Speaker
Description
In quantum chromodynamics (QCD), the baryon number is a conserved quantity. It is traditionally assumed to be evenly distributed among valence quarks in nucleus. However, an alternative framework proposes that this number is carried by a non-perturbative, Y-shaped topology of gluons connecting to three quarks. While neither hypothesis has been conclusively verified experimentally, new observations from the STAR Collaboration provide insights challenging the conventional valence quark picture.
In this talk, we will present STAR’s measurements from Ru+Ru and Zr+Zr collisions of the ratio of net baryon number (B) to the net charge difference (ΔQ = Q(Ru) − Q(Zr)) within mid-rapidity (|y| < 0.5), as well as net-proton yields from photonuclear Au+Au collisions as a function of rapidity. We find that the measured B/ΔQ far exceeds the expectation based on valence quarks. In addition, net-proton yields from photonuclear Au+Au collisions show weaker rapidity dependence than models without junction interactions. These results all favor the baryon junction hypothesis: since the junction composes of low-momentum gluons, it is easily stopped and results in enhanced baryon number being transported to mid-rapidity.
email: ctsang@bnl.gov