Pseudoscalar mesons in hot, dense matter

Abstract

Phase transitions in hot and dense matter and the in-medium behavior of pseudoscalar mesons (π ± , π 0 , K ± , K 0 ,K 0 , η and η ′ ) are investigated, in the framework of the three flavor NambuJona-Lasinio model, including the 't Hooft interaction, which breaks the U A (1) symmetry. Three different scenarios are considered: zero density and finite temperature, zero temperature and finite density in quark matter with different degrees of strangeness, and finite temperature and density.At T = 0, the role of strange valence quarks in the medium is discussed, in connection with the phase transition and the mesonic behavior. It is found that the appearance of strange quarks, above certain densities, leads to meaningful changes in different observables, especially in matter with β -equilibrium. The behavior of mesons in the T − ρ plane is analyzed in connection with possible signatures of restoration of symmetries.

Search for η′ Mesic Nuclei in GSI/FAIR

“…A large mass reduction is expected for η ′ accommodated in the nuclear medium [7,8,23]. Since the mass difference between η ′ and η mesons is expected to vanish at full restoration of the chiral symmetry [24,25], the partial restoration in nuclear medium at a level of ∼ 30% as deduced in the pionic atom spectroscopy results in substantial modification of the η ′ mass.…”

“…An overall explanation of the origin will certainly lead to an 1 understanding of the non-perturbative aspects of low-energy region of the Quantum ChromoDynamics (QCD) [2]. In this context, the η ′ meson has an extremely large mass and its origin stimulates theoretical and experimental studies [3][4][5][6][7][8][9][10][11]. Theoretically the large mass is interpreted in terms of the interplay between the chiral symmetry breaking and the axial U(1) anomaly [8,12,13].…”

Excitation Spectra of Carbon Nuclei near \(\eta '\) Emission Threshold

“…In nuclear medium where the chiral symmetry is partly restored, a large mass reduction of the η ′ is expected by theories [7,10,14]. The predicted mass reduction at normal nuclear density depends on theoretical models and ranges from 37 to 150 MeV/c 2 [7,9,15].…”

“…The predicted mass reduction at normal nuclear density depends on theoretical models and ranges from 37 to 150 MeV/c 2 [7,9,15]. Experimentally incident energy dependence of the η ′ photo-production cross section on a carbon nucleus near the η ′ production threshold was measured in the CB-ELSA/TAPS experiment indicating the real part of the potential to be −37 ± 10 ± 10 MeV [16].…”

“…Comprehensive understanding of the origin of the widely distributed masses will contribute to understanding of the QCD [2]. Among the mesons in the lowest-mass pseudo-scalar nonet, the η ′ has much larger mass than the others and its origin has been stimulating many theoretical and experimental studies [3][4][5][6][7][8][9][10][11]. Theoretically, axial U(1) anomaly constitutes an important part of the mechanism of the large mass in combination with spontaneous breakdown of chiral symmetry [10,12,13].…”