Gaitanos, T.

Lenske, H.

GSI Repository

In-Medium strangeness dynamics at PANDA∗T. Gaitanos1 and H. Lenske1,21Inst. fu¨r Theor. Physik, Universita¨t Giessen, Germany; 2GSI Darmstadt, GermanyHypernuclear physics opens a unique opportunity to ex-plore the hyperon-nucleon (Y N ) and the hyperon-hyperon(Y Y ) in-medium interactions at terrestrial laboratories.Such studies are important for a better understanding ofthe in-medium interactions with strangeness degree of free-dom, which is still uncertain, but of relevance for nuclearastrophysics [1]. The experimental knowledge on multi-strangeness hypernuclei has been so far scarce. However,recent experiments at GSI are very promising. In the Hy-pHI [2] experiment precise production rates of single-Λ(S = −1) hypernuclei were measured. An abundant pro-duction of double-Λ (S = −2) clusters is also expected inthe PANDAexperiment [3] at FAIR.We investigate theoretically the multi-strangeness dy-namics within the Giessen-BUU (GiBUU) approach [4]. Inparticular, we have studied antiproton-induced reactions al-lowing for reactions of the secondary Ξ-beam on a secondtarget. The formation of double-Λ hypernuclei occurs inthe Ξ-interaction with the second target [5]. Two issuesare of importance for the production of double-strangenesshypermatter, see Fig. 1. At first, the absorption of the Ξ-beam inside the target matter decreases with increasing en-ergy. This is due to the strong decrease of the elemen-tary ΞN → ΛΛ channel [5]. Secondly, the abundance ofbound Λ-hyperons also strongly decreases with rising inci-dent Ξ-energy. This is mainly due to the repulsive vectorfield which becomes more pronounced as the particle en-ergy increases. These effects lead to a rather strong energydependent rise of the double-Λ hypernuclear productioncross section. Thus low-energetic cascade beams shouldbe used at PANDAin order to obtain high production ratesof double-strangeness hyperfragments [5].So far bare interactions for elementary Y N, Y Y -channels have been used in transport approaches. However,at PANDAthe strangeness dynamics takes place at densi-ties closely up to saturation. We have studied in-mediumeffects on various Y N -processes by solving the Lippmann-Schwinger equation with a Pauli-exclusion operator forintermediate states as the leading-order in-medium ef-fect [6, 7]. The elementary Y N cross sections are indeedinfluenced by in-medium effects, in particular, at low en-ergies, as shown in Fig. 2 (similar effects occur for quasi-elastic channels with strangeness exchange).In the S=-2 sector the situation is still very controversialtheoretically [8]. Presently we are investigating the influ-ence of various calculations on S=-2-channels [9] on thestrangeness production in p¯-induced reactions and extend-ing our studies to the S=-3 sector by accounting for the∗Work supported by BMBF, DFG, HIC for FAIR, and GSI-JLUGiessen collaboration agreement0 50 100 150time [fm/c]00.20.40.60.81NΞ,Λ (t)50 100 150time [fm/c]50 100 150time [fm/c]ΛallΛfreeΞEkinΞ = 0.15 GeV EkinΞ = 0.3 GeVEkinΞ = 0.5 GeVFigure 1: GiBUU results for the time dependence of alland free Λs and of Ξs for central Ξ-induced reactions onCu-target at beam energies as indicated [5].formation of Ω-baryons [10]. The preliminary results arevery promising concerning a possible formation of multi-strangeness bound systems at PANDA. We emphasize therelevance of our theoretical results for the future activitiesat FAIR.0 100 200 300 400Tlab [MeV]050100150200σ [mb]ρ=0ρ=0.08 [fm-3]ρ=0.16 [fm-3]100 200 300 400Tlab [MeV]Λp -> Λp Σ+n -> Σ+nFigure 2: . Energy dependence of elastic in-medium crosssections for ΛN and ΣN scattering at various densities asindicated [7].References[1] J. Schaffner, I. Mishustin, Phys. Rev. C53 (1996) 1416.[2] C. Rappold, et al., Nucl. Phys. A622 (2010) 231.[3] A.S. Lorente, et al., Phys. Lett. B 697 (2011) 222.[4] O. Buss, et al., Phys. Rep. 512 (2012) 1.[5] T. Gaitanos, et al., Nucl. Phys. A881 (2012) 240.[6] T. Gaitanos, et al., Nucl. Phys. A914 (2013) 405.[7] A. Obermann, Masters Thesis, 2011, Univ. Giessen, unpub-lished.[8] J.K. Ahn, et al., Phys. Lett. B 633 (2006) 214.[9] T.A. Rijken, Y. Yamamoto, nucl-th/0608074; Y. Fujiwara, etal., Phys. Rev. C64 (2001) 054001.[10] T. Gaitanos, et al., in preparation.GSI SCIENTIFIC REPORT 2013 THEORY-25doi:10.15120/GR-2014-1-THEORY-25 277

In-Medium strangeness dynamics at PANDA

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In-Medium strangeness dynamics at PANDA

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