https://doi.org/10.1140/epja/i2013-13034-7
Regular Article - Experimental Physics
Deep sub-threshold K*(892)0 production in collisions of Ar + KCl at 1.76 A GeV
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Instituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, 95125, Catania, Italy
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LIP-Laboratório de Instrumentação e Física Experimental de Partículas, 3004-516, Coimbra, Portugal
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Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30-059, Kraków, Poland
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GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
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Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, 01314, Dresden, Germany
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Joint Institute of Nuclear Research, 141980, Dubna, Russia
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Institut für Kernphysik, Johann Wolfgang Goethe-Universität, 60438, Frankfurt, Germany
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II.Physikalisches Institut, Justus Liebig Universität Giessen, 35392, Giessen, Germany
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Istituto Nazionale di Fisica Nucleare, Sezione di Milano, 20133, Milano, Italy
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Institute for Nuclear Research, Russian Academy of Science, 117312, Moscow, Russia
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Physik Department E12, Technische Universität München, 85748, München, Germany
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Department of Physics, University of Cyprus, 1678, Nicosia, Cyprus
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Institut de Physique Nucléaire (UMR 8608), CNRS/IN2P3 - Université Paris Sud, F-91406, Orsay Cedex, France
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Nuclear Physics Institute, Academy of Sciences of Czech Republic, 25068, Rez, Czech Republic
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Departamento de Física de Partículas, Univ. de Santiago de Compostela, 15706, Santiago de Compostela, Spain
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Instituto de Física Corpuscular, Universidad de Valencia-CSIC, 46971, Valencia, Spain
* e-mail: kotte@hzdr.de
Received:
10
December
2012
Accepted:
6
February
2013
Published online:
15
March
2013
Results on the deep sub-threshold production of the short-lived hadronic resonance K*(892)0 are reported for collisions of Ar + KCl at 1.76A GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The K*(892)0 production probability per central collision of and the K*(892)0/K0 ratio of
are determined at the lowest energy so far (i.e. deep below the threshold for the corresponding production in nucleon-nucleon collisions,
MeV). The K*0/K0 ratio is compared with results of other experiments and with the predictions of the UrQMD transport approach and of the statistical hadronization model. The experimental K*0 yield and the K*0/K0 ratio are overestimated by the transport model by factors of about five and two, respectively. In a chemically equilibrated medium the ratio corresponds to a temperature of the thermalized system being systematically lower than the value determined by the yields of the stable and long-lived hadrons produced in Ar + KCl collisions. From the present measurement, we conclude that sub-threshold K* production either cannot be considered to proceed in a system being in thermal equilibrium or these short-lived resonances appear undersaturated, for example as a result of the rescattering of the decay particles in the ambient hadronic medium.
© SIF, Springer-Verlag Berlin Heidelberg, 2013