Dileptons from disoriented chiral condensates

Abstract

Disoriented chiral condensates or long wavelength pionic oscillations and their interaction with the thermal environment can be a significant source of dileptons. We calculate the yield of such dilepton production within the linear sigma model, both in a quantal mean-field treatment and in a semi-classical approximation. We then illustrate the basic features of the dilepton spectrum in a schematic model. We find that dilepton yield with invariant mass near and below 2m π due to the soft pion modes can be up to two orders of magnitude larger than the corresponding equilibrium yield.

Disoriented chiral condensate: Theory and experiment

“…It has been proposed that anomalous pion production from a DCC would result in anomalous radiation of low-momentum photon and/or low-mass dileptons [125,126,127,128,129]. Here we illustrate these ideas in the case of dilepton production.…”

“…To illustrate the anomalous electromagnetic emission due to a DCC, we essentially follow the schematic model presented in [126,127]. The presence of a DCC may be modeled by splitting the pion field operators into a classical part π cl (x), which represent the coherent DCC excitation, and the restπ(x), which describes the background pions:…”

“…Another possibility, suggested in Ref. [127], is that non-coherent pions from the surrounding heat bath may annihilate on the coherent DCC state, forming dilepton pairs of typical invariant masses in a rather narrow window around M ≃ 2m π , thus avoiding the π 0 Dalitz-decay region. The corresponding contribution to the dilepton rate (168) comes from the second term on the RHS side of Eq.…”

Lifetime of a Disoriented Chiral Condensate

“…Considering the entire hadronic phase exists for about 10 − 20 fm/c, the DCC could live for a substantial fraction of the hadronic phase, allowing for a strong signal of its existence, e.g. in the dilepton channel [9]. Even assuming three times the number of thermal pions, as predicted by some event generators [10], the half-life is still τ = 3.8 fm/c at T = 150 MeV.…”

“…2, which shows the half-life is between 3 and 3.5 fm/c for all the pion to nucleon ratios considered. If the over-population of particle spectra predicted by event generators is correct, it implies the DCC signal would be difficult to detect from hadronic observables, requiring an indirect means such as dileptons [9].…”