Spectroscopy of charmed baryons using hadron beam at J-PARC

Understanding hadron formation is one of the fundamental goals of hadron physics. It is essential way to investigate the effective degrees of freedom of hadrons with extended constituents such as the quark-quark correlation, namely the diquark correlation. In the case of light baryons, three pairs of diquarks are correlated with equal weight so that the diquark correlation cannot be extracted. When one quark in the baryon is replaced by a heavier quark called charm, the diquark correlation is expected to develop in the excited state of the charmed baryon. As a result, two excitation modes, called isotope shifts, appear in the level structure. The lambda- and rho-modes are the orbital excitation of the diquark and charm quark and the rotation of the diquark, respectively. These excited states are produced by the diquark correlation that could not be observed in lighter quark baryons. The study of the excitation spectra of charmed baryons allows us to investigate the lambda- and rho-excitation modes, which are strongly related to the internal structure of charmed baryons. The production and decay rates of charmed baryons [1] are expected to provide essential information for establishing the diquark correlation.

The charmed baryon spectroscopy experiment (E50) [2] is planned at the π20 beam line of the J-PARC Hadron Experimental Facility to reveal the structure of hadrons using the world's most intense meson beam. The π20 beam line, currently under construction, can deliver unseparated secondary beams with momentum up to 20 GeV/c at intensities above 10 MHz with a momentum resolution of 0.1%(sigma). High-momentum secondary beams with high-intensity and high-resolution can be used for the E50 experiment. In the experimental area, we will construct a large size magnetic spectrometer system which is designed to measure all charged particles produced by the pi- p → Yc*+ D*- reaction at 20 GeV/c and reconstructed the missing masses of the produced charmed baryons. From the measurement of the cross section, we can observe the charmed baryon states as missing masses with different yields depending on the lambda- and rho-excitation modes. Hadron beams are an essential tool for studying charmed baryon excited states, and J-PARC promotes important research in hadron physics.