NPA Seminar: Nicole Lewis, Rice University, “Search for baryon number carrier in photonuclear processes and heavy-ion collisions at STAR”

Event time: 
Thursday, May 2, 2024 - 1:00pm to 2:00pm
Wright Lab, WL-216 (Conference Room) See map
272 Whitney Avenue
New Haven, CT 06511

Event description: 

Baryon number is a strictly conserved quantum number. It is conventionally assumed to be divided equally among the three valence quarks inside each baryon, but this has never been verified experimentally. An alternative model is the baryon junction: a Y-shaped configuration of nonperturbative gluons that is connected to all three valence quarks and carries the baryon number. In this talk we will present two measurements from the STAR experiment which are sensitive the baryon number carrier. One measurement compares baryon stopping to electric charge stopping over large momentum transfer using identified particle spectra in Ru+Ru and Zr+Zr isobar collisions. Given that valence quarks carry the baryon’s electric charge, if they also carried the baryon number, we would expect these quantities to be the same, but results show that at mid-rapidity baryon stopping is a factor of two larger than charge stopping in central collisions. Photonuclear collisions are a type of ultraperipheral heavy-ion collision where one nucleus emits a quasi-real photon which interacts with the other colliding nucleus. Significant baryon stopping and rapidity asymmetry are observed at low transverse momentum in semi-inclusive photonuclear processes in Au+Au collisions, further supporting the argument that baryon number is not carried by the valence quarks.

Host: Isaac Mooney