Chungsik Song

Thermal effects on dilepton production from π-π annihilation

Abstract We study finite temperature effects on dilepton production from pion-pion annihilation in hot hadronic matter. The softening of the pion dispersion relation in a medium is found to enhance the production rate of dileptons with invariant masses in the region of 2m π ∗ (T) ϱ . On the other hand, the reduction of the pion electromagnetic form factor at finite temperature leads to a suppression of the dilepton production rate. Including both effects, we have found that the dilepton yield is slightly enhanced in the invariant mass region M = 270 ∼ 600 MeV but is suppressed around the vector meson resonance. We further discuss the relevance of our results to recent experimental data from the S+Au collisions at CERN/SPS energies by the CERES Collaboration.

Properties of vector mesons at finite temperature: Effective Lagrangian approach.

We examine the properties of {rho} mesons at finite temperature {ital T} with the use of an effective chiral Lagrangian. The effective Lagrangian includes vector and axial-vector mesons as massive Yang-Mills fields of the chiral symmetry. It is shown that at the leading order of the temperature the effective mass of the {rho} meson is not changed and only a mixing in vector and axial-vector correlators takes place. {copyright} {ital 1996 The American Physical Society.}

Effective mass and width of pions at T ≠ 0

Abstract We calculate the effective mass and thermal width of the pions in hot hadronic matter based on an effective chiral lagrangian. The lagrangian includes the vector and axial-vector mesons explicitly. The effective mass is obtained from the pole position of the pion propagator at finite temperature and the inverse of the screening length. The results obtained from both cases decrease with temperature but are different numerically. The thermal width of the pion is computed from the imaginary part of the pion self-energy in the medium. The width is almost negligible at low temperatures but increases rapidly with temperature at T s

Role of the a1 meson in dilepton production from hot hadronic matter

100 MeV .

Dilepton production from resonance scattering in hot hadronic matter.

Dilepton production from hot hadronic matter is studied in an effective chiral Lagrangian with pions, [rho] mesons, and [ital a][sub 1] mesons. We find that the production rates from reactions that involve axial-vector mesons dominate over contributions from all other reactions when the dilepton invariant mass is above 1.5 GeV.

Photon emission from hot hadronic matter described by an effective chiral Lagrangian

Dilepton production from resonance scattering in hot hadronic matter is studied. Including the widths of these resonances, which enhance the phase space for dilepton production, we find that the production rate is significantly increased if a resonance appears in the extended phase space. For the reaction {pi}+{rho}{r_arrow}{ital l}{sup +}+{ital l}{sup {minus}}, the finite {rho} meson width extends the invariant mass below the {omega}-meson mass, so a peak at the {omega}-meson mass is seen in the dilepton spectrum. Similarly, a {rho}-meson peak appears in the reaction {rho}+{rho}{r_arrow}{ital l}{sup +}+{ital l}{sup {minus}}. On the other hand, the effect of particle widths in the reaction {pi}+{ital a}{sub 1}{r_arrow}{ital l}{sup +}+{ital l}{sup {minus}} is small since the extended phase space does not include any resonance. {copyright} {ital 1996 The American Physical Society.}