Abstract
A novel type of diagnostics for dense and/or hot nuclear matter produced in heavy-ion collisions at NICA and similar future colliders (FAIR, etc.) is suggested. The diagnostics is based on an assumption (confirmed in many experiments worldwide) about intensive generation of light scalar mesons (σ ) the consequent decay of which produces γγ pairs with the mass and width dependent upon density and temperature of the fireball produced in the collision process. Thus, measurements of the absolute yield, mass and width of the γγ signal carry valuable information about the state of fireball generated during the high-energy nuclear collision.
Highlights
Chiral symmetry restoration in hot and/or dense nuclear matterOne of the main goals of the future heavy-ion collider NICA in Dubna will be the search for signals of the phase transition between hadronic matter and quark-gluon plasma and search for new phases of baryonic matter, including the mixed phase
There is a key hypothesis about partial chiral symmetry restoration (CSR) in hot and/or dense nuclear matter inside the fireball, which is a consequence of basic principles of QCD
One can suggest the possible reason for such a large spread of σ-meson parameters to be big errors arising when extracting the σ mass and width from experimental data but the really different values of the σ basic parameters found in various hadronic processes
Summary
One of the main goals of the future heavy-ion collider NICA in Dubna will be the search for signals of the phase transition between hadronic matter and quark-gluon plasma and search for new phases of baryonic matter, including the mixed phase. The CSR effect can be observed in two areas: (i) in a single hadron when it gets to be highly excited [1, 2] and (ii) in hot and/or dense nuclear matter, i.e., in medium [3,4,5,6]. When the nuclear (quark) matter density becomes sufficiently high, the Pauli principle or temperature destroys the qqcondensate, the valence quark motion is liberated from the condensate, and the CSR happens. This effect is rather similar to disappearance of superconductivity in electron gas in metals when the temperature is rising, since Cooper pairs are destroyed. The overall importance of CSR can be concluded from the citation [3]: “Observing the restoration of chiral symmetry at finite temperature is one of the central aims in the future relativistic heavy-ion experiments at the BNL RHIC and CERN LHC”
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