Measure charge transport in high-energy nuclear collisions with an energy scan of isobaric collisions

TL;DR

This paper proposes a novel method using isobaric collision energy scans to measure electric-charge transport in high-energy nuclear collisions, aiming to better understand charge redistribution mechanisms in QCD matter.

Contribution

It introduces a double-ratio technique to extract charge transport and demonstrates its sensitivity through simulations with different models and baryon transport scenarios.

Findings

Charge transport decreases exponentially with rapidity gap.

Model dependence observed in the slope parameter of charge transport.

Different patterns in baryon vs. electric-charge transport reveal underlying mechanisms.

Abstract

We present a method to measure electric-charge transport in high-energy nuclear collisions using a beam-energy scan of isobaric systems. Comparing collisions of nuclei with identical mass number but different atomic number allows the charge difference ($\Delta Q$) to be extracted with a double-ratio technique that suppresses most experimental systematic uncertainties. By varying the beam energy, the rapidity gap ($\Delta y$) over which electric charge is transported can be systematically scanned. Simulations of Ru+Ru and Zr+Zr collisions at $\sqrt{s_{\rm NN}}$=19.6-200GeV with UrQMD and PYTHIA Angantyr show that midrapidity $\Delta Q$ decreases exponentially with increasing $\Delta y$, with the slope parameter exhibiting strong model dependence. Comparisons with the baryon number transport reveal distinct patterns. In both UrQMD and PYTHIA Angantyr (with and without final-state baryon junctions), where baryon number is carried solely by valence quarks, the rapidity slope for baryon transport is larger than that for electric-charge transport. In contrast, scenarios that include baryon junctions in the initial state are expected to produce the opposite trend. This demonstrates that an isobar beam-energy scan provides a sensitive probe of electric-charge transport and offers new constraints on the microscopic mechanisms governing conserved-charge redistribution in QCD matter.