Abstract
The High-Acceptance DiElectron Spectrometer (HADES) operates in the 1 - 2A GeV energy regime in fixed target experiments to explore baryon-rich strongly interacting matter in heavy-ion collisions at moderate temperatures with rare and penetrating probes. We present results on the production of strange hadrons below their respective NN threshold energy in Au+Au collisions at 1.23A GeV ([see formula in PDF] = 2.4 GeV). Special emphasis is put on the enhanced feed-down contribution of ϕ mesons to the inclusive yield of K- and its implication on the measured spectral shape of K-. Furthermore, we investigate global properties of the system, confronting the measured hadron yields and transverse mass spectra with a Statistical Hadronization Model (SHM) and a blastwave parameterization, respectively. These supplement the world data of the chemical and kinetic freeze-out temperatures.
Highlights
The first data on sub-threshold K− production in Heavy-Ion Collisions (HIC) obtained by the KaoS collaboration revealed that the K− and K+ multiplicities show, despite their different NN threshold energies, a similar increase with collision centrality, whereas the transverse mass spectra of K− are significantly softer compared to the ones of K+
These two observations found a possible explanation within transport model calculations when assuming the strangeness exchange reaction Λπ → NK−, which was predicted by Ko in the early 1980ies [16] to be the dominant production channel for K− below threshold [17]
Recent data on strangeness production in smaller collision systems indicate that φ feed-down decays constitute a sizeable source for K− production below the threshold [18,19,20], which was not taken into account in transport models
Summary
The first data on sub-threshold K− production in HIC obtained by the KaoS collaboration revealed that the K− and K+ multiplicities show, despite their different NN threshold energies, a similar increase with collision centrality, whereas the transverse mass spectra of K− are significantly softer compared to the ones of K+ (for a review of the data see [15]) These two observations found a possible explanation within transport model calculations when assuming the strangeness exchange reaction Λπ → NK−, which was predicted by Ko in the early 1980ies [16] to be the dominant production channel for K− below threshold [17].
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