Berger-Chen, J.-C.

Fabbietti, L.

Lapidus, K.

GSI Repository

Kaon in-medium potential probed in proton-nucleus reactions∗J.-C. Berger-Chen1,2, L. Fabbietti1,2, K. Lapidus†1,2 for the HADES collaboration1Physik Department E12, TU Mu¨nchen, James-Franck-Str. 1, 85748 Garching, Germany; 2Excellence Cluster“Universe”, TU Mu¨nchen, Boltzmannstr. 2, 85748 Garching, GermanyInsight into the fundamental properties of the strong in-teraction in the low energy domain — confinement andbroken chiral symmetry — might be gained with measure-ments of hadron in-medium properties. Of particular in-terest in this context are light vector mesons (ρ, ω, φ) and(anti)kaons. Modifications of the kaon (K+, K0) spectralfunction in a baryonic environment do not show substantialbroadening and are characterized by a positive and den-sity dependent mass shift reaching 25-35 MeV at nuclearground state density [1].A number of experiments recently addressed this issueand deduced a repulsive potential of 25 to 40 MeV basedon a comparison of data to microscopic transport modelcalculations [2, 3]. Thus, the magnitude of the kaon poten-tial remains unsettled in spite of relative simplicity of theunderlying kaon-nucleon interaction.The HADES collaboration addressed the issue ofthe momentum-dependent kaon potential with the high-statistics data on neutral kaon production (reconstructedvia the short-lived component K 0S) collected in proton-niobium collisions at a beam energy of 3.5 GeV. As a refer-ence measurement data obtained in proton-proton reactionsat the same beam energy have been used.Kinematical distributions of kaons were measured in abroad region of the phase space. Figure 1 shows the (ef-ficiency corrected and normalized) transverse momentumspectrum in a selected rapidity bin (the complete rapidityspan amounts to yCM ∈ (−0.85, 0.35)).The effect of the kaon potential as follows from ChPTwas studied by comparing the data to results obtained withthe GiBUU transport model [4], parameters of which (kaonproduction cross sections) were tuned to reproduce the ref-erence proton-proton measurement. Two sets of calcula-tions (with and without the kaon potential) are shown inFig. 1. The strength of the ChPT potential at normal nu-clear density for the kaon at rest is ≈ 35 MeV.The comparison was done in all rapidity bins and theagreement of the experimental data with the transportmodel simulations was quantified by means of a χ2-analysis. Simulations including the ChPT potential delivera significantly lower χ2 value as compared to calculationswithout potential. Moreover, and this is a distinct featureof the present study, variations of the uncertain parametersof the model (such as, for example, kaon yield in neutron-proton reactions) have been performed. For each set ofphysical parameters, calculations that include the potential∗Work supported by BMBF and the Excellence Cluster “Universe”.† kirill.lapidus@ph.tum.deFigure 1: K0 transverse momentum spectrum recon-structed in proton-niobium collisions in a selected rapid-ity bin. Experimental data are shown with black markers.GiBUU calculations without and with the kaon ChPT po-tential are shown by dashed and solid curve, respectively.consistently result in lower χ2-values.To summarize, the K0 kinematical distributions recon-structed in proton-niobium collisions favour the GiBUUtransport model calculations that incorporates the ChPTprediction for the potential.References[1] C. L. Korpa and M. F. M. Lutz, Acta Phys. Hung. A 22, 21(2005) [nucl-th/0404088].[2] M. L. Benabderrahmane et al. [FOPI Collaboration], Phys.Rev. Lett. 102 (2009) 182501 [arXiv:0807.3361 [nucl-ex]].[3] G. Agakishiev et al. [HADES Collaboration], Phys. Rev. C82, 044907 (2010) [arXiv:1004.3881 [nucl-ex]].[4] O. Buss, T. Gaitanos, K. Gallmeister, H. van Hees,M. Kaskulov, O. Lalakulich, A. B. Larionov, T. Leit-ner, J. Weil and U. Mosel, Phys. Rept. 512, 1 (2012)[arXiv:1106.1344 [hep-ph]].NQM-HADES-02 GSI SCIENTIFIC REPORT 20132 doi:10.15120/GR-2014-1-NQM-HADES-02

Kaon in-medium potential probed in proton-nucleus reactions

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Kaon in-medium potential probed in proton-nucleus reactions

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