Speaker
Description
We performed the J-PARC E40 experiment to measure the $\Sigma p$ scattering from 2018 to 2020. Together with the $\pi^{-}p\to K^{+}\Sigma^{-}$ data, the $\pi^-p\to K^0\Lambda$ events were accumulated as by-product data. The analysis confirmed that $\Lambda$ could be identified with reasonable accuracy of S/N ratio $\sim2.67$. Plus, we found the polarization of $\Lambda$ ($P_{\Lambda}$) was preliminarily derived as 1.009 $\pm$ 0.049 for the $K^{0}$ angular range of $0.7 < cos\theta_{CM,K^{0}} < 0.8$, using the following equation:
\begin{equation}
\frac{1}{N_0}\frac{dN}{d\cos\theta_p} = \frac{1}{2}(1+\alpha P_{\Lambda}\cos\theta_p),
\end{equation}
where $N_0$ is the yield of the decay proton, $\alpha$ is the asymmetry parameter (= $0.750\pm0.009\pm0.004$). This result has higher accuracy than the past measurement [1].
The result above indicates that we can measure not only the $\Lambda p$ differential cross-section ($(d\sigma / d\Omega)_{\Lambda p}$) but also spin observables such as analyzing power ($A_{y}$) and depolarization ($D_{yy}$) with $\sim100\%$ polarized $\Lambda$ beam. These quantities are essential inputs for establishing the realistic $\Lambda N$ interaction.
Therefore, we plan a new $\Lambda p$ scattering experiment at J-PARC K1.1, Ibaraki, Japan [2] to measure $(d\sigma / d\Omega)_{\Lambda p}$, $A_{y}$ and $D_{yy}$ with better than 10$\%$ accuracy. I will mainly talk about the $P_{\Lambda}$ analysis in J-PARC E40 data and briefly introduce the next $\Lambda p$ scattering experiment.
[1] R. D. Baker et al., Nucl. Phys. B 141, 29 (1978).
[2] K. Miwa et al., J-PARC proposal P86., 2021.