Research highlight: High precision information of photo-production of Δ^(++) Resonances
The photo-production of Δ^(++) resonances from the proton target (γp→π^- Δ^(++)) is an interesting channel of studying the uu ̅ pair excitation. The production cross sections and beam asymmetries of this process also offers important information in gauging new nucleon resonances and understanding the low-energy hadronic interactions. Such data at the forward production direction and in low-energy regime becomes available recently from the LEPS experiment, using unique 1.5-2.95 GeV linearly-polarized Compton-backward scattered photon beam at SPring-8 facility, Japan. The results are published in Physics Review Letters (PRL 120, 202004 (2018)) on May 18, 2018.
Strong forward-peaking production from the t-channel π-exchange is confirmed in the high precision data of differential cross sections and beam asymmetries. The measured negative beam asymmetries are opposite to those from π^+ and K^+ photo-production, corresponding to the production of dd ̅ and ss ̅ pairs. It is intriguing that analogous results are observed in the measurements of the transverse single-spin asymmetries in the pp and ep reactions. Further investigations are needed to clarify any fundamental connection. These precise data will surely improve the theoretical modeling of the low-energy hadronic interactions as well as the identification of new nucleon resonances.
This work was initiated during Dr. Hideki Kohri’s visit of Institute of Physics, Academia Sinica in 2014. Later it was mainly accomplished by him and IPAS LEPS group members, Shiuan-Hal Shiu and Wen-Chen Chang.
Journal Links: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.202004