Speaker
Description
In Universe there are many varieties of matter created by the strong interaction, such as hadrons,
nuclei and the very high density quark matter which might be formed inside a neutron star. Because
those particles and matter are generated by the strong interaction, the theory of strong interaction,
i.e. the Quantum Chromo dynamics(QCD), will give answers how those states are forming from
elementary particles, i.e. quarks and gluons.
One of the main questions in hadron physics is how the mass of the hadron is generated within
QCD. As we know that more than 98% of the hadron mass is generating dynamically via the
spontaneous breaking of chiral symmetry(χSB) in the QCD vacuum, therefore the properties of the
hadron should strongly be coupled with the order parameter of the χSB, i.e. the value of quark
condensati, < qq > ̄ .
One way to study this question is to investigate the properties of mesons inside nuclei, because
a partial restoration of the chiral symmetry is expected inside the high density environment, even
with normal nuclear matter, where the value of < qq > ̄ could be decreased compared with the value
in vacuum. Thus, if the origin of the hadron mass is indeed the χSB, a reduction of the hadron
mass or an attractive interaction between the meson and nuclei will appear. Here we are focusing
on the φ meson in nuclei studies.
There are experimental challenges to investigate the property of φ meson in nuclear matter. The
NA60 experiment at CERN presented the mass and width of the φ meson in high energy indium-
indium collisions as a function of collision centrality, which is equivalent to the energy density of
the created high temperature matter. The result shows that no clear modification of the φ meson
property inside a high temperature environment. On the other hand, KEK-PS E325 experiment
reported about 3.4% mass reduction of the φ meson in medium-heavy nuclei (Cu). This result is
possibly an indications of the partial restoration of chiral symmetry in nuclei, however, it is hard
to derive strong conclusions from the data.
If the mass of the φ mesons reduced in nuclei, it may indicate an attractive interaction between
φ meson and nucleus. If the attraction is strong enough, the formation of a φ meson nucleus
bound state is expected. Therefore, we are proposing a new experiment at J-PARC to search for
a φ-nucleus bound state and measure its binding energy, using ̄pp → φφ reaction as an elementary
process to produce slowly moving φ mesons. We demonstrate that a completely background-free
missing-mass spectrum can be obtained efficiently by spectroscopy together with K+Λ tagging.
This paper gives an overview of the physics motivation and detector concept, explains the direction
of the initial research and give the recent status of the detector development.
This presentation is an invited talk to the Session 7 of the conference.
