What carries the baryon number in a proton, the strictly conserved quantum number in the Universe?
演講者 : Prof. Zhangbu Xu 許長補 特聘教授 (Brookhaven National Laboratory)
演講地點 : 理學教學新大樓物理系1F 36102教室
演講時間 : 2023 / 10 / 06 14:10
Baryon number (B) is a conserved quantum number that prevents protons (B = 1) and stable nuclei from disintegration and governs the visible Universe as it is today. It is conventionally assumed that the unit baryon number in a nucleon is distributed equally among its three valence quarks. An alternative picture was proposed at the birth of the theory of the Quantum Chromodynamics (QCD) half a century ago that the baryon number is instead traced by the baryon junction, a non-perturbative Y-shaped topology of gluons that is connected to all three valence quarks in most of the physics processes. Neither of these pictures have been experimentally verified while different experiments have demonstrated the fractional charges carried by the quarks. Relativistic heavy-ion collisions provide the necessary tools to study baryon transports in a non-perturbative way over large rapidity distance. I will present three experimental results we carried out at the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory in the US recently to test the hypotheses using isobar and Beam Energy Scan data collected by the STAR Collaboration. I will also review the previous experimental measurements in lepton+hadron and p+p collisions relevant to this topic, and discuss what we can do in the future at RHIC, the LHC and EIC.