| 研究実績の概要 |
The purpose of this research project was to relate the mass change of the phi meson in nuclear matter with experimental data obtained by measuring the dilepton (an electron and positron pair) spectrum generated from pA (proton-nucleus) collisions, making use of realistic numerical transport simulations of these reactions. The mass change can then be related to the chiral symmetry properties of the strong interaction in vacuum and at finite density and can thus help our understanding of the generation of hadron masses.
During the project period, an existing transport simulation code was adapted to the study of the phi meson in nuclear matter through pA reactions. Using this code to simulate the relevant pA reactions, it was found that the dilepton data extracted from 12 GeV pA reactions at KEK can be interpreted as a phi meson which has a large negative mass shift in nuclear matter. To be compatible with the data, this mass shift however has to vanish as the lab frame momentum increases to values of above 1 GeV/c.
This result, in combination with earlier QCD sum rule calculations, means that the strange quark chiral condensate is strongly reduced in nuclear matter. This finding, however, is in conflict with recent lattice QCD results, which predict a smaller change of the condensate. Therefore, more precise data (for example from from the recently started J-PARC E16 experiment) will be needed to make the finding of this work more conclusive.
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