaches.

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