There are electrons and nuclei in the atom, and the nuclei are composed of protons and neutrons.When protons and neutrons are divided, they become quarks, which are elementary particles.Since electrons are negligibly lighter than other particles, the mass of an atom seems to be the sum of quark masses.
However, in reality, it is 100 times heavier.Dr. Yoichiro Nambu, who won the Nobel Prize in Physics in 2008, thought that this was because "quark condensation" was clinging to quarks.

　Quark condensation is a state in which quarks and antiquarks are paired and condensed in a vacuum.Although it did not exist in the high temperature and high density state immediately after the creation of the universe, it is said that it occurred in the process of the universe expanding and cooling.

　The key to demonstrating the existence of quark condensation is the precise measurement inside the nucleus.The density inside the nucleus is about 100 trillion times that of water, and it is expected that the amount of quark condensation will decrease as it did immediately after the creation of the universe.Therefore, this research group worked on the precise measurement of "pion atom" in which a pion having a mass 300 times that of an electron is bound to the nucleus.Since pions take an orbit that rubs the surface of the nucleus, detailed examination of this can provide information on the inside of the nucleus.

　And this time, using the world's highest intensity accelerator, which RIKEN is proud of, we succeeded in obtaining a large amount of pion atom data with time efficiency several tens of times higher than before.As a result, the next step aims to determine the reduction rate of quark condensation in the nucleus with high accuracy from more data.

Paper information:[Physical Review Letters] Spectroscopy of pionic atoms in 122Sn (d, 3He) reaction and angular dependence of the formation cross sections