Speaker
Description
We have been carrying out photoproduction experiments by using linearly polarized tagged photon beams with energies of 1.5-2.9 GeV at SPring-8/LEPS. Charged pions and kaons were detected at forward angles. We studied the $\gamma p$ -> $\pi^{-}\Delta^{++}$, $\pi^{+}n$, and $K^{+}\Lambda$($\Sigma^{0}$) reactions. In the final states of these reactions, $u\bar{u}$, $d\bar{d}$, and $s\bar{s}$ quark-antiqurk pairs are produced, respectively. The differential cross sections and photon beam asymmetries were measured. It is interesting that only the $\pi^{-}\Delta^{++}$ reaction is found to have negative asymmetries and the other reactions have positive asymmetries. In the $\pi^{-}\Delta^{++}$ reaction, a d quark in the proton is replaced with a u quark. In the other reactions, a u quark is replaced with a d or an s quark. The difference in asymmetries might originate from different characteristics between the u and d quarks in the proton. We newly analyzed the data for the $\gamma p$ -> $\pi^{+}\Delta^{0}$ reaction. The comparison between the $\pi^{-}\Delta^{++}$ and $\pi^{+}\Delta^{0}$ reactions plays an important role for distinguishing $N^{*}$ from $\Delta^{*}$ in the s channel. We present preliminary results for the $\pi^{+}\Delta^{0}$ reaction in the NSTAR2019 workshop.
