2023/12/13 by E. Mornacchi, Mornacchi, E., P. Pedroni +121
Physics and Astronomy · #FOS: Physical sciences #Nuclear Experiment (nucl-ex) #Nuclear physics research studies #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2312.08211
openalex publication_date 2023/12/13 · openalex created_date 2023/12/15 · openalex updated_date 2026/08/01
A new data set for the helicity-dependent differential cross section of the single-meson photoproduction reaction γp → p π0 was obtained for the photon energy interval 150-400 MeV. The experiment was performed at the A2 tagged photon facility of the Mainz Microtron MAMI using a circularly polarized photon beam and a longitudinally polarized proton target. The reaction products were detected with the large acceptance Crystal Ball/TAPS calorimeter covering 97% of the full solid angle. These new results, obtained with a fine energy and polar angle binning, greatly increase both the existing quantity and quality of the data available for this observable. A moment analysis, based on a finite expansion in Legendre polynomials, was applied to these data by using a bootstrap-based fitting method to correctly account for their systematic uncertainties. From the resulting decomposition of the differential cross sections, the E2/M1 ratio for the N→ Δ(1232) transition was determined to be [-2.38 ± 0.16\hbox (stat.+sys.) ± 0.10 \hbox (model)] %. Combining this value with previous results also allowed us to evaluate the most precise available estimate of the E2/M1 ratio to be used for all further reference and model comparisons.