Seminar in Hadronic Physics

Tracing the baryon number in relativistic isobar collisions at RHIC

Gregoire Pihan

Wayne State University

Traditionally, the baryon number and electric charge within a proton are attributed to the valence quarks. However, an alternative picture known as the “baryon junction” challenges this paradigm by proposing that the baryon charge is associated with a Y-shaped, non-perturbative gluonic configuration inside hadrons. Recent preliminary analyses of isobar collisions at the Relativistic Heavy Ion Collider (RHIC) reveal that the scaled net-baryon to net-electric charge number ratio at midrapidity (B/Δ Q * Δ Z/A) falls within the range of 1.5 to 2. This aligns with predictions derived from the baryon junction model, marking a significant development. This outcome strongly suggests that, in high-energy collisions, the carrier of the baryon number is the baryon junction rather than the valence quarks. However, it is important to note that existing predictions pertain solely to the initial collision stage. In this seminar I will talk about a comprehensive (3+1)D relativistic hydrodynamic framework incorporating multiple conserved charge currents to systematically investigate this measurement from the initial to the final stage. Simulating the coupled propagation of net baryon and electric charge currents and incorporating a charge-dependent lattice-QCD-based equation of state, we explore the evolution of these charges throughout various phases of heavy-ion collisions. At the initial stage I will concentrate on identifying the baseline for this ratio with a particular focus on the impact of the nuclear structure. At the final stage, I show the enhancement of the ratio, as measured in Ru+Ru and Zr+Zr collisions at √ s_NN=200 GeV, providing agreement with STAR preliminary measurements.