Photoproduction of p0 Mesons in Ultra-Peripheral D-AU Collisions at RHIC
The rho meson is copiously produced in high-energy collisions. Sometimes these oppositely directed beams of charged nuclei (ions) interact head-on resulting in a central collision. But often these nuclei narrowly miss each other and interact through electromagnetic fields. This phenomenon, known as an ultra-peripheral collision, is of particular interest because hadronic interactions are suppressed and photoproduction can be observed on a significant scale. Photoproduction can result in the creation of vector mesons like the rho meson. This work analyzes the deuterium-gold ultra-peripheral collision data collected during the 2016 run at the Relativistic Heavy Ion Collider (RHIC) to find the raw yield of the neutral rho meson, from which the cross section of the rho meson could be determined. I will describe the STAR detector and the criteria used to select the candidate rho mesons. While the rho meson decays very quickly into charged pions, it can be identified from the ionization tracks left by its daughter particles. This cross section of the rho meson in an asymmetric collision between gold and deuterium, would provide another data-point to determine how the photoproduction cross section of the rho meson varies with atomic mass number, which can provide insight into nuclear shadowing effects. I will compare the kinematic distributions of the daughter pions as well as the parent rho meson candidates with theoretical expectations. I analyzed data collected using two different trigger conditions, neither of which was optimized for detection of the rho meson. In both datasets, the number of rho mesons observed is too small for a meaningful measurement of the rho meson photoproduction cross section.
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