Experimental plan of Σp scatterings at J-PARC

Department of physics, Tohoku university, High Energy Accelerator Research Organization (KEK)

^a e-mail: miwa9@lambda.phys.tohoku.ac.jp

Abstract

In order to test theoretical frameworks of the baryon-baryon interactions and to confirm the ”Pauli effect between quarks” for the first time, we propose an experiment to measure low-energy hyperon proton scattering cross sections in the following channels with high statistics, 1. Σ⁻ p elastic scattering, 2. Σ⁻ p → Λn inelastic scattering, 3. Σ⁺ p elastic scattering. According to theoretical models based on quark-gluon picture for the short range part of the baryon-baryon interactions, the Σ⁺ p channel is expected to have an extremely repulsive core due to the Pauli effect between quarks, which leads a Σ⁺ p cross section twice as large as that predicted by conventional meson exchange models with a phenomenologically treated short range repulsive core. In addition, measurement of the Σ⁻ p channel where the quark Pauli effect is not effective is also necessary to test the present theoretical models based on meson exchange picture with the flavor SU(3) symmetry. Thus this experiment will provide essential data to test the frameworks of the theoretical models of the baryon-baryon interactions and to investigate the nature of the repulsive core which has not been understood yet.

In order to overcome the experimental difficulties in measuring low-energy hyperon proton scattering, we will use a new experimental technique in which a liquid H₂ target is used as hyperon production and hyperon scattering targets with a detector system surrounding the LH₂ target for detection of a scattered proton and a decay product from a hyperon. The hyperon scattering event is kinematically identified. Because imaging detectors used in past experiments are not employed, high intensity π beam can be used, allowing us to take high statistics data of 100 times more than the previous experiments. We have proposed an experiment of Σp scattering at the K1.8 beam line by utilizing the K1.8 beam line spectrometer and the SKS spectrometer. A high intensity π beams of 2×10⁷/spill at 1.32 GeV/c and 1.42 GeV/c for the Σ⁻ and Σ⁺ productions, respectively, are used to produce as many hyperon beam as possible.With 16×10⁶ Σ⁻ beam and 55×10⁶ Σ⁺ beam around 500 MeV/c which are tagged by the spectrometers, we will detect ~10,000 Σ⁻ p and Σ⁺ p scattering events and ~6,000 Σ⁻ p → Λn inelastic reaction events in 60 days beam time in total.

In this proceedings, we will present the experimental plan of the scattering experiment and results of the detailed simulation studies.