Speaker
Description
Hyperon-proton scattering experiment is one of the most direct methods to study the $YN$ interaction, as in the case of the $NN$ interaction. Although it was experimentally difficult due to short lifetime of hyperons for a long time, we successfully performed novel high-statistics $\Sigma p$ scattering experiment at J-PARC (J-PARC E40 experiment). One of the physics motivations 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.
The experiment was performed at the K1.8 beam line in the J-PARC Hadron Experimental Facility by June 2020 for the data collection of the $\Sigma^+ p$ scattering.
Both of production of $\Sigma^+$ beam via the $\pi^+p \to K^+ \Sigma^+$ reaction and the $\Sigma^+ p$ scattering occurred in a liquid hydrogen ($\text{LH}_2$) target. The $\Sigma^+$ production reaction was analyzed using the two spectrometers and the momentum of the $\Sigma^+$ beam was tagged event by event. The recoil proton from the $\Sigma^+ p$ scattering was measured using CATCH, detector system surrounding the $\text{LH}_2$ target.
The $\Sigma^+ p$ scattering was identified by checking the consistency for the recoil proton between the measured energy and the calculated energy from kinematics. In total, approximately 2400 $\Sigma^+ p$ elastic scattering events were identified in the $\Sigma^+$ momentum range of 0.44 to 0.80 GeV/$c$.
The differential cross sections of the $\Sigma^+ p$ scattering were derived for the three separated-momentum regions. Their uncertainties were typically less than 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. The obtained values of differential cross sections are around 2 mb/sr, which are not so large as most theoretical predictions.
Moreover, owing to precise data points and the simple representation of the $\Sigma^+ p$ system with respect to the multiplets of the $BB$ interaction, we could experimentally derive the phase shifts of the $^3S_1$ and $^1 P_1$ channels for the first time by performing the phase-shift analysis for the obtained differential cross sections. Especially, the phase shift of the $^3S_1$ channel, wherein a large repulsive core due to the quark Pauli effect was predicted, was evaluated to be $20^\circ<|\delta_{^3S_1}|<35^\circ$ for the present momentum range. This result suggests that the strength of repulsive force in $\Sigma N (I=3/2)$ system is moderate.
In this presentation, I will introduce J-PARC E40 experiment and analysis procedures to derive the differential cross sections and phase shifts of the $^3S_1$ and $^1P_1$ states for the $\Sigma^+ p$ elastic scattering.
By comparing our results to theoretical calculations, the nature of the $\Sigma^+ p$ interaction will also be discussed.
