Recent progress of hyperon-nucleon scattering experiment and future prospects for ΛNN interaction study at J-PARC*

Scattering experiments involving a hyperon and a proton are the most effective way for investigating 2 body hyperon–nucleon (YN) interactions, as is the case in various intensive studies on pp and np scattering for understanding nucleon–nucleon (NN) interactions. Scattering observables, such as differential cross sections and spin observables, are essential experimental inputs for constructing theoretical frameworks of YN interactions assuming a broken flavor SU(3) symmetry. 

A new hyperon–proton scattering experiment, dubbed J-PARC E40, was performed to measure differential cross sections of the Σ^-p, Σ⁺p elastic scatterings and the Σ^-p→Λn scattering by identifying a lot of Σ particles in the momentum region ranging from 0.4 to 0.8 GeV/c produced by π^±p→K⁺X reaction. We successfully measured the differential cross sections of these three channels with a drastically improved accuracy with a fine angular step. Especially, we derived the phase shift of the ³S₁ channel of the Σ⁺p channel to be from -20 to -35 degrees for 440 - 800 MeV/c Σ⁺ momentum for the first time. 

Following this success, we proposed a new experiment to measure the differential cross sections and spin observables by using a highly polarized Λ beam for providing quantitative information on the ΛN interaction. The realistic ΛN interaction is essential to understand not only the Λ hypernuclei but also neutron stars.  Such realistic ΛN interaction is also essential to extract the ΛNN three-body force in the Λ hypernuclei. We have also proposed the high-resolution Λ hypernuclear spectroscopy via the (π⁺, K⁺) reaction over a wide mass range by using the dedicated high-resolution beam line (HIHR). These two experiments are the flag ships of hypernuclear physics program at the extended hadron hall, which will be constructed in near future.

In this presentation, we will present the measured differential cross sections of three Σp channels and future prospects of hypernuclear physics at J-PARC.