Fabbietti, L.

Lapidus, K.

Scordo, A.

GSI Repository

Charged kaon production in pion-nucleus reactions at 1.7 GeV/c∗L. Fabbietti1,2, K. Lapidus†1,2, A. Scordo3, and the HADES collaboration1Physik Department E12, Technische Universita¨t Mu¨nchen, 85748 Garching, Germany; 2Excellence Cluster ’Origin andStructure of the Universe’ , 85748 Garching, Germany; 3INFN Laboratori Nazionali di Frascati, 00044 Frascati (Roma),ItalyThe production of strangeness in pion-nucleus reactionsallows to probe effects of cold nuclear matter, such asthe modification of the hadron spectral functions at zerotemperature and normal nuclear density. The kaons (K+,K0), produced inside the nucleus, are characterized by arelatively large mean free path (λ ≈ 5 fm for pK <900 MeV/c) and feel a repulsive potential of moderatestrength (about +30 MeV [1], cf. discussion in [2]). Thecase of antikaons (K−) is much more involved, as thesehadron species propagate in an attractive potential that hasa sizeable imaginary part, related to the in-medium absorp-tion. Existing data on the in-medium effects in the antikaonproduction at nuclear targets are very scarce [3].In summer 2014 the HADES collaboration successfullyperformed a pilot pion beam run (p = 1.7 GeV/c) employ-ing carbon and tungsten targets. For each target more than100 million of events were collected. Charged kaons canbe reconstructed by means of time-of-flight and momen-tum measurements combined in the mass observable. For12C and 184W targets, separately, about 100 × 103 K+’sand 10 × 103 K−’s were reconstructed (Fig. 1). The richstatistics of the charged kaon sample allows to perform atwo-dimensional analysis of the kaon phase space.]2M [MeV/c300 400 500 600 700050001000015000Figure 1: K+ signal in the mass spectrum of positivelycharged particles (piC run). The dashed vertical line showsthe nominal charged kaon mass. A fit with a gaus (sig-nal) plus a 5th order Chebyshev polynomial (background)is shown.Figure 2 shows raw doubly-differential (transverse mo-mentum vs. rapidity) yields of K+’s reconstructed in thepion-carbon run. Thanks to the high statistics of the datasample and the large acceptance of the HADES setup, a∗Work supported by BMBF 05P12WOGHH† kirill.lapidus@ph.tum.demajor part of the kaon phase space can be accessed. Thiswill allow, after the application of necessary efficiency cor-rections, to extrapolate the kaon yield to the full solid angleand extract the production cross section. The FOPI collab-oration has demonstrated [1], that for the pion beam thetotal K0 production cross section scales with the surface ofthe target nucleus (σK0tot ∝ A2/3, where A is the mass num-ber). An analogous behaviour is expected for K+’s. Thenew HADES data allows to extract the A-dependence ofthe production cross section for antikaons as well, whichtill now has not been done for pion-induced reactions. Adeviation of the exponent from the value of 2/3 would indi-cate: a) an increased absorption of the antikaons (a smallervalue of the exponent) or b) a decreased threshold for theantikaon production due to the attractive potential (rise ofthe exponent).2.3e+03 3.9e+03 5.0e+03 6.4e+03 6.0e+03 5.2e+034.0e+03 6.9e+03 7.7e+03 7.6e+03 7.2e+03 7.1e+032.9e+03 5.6e+03 6.9e+03 7.6e+03 8.1e+03 6.0e+031.9e+03 3.0e+03 3.9e+03 4.4e+03 4.5e+03 2.8e+03y0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 [MeV/c]tp1502002503003504004505005502000300040005000600070008000Figure 2: Raw K+ yields extracted in pion-carbon run. Noefficiency corrections have been applied.References[1] M. L. Benabderrahmane et al. [FOPI Collaboration], “Mea-surement of the in-medium K0 inclusive cross section inpi−-induced reactions at 1.15 GeV/c,” Phys. Rev. Lett. 102,182501 (2009).[2] G. Agakishiev et al. [HADES Collaboration], “Medium ef-fects in proton-induced K0 production at 3.5 GeV,” Phys.Rev. C 90, 054906 (2014).[3] W. Scheinast et al. [KaoS Collaboration], “First observa-tion of in-medium effects on phase space distributions of an-tikaons measured in proton-nucleus collisions,” Phys. Rev.Lett. 96 072301 (2006).MU-NQM-HADES-23 GSI SCIENTIFIC REPORT 201426 DOI:10.15120/GR-2015-1-MU-NQM-HADES-23

Charged kaon production in pion-nucleus reactions at 1.7 GeV/c

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Charged kaon production in pion-nucleus reactions at 1.7 GeV/c

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