Search

By extending the $$\Phi $$ -derivable approach in the Nambu-Jona-Lasinio model to a finite magnetic field we calculate the properties of pion, $$\sigma $$ , and $$\rho $$ mesons in a magnetic field at finite temperature not only in the quark-antiquark bound state scheme but also in the pion-pion scattering resonant state scenario. Our calculation as a result makes manifest that the masses of $$\pi ^{0}$$ and $$\sigma $$ meson can be nearly degenerate at the pseudo-critical temperature which increases with increasing magnetic field strength, and the $$\pi ^{\pm }$$ mass ascends suddenly at almost the same critical temperature. Meanwhile the $$\rho $$ mesons' masses decrease with the temperature but increase with the magnetic field strength. We also check the Gell-Mann-Oakes-Renner relation and find that the relation can be violated clearly with increasing temperature, and the effect of the magnetic field becomes pronounced around the critical temperature. With different criteria, we analyze the effect of the magnetic field on the chiral phase transition and find that the pseudo-critical temperature of the chiral phase cross, $$T_\mathrm{c}^{\chi }$$ , is always enhanced by the magnetic field. Moreover, our calculations indicate that the $$\rho $$ mesons will get melted as the chiral symmetry has not yet been restored, but the $$\sigma $$ meson does not disassociate even at very high temperature. Particularly, it is the first to show that there does not exist a vector meson condensate in the QCD vacuum in the pion-pion scattering scheme. [ABSTRACT FROM AUTHOR]

We present experimental results on inclusive spectra and mean multiplicities of negatively charged pions produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/ c ( $$\sqrt{s} = $$ 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively). The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN super proton synchrotron. Two-dimensional spectra are determined in terms of rapidity and transverse momentum. Their properties such as the width of rapidity distributions and the inverse slope parameter of transverse mass spectra are extracted and their collision energy dependences are presented. The results on inelastic p+p interactions are compared with the corresponding data on central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. The results presented in this paper are part of the NA61/SHINE ion program devoted to the study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter. They are required for interpretation of results on nucleus-nucleus and proton-nucleus collisions. [ABSTRACT FROM AUTHOR]

We study the three-pion decays of the lightest isoscalar vector mesons, ω and ɸ, in a dispersive framework that allows for a consistent description of final-state interactions between all three pions. Our results are solely dependent on the phenomenological input for the pion-pion P-wave scattering phase shift. We predict the Dalitz plot distributions for both decays and compare our findings to recent measurements of the ɸ→3π Dalitz plot by the KLOE and CMD-2 collaborations. Dalitz plot parameters for future precision measurements of ω→3π are predicted. We also calculate the ππ P-wave inelasticity contribution from ωπ intermediate states. [ABSTRACT FROM AUTHOR]

We perform an analysis of the form factors that rule the structure-dependent amplitude in radiative pion decay. The resonance contributions to π→eνeγ decays are computed through the proper construction of the vector and axial-vector form factors by setting the QCD driven asymptotic properties of the three-point Green functions 〈VVP〉 and 〈VAP〉, and by demanding the smoothening of the form factors at high transfer of momentum. A comparison between theoretical and experimental determination of the form factors is also carried out. We also consider and evaluate the role played by a non-standard tensor form factor. We conclude that, at present and due to the hadronic uncertainties, the search for new physics in this process is not feasible. [ABSTRACT FROM AUTHOR]

We analyze a pion form factor formulation which fulfills the Analyticity requirement within the redden Local Symmetry (HLS) Model. This implies an s-dependent dressing of the p - γ VMD coupling and an account of several coupled channels. The corresponding function Fπ (s) provides nice fits of the pion form factor data from s = -0.25 to s = 1 GeV2. It is shown that the coupling to K&Kmacr; has little effect, while ωπ0 improves significantly the fit probability below the φ mass. No need for additional states like ρ(1450) shows up in this invariant-mass range. All parameters, except for the subtraction polynomial coefficients, are fixed from the rest of the HLS phenomenology. The fits show consistency with the expected behaviour of Fπ(s) at s = 0 up to O(s2) and with the phase shift data on δ11(s) from threshold to somewhat above the φ mass. The ω sector is also examined in relation with recent data from CMD-2. [ABSTRACT FROM AUTHOR]