2016/06/08 by Klein, Spencer R. · 1 citation
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High-Energy Particle Collisions Research #Nuclear Experiment (nucl-ex) #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.1606.02754
openalex publication_date 2016/06/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
In 2010, the STAR Collaboration collected 38 million low-multiplicity triggers for ultra-peripheral collision studies. We present new results involving photonuclear interactions in ultra-peripheral relativistic heavy ion collisions (UPCs), based on an analysis of 384,000 photoproduced pion pairs, from ρ, ω and direct π+π- pair production.The ω component is clearly visible through its interference with the ρ peak. The relative amplitudes of the three components have been measured, along with the phase angle between the ρ and ω components. Using a two-year (2010 and 2011) dataset, we explore higher mass final states, and observe a π+π- state with a mass of 1653 ± 10 MeV and a width of 164± 15 MeV (statistical errors only). The state is at least roughly compatible with the ρ3(1690). The ρ0 squared momentum transfer (t) spectrum exhibits a spectrum with both coherent and incoherent prodution. The coherent component shows two characteristic diffraction minima, with positions that are sensitive to the hadronic radius of the gold nucleus.