Baryon-antibaryon pair production in time-dependent meson fields

Abstract

Strong mean meson fields, which are known to exist in normal nuclei, experience a violent deformation in the course of a heavy-ion collision at relativistic energies. This may give rise to a new collective mechanism of the particle production, not reducible to the superposition of elementary nucleon-nucleon collisions. We study the baryon-antibaryon (NN, AA, . . . ) pair production under some simplifying assumptions about the space and time variation of meson fields in the nuclear collision process. The mutual deceleration of nuclei is described schematically by introducing the time-dependent relative velocity. For comparison the yield of NN pairs is also calculated within a convolution model assuming the same deceleration scenario. Due to the specific Lorentz structure, the vector meson field turns out to be more efficient for producing pairs than the scalar field. Within the perturbative approach we study two processes: the bremsstrahlung of a virtual meson and the fusion of two virtual mesons, both leading to the baryon-antibaryon final states. The calculated multiplicities of NN and AA pairs grow fast with the bombarding energy, reaching a saturation above the RHIC energy ( v s = 200A GeV). At lower energies the coherent production mechanism gives higher pair yields than predicted by microscopic cascade-like models. The rapidity spectra of antibaryons exhibit a characteristic two-hump structure which may serve as an observable signature of the bremsstrahlung mechanism. A strong sensitivity of the predicted yield to the baryon effective mass and the parameters characterizing the stopping power of nuclear matter is demonstrated.PACS number(s): 25.75.+r, 13.75.Cs, 13.85.Ni, 21.65.+f

Particle emission following Coulomb excitation in ultrarelativistic heavy-ion collisions

“…The relative contributions to the inclusive cross sections from the double photon absorption, σ (2) i /(σ (1) i + σ (2) i ), are listed for the same reactions in Tab. 4.…”

“…The first category contains collisions with direct nuclear overlap. In addition to nucleon-nucleon or parton-parton collisions, which are the most obvious sources of secondary hadrons, collective mechanisms were considered for baryon-antibaryon pair [1] or dilepton [2] production. The second category deals with "distant" electromagnetic collisions without nuclear overlap.…”

“…Total cross sections (barn) of electromagnetic dissociation, σ ED , and contributions from the single, σ(1) , and double, σ(2) , photon absorption. The values are given for the present and future heavy-ion beams of Pb and Au nuclei.…”

Bremsstrahlung dileptons in ultrarelativistic heavy ion collisions

“…[10], we investigate whether this source could account for part of the observed enhancement of dilepton numbers as reported by CERES collaboration. In reference [10] only the production of ω mesons due to the deceleration and their subsequent decay into dileptons has been taken into account. This corresponds to considering the iso-scalar part of the electro-magnetic current.…”

“…production of ρ-mesons and their subsequent decay into dileptons. These two amplitudes, iso-scalar and iso-vector, interfere destructively and as a result the dilepton production cross section from the coherent deceleration scales like the square of the charge and not the square of the baryon number, as assumed in [10]. We should also note that the point like limit of this process addressed here has been considered in [11].…”