Wide acceptance measurement of K−/K+ ratio from Ni+Ni collisions at 1.91A GeV

Wide acceptance measurement of K−/K+ ratio from Ni+Ni collisions at 1.91A GeV

Piasecki, K.; Herrmann, N.; Averbeck, R.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Berger, M.; Buehler, P.; Cargnelli, M.; Čaplar, R.; Cordier, E.; Crochet, P.; Czerwiakowa, O.; Deppner, I.; Dupieux, P.; Dželalija, M.; Fabbietti, L.; Fodor, Z.; Gasik, P.; Gašparić, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kiš, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Le Fèvre, A.; Liu, J. L.; Lopez, X.; Mangiarotti, A.; Manko, V.; Marton, J.; Matulewicz, T.; Merschmeyer, M.; Münzer, R.; Pelte, D.; Petrovici, M.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczyńska, K.; Smolyankin, V.; Stoicea, G.; Suzuki, K.; Tymiński, Z.; Wagner, P.; Weber, I.; Widmann, E.; Wiśniewski, K.; Xiao, Z. G.; Xu, H. S.; Yushmanov, I.; Zhang, Y.; Zhilin, A.; Zinyuk, V.; Zmeskal, J.

Abstract

The FOPI Collaboration at GSI SIS-18 synchrotron measured the charged kaons from central and semi-central collisions of Ni+Ni at the beam energy of 1.91A GeV. We present the distribution of K−/K+ ratio on the plane of energy vs polar angle in the nucleon-nucleon centre-of-mass frame, with and without the subtraction of the contribution of φ(1020) meson decays to the K− yield. The acceptance of the current experiment is substantially wider compared to the previous measurement of the same colliding system. The K−/K+ ratio is expected to be sensitive to the in-medium modifications of basic kaon properties like mass. Recent results obtained by the HADES Collaboration at 1.23A and 1.76A GeV indicate, that no mass-shift effect is needed to explain the difference between energy slopes of charged kaon spectra within uncertainties. The K−/K+ ratios obtained in this experiment, even after correction for the contribution due to the φ(1020) meson decays, decrease with increasing kinetic energy, as generally predicted in models assuming mass modifications.

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