We propose to measure the strong-interaction induced energy shift of the 3d -> 2p X-ray transition of kaonic helium-3 atoms with a precision better than 2 eV at the J-PARC 50-GeV PS. The proposed experiment, analyzed together with that for kaonic helium 4 atoms measured by the KEK-PS E570 collaboration, will provide crucial information on the isospin-dependent antikaon-nucleus strong interaction at the low energy limit, and will provide decisive data to understand the basis of the prediction of deeply-bound kaonic nuclei, and to clarify the nature of the strange multibaryon candidates recently reported at KEK, DAFNE and BNL. The major parameters of the proposed experiment are summarized below:

    reaction : stopped K- + 3He -> hv(~ 6.4 keV) + X,
    primary beam: 30 GeV, 9 ╬╝A proton,
    secondary beam: 0.75 GeV/c K-,
    J-PARC beamline: K1.8BR or K1.1,
    target: Liquid He-3, X-ray detectors: 8 x 100 mm2 silicon drift detectors (SDD).

The anticipated beam time consists of 10 days for commissioning and 3.5 days at K1.8BR (assuming full PS intensity) and 35 days at K1.8BR (with 10% of the design intensity) respectively.

The present proposal is closely related to another proposal to the J-PARC 50-GeV PS, "A search for deeply-bound kaonic nuclear states by in-flight 3He(K-,n) reaction". Both experiments will use the same beamline and the same 3He target. In view of the relative simplicity of the X-ray measurement and its modest beam requirement, we believe it is appropriate to execute the present X-ray proposal before the "in-flight" experiment. The proposed experiment will be ready on DAY-1, and can quickly deliver crucial physics results. It is hence most suited as the J-PARC DAY-1 experiment. 

Funded by:

FWF Project P20651-N20