Dr. Nicole Lewis, Rice University
Abstract:
The proton is far more complex than a simple bound state of three quarks. The experimental observation of strikingly large transverse single-spin asymmetries (TSSAs) revealed significant spin-momentum correlations present in hadronic collisions, requiring a more three-dimensional picture of the proton鈥檚 internal structure. This talk will discuss three different TSSA measurements conducted at the PHENIX experiment in proton-proton collisions that are sensitive to gluon dynamics within the proton. I will also discuss new experimental results sensitive to the carrier of the baryon number, a strictly conserved quantum number, which allows for the formation of stable atomic nuclei. In conventional models, baryon number is carried by the three valence quarks within a baryon. An alternative model called the baryon junction attributes the baryon number to a Y-shaped configuration of low-momentum gluons connected to all three valence quarks. This talk will discuss a measurement of photonuclear collisions, a type of nucleus-nucleus collision in which one nucleus emits a photon that scatters off the other colliding nucleus. In inclusive photonuclear collisions in Au + Au collision data at the STAR experiment, a significant excess of baryons compared to antibaryons was measured which is not consistent with the conventional baryon number carrier model. Together, these measurements provide new insight into the role of gluons in proton structure and baryon number transport and motivate future studies at CLAS12 in Hall B at Jefferson Laboratory and the upcoming electron-ion collider.