虎扑电竞 虎扑电竞

An international collaboration led by Prof. S.N. Nakamura (Graduate School of Science, Tohoku University), Prof. J. Pochodzalla, Dr. P. Achenbach (Mainz University) and Prof. L. Tang (Hampton University) has been developing a new experimental technique - the decay-pion spectroscopy of electro-produced hypernuclei since 2011. This technique observes pions from two-body weak-decay of hypernuclei to measure precise masses of hypernuclei.

In a world first, the international collaboration used this new technique to successfully measure the mass of , which consists of one proton, two neutrons and one Λ particle.

The best resolution, 540 keV(FWHM), of the mass measurement of hypernuclei was achieved at the Jefferson Lab (USA) for using the (e,e'K⁺) reaction by the international collaboration led by Profs. Nakamura and Tang.
However the achieved resolution by this new method is 150 keV(FWHM) which is more than three times better than the previous world record.

The result was published in Physical Review Letters on June 9, 2015 (DOI: 10.1103/PhysRevLett.114.232501). This new measurement will contribute greatly to solving the puzzle of the Charge Symmetry Breaking of the Λ-N interaction.
Young researchers supported by the Japan Society for the Promotion of Science (JSPS) - the Strategic Young 虎扑电竞ers Overseas Visit　Program for Accelerating Brain Circulation (R2201) and Core-to-Core program (21002) - played essential roles in the success of this project.

Fig 1: A photo of A1 experimental hall of MAMI, Mainz University. Two large magnetic spectrometers (red and green) measure pions from decay of hypernuclei and another spectrometer (purple) tags kaons to select the events from hypernuclei.

Fig 2: Pion momentum distribution tagged by kaons. A characteristic peak with the momentum of 133MeV/c from two-body decay of was clearly observed.