2020/03/05 by Satoshi Nakamura, T. Ishikawa, Nakamura, Satoshi X. +3
Earth and Planetary Sciences · Physics and Astronomy · #FOS: Physical sciences #Geophysics and Gravity Measurements #High Energy Physics - Phenomenology (hep-ph) #Nuclear Experiment (nucl-ex) #Nuclear Theory (nucl-th) #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2003.02497
openalex publication_date 2020/03/05 · openalex created_date 2024/04/10 · openalex updated_date 2026/07/28
We discuss the possibility of extracting the neutron-neutron scattering length ann and effective range rnn from cross section data (d2σ/dMnn/dΩπ), as a function of the nn invariant mass Mnn, for π+ photoproduction on the deuteron (γd→ π+nn). The analysis is based on a γd→ π+nn reaction model in which realistic elementary amplitudes for γp→ π+n, NN→ NN, and πN→ πN are built in. We show that Mnn dependence (lineshape) of a ratio R\rm th, d2σ/dMnn/dΩπ normalized by dσ/dΩπ for γp→π+ n and the nucleon momentum distribution inside the deuteron, at the kinematics with θπ=0^∘ and Eγ∼ 250 MeV is particularly useful for extracting ann and rnn from the corresponding data R\rm exp. It is found that R\rm exp with 2% error, resolved into the Mnn bin width of 0.04 MeV (corresponding to the pπ bin width of 0.05 MeV/c), can determine ann and rnn with uncertainties of ± 0.21 fm and ± 0.06 fm, respectively, for the case of ann=-18.9 fm and rnn=2.75 fm. The requirement of such narrow bin widths indicates that the momenta of the incident photon and the emitted π+ have to be measured with high resolutions. This can be achieved by utilizing virtual photons of very small Q2 from electron scattering at Mainz MAMI facility. The proposed method for determining ann and rnn from γd→ π+ nn has a great experimental advantage over the previous one utilizing π- d→γnn for being free from the formidable task of controlling the neutron detection efficiency and its uncertainty.