Tracking the baryon number with nuclear collisions

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Chromodynamics

Background:

• Baryon number conservation is a fundamental principle since the early Universe.
• The conventional model attributes baryon number to fractionally charged valence quarks.
• An alternative hypothesis suggests baryon number is carried by nonperturbative gluonic configurations called baryon junctions.

Purpose of the Study:

• To experimentally investigate the distribution of baryon number.
• To test the validity of the valence quark model versus the baryon junction hypothesis.
• To analyze baryon number over electric charge difference and net-proton yield.

Main Methods:

• Measurements of the baryon number (B) over electric charge number difference (ΔQ) at mid-rapidity in isobar nuclear collisions.
• Analysis of net-proton yield along rapidity in photonuclear collisions.
• Comparison of experimental data with theoretical models.

Main Results:

• A larger B/ΔQ ratio was observed than predicted by valence quark models.
• A less asymmetric net-proton yield was found compared to valence quark model predictions.
• Previous findings in Au+Au collisions corroborate these results.

Conclusions:

• The experimental results disfavor the conventional picture of baryon number being carried by valence quarks.
• The findings support further investigation into alternative models, such as the baryon junction hypothesis.
• This study provides crucial experimental constraints on the fundamental nature of baryon number.