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HK: Fachverband Physik der Hadronen und Kerne

HK 2: Heavy Ion Collision and QCD Phases I

HK 2.3: Vortrag

Montag, 14. März 2016, 14:45–15:00, S1/01 A01

The electromagnetic N-Δ transition form factor and its impact on dilepton spectra — •Janus Weil¹, Gilberto Ramalho², Teresa Pena³, Hendrik van Hees¹, and Ulrich Mosel⁴ — ¹Frankfurt Institute for Advanced Studies — ²Federal University of Rio Grande do Norte — ³Universidade de Lisboa — ⁴Universität Giessen

The Dalitz decay of Δ→ Ne⁺e⁻ represents an important contribution to inclusive dilepton spectra. However, unlike the mesonic Dalitz decays, the transition form factor in this decay is not very well-constrained so far. There is plenty of electron-scattering data to fix the tails of the form factor in the space-like regime, but the more interesting region is certainly the time-like regime, where one expects to find one or more vector-meson poles. However, the only experimental constraints in the time-like regime come from dilepton spectra, which are not straightforward to interpret, in particular since they contain contributions from several other processes (including N^* and Δ^* decays) that need to be disentangled from each other. We discuss different models for the N-Δ transition form factor, including a simple VMD-like approach and a covariant spectator quark model, where one distinguishes contributions from a bare quark core and a meson cloud. These form-factor models are then coupled with a hadronic transport model, in order to simulate the dynamics of pp and heavy-ion collisions and compute inclusive dilepton spectra. By comparing those to data measured with the HADES detector, we obtain constraints on the N-Δ transition form factor and discuss their implications.