Speaker
Description
Hyperon-proton scattering experiment is one of the most direct methods to study the hyperon-nucleon interaction, as in the case of the $NN$ interaction. Although it had been experimentally difficult for a long time due to short lifetime of hyperons, we successfully performed novel high-statistics $\Sigma^\pm p$ scattering experiment at J-PARC (J-PARC E40 experiment). The main physics motivation was verification of a strong repulsive force due to Pauli effect in the quark level (quark Pauli effect) in $\Sigma N (I=3/2)$ system by measuring the differential cross sections of the $\Sigma^+ p$ elastic scattering. Measurements of the differential cross sections of the $\Sigma^- p$ elastic and $\Sigma^- p \to \Lambda n$ inelastic scattering also provide systematic information on $\Sigma N$ interaction.
The experiment was performed at the K1.8 beam line in the J-PARC Hadron Experimental Facility by June 2020.
Both of the incident $\Sigma^\pm$ production via the $\pi^\pm p \to K^+ \Sigma^\pm$ reaction and the $\Sigma^\pm p$ scattering occurred in a liquid hydrogen ($\text{LH}_2$) target. The $\Sigma^\pm$ production reaction was analyzed using the two spectrometers and the momentum of the $\Sigma^\pm$ was tagged event by event. The recoil proton from the $\Sigma^\pm p$ scattering was measured using CATCH, detector system surrounding the $\text{LH}_2$ target. The $\Sigma^\pm p$ scattering was identified by checking the kinematical consistency for the recoil proton. We identified thousands of scattering events for each channel and obtained the differential cross sections with good precisions. Their uncertainties were typically 10-20 $\%$ with an angular step of $\Delta\cos\theta_{\text{CM}}=0.1$ and the data quality was drastically improved in comparison with past experiments. These data is reliable input for theoretical models describing the baryon-baryon interactions ($BB$ interatcions), such as $\chi$EFT.
Moreover, owing to the precise data points and the simple representation of the $\Sigma^+ p$ system with respect to the multiplets of the $BB$ interaction, we could perform phase-shift analysis and obtain the $^3S_1$ and $^1 P_1$ phase shifts of the $\Sigma^+ p$ elastic scattering. Especially, S-wave phase shift can be compared with lattice QCD calculations such as HALQCD, where a calculation of higher partial-wave contribution is still difficult.
In this talk, I will introduce the J-PARC E40 experiment and results, mainly focusing on the $\Sigma^+ p$ elastic scattering. There are plans of further hyperon-nucleon scattering ($\Lambda p$ and $\Sigma^\pm p$) experiments at J-PARC.I would like to mention them.
