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  • Evidence for an excess of charged over neutral $K$ meson production in high-energy collisions of atomic nuclei
    Collaboration, NA61/SHINE; :; Adhikary, H; Allison, K. K; Amin, N; Andronov, E. V; Arsene, I. -C; Bajda, M; Balkova, Y; Bogomilov, M; Bondar, Y; Brandin, A; Brylinski, W; Brzychczyk, J; Buryakov, M; Cirkovic, M; Csanád, M; Cybowska, J; Davis, N; von Doetinchem, P; Dumarchez, J; Feofilov, G. A; Fodor, Z; Friend, M; Gazdzicki, M; Guber, F; Ilieva, S; Ivashkin, A; Kargin, N; Karpushkin, N; Kashirin, E; Kireyeu, V. A; Koshio, Y; Kovalenko, V. N; Kowalski, S; Kucewicz, W; Kuchowicz, M; Kuich, M; László, A; Lewicki, M; Lykasov, G; Majka, Z; Makhnev, A; Maksiak, B; Matulewicz, T; Matveev, V; Melkumov, G. L; Merzlaya, A; Mik, Ł; Nagai, Y; Nakadaira, T; Nishimori, S; Paolone, V; Pidhurskyi, I; Płaneta, R; Popov, B. A; Prokhorova, D. S; Pszczel, D; Puławski, S; Puzovic, J; Ren, L; Ortiz, V. Z. Reyna; Röhrich, D; Rondio, E; Roth, M; Rozpłochowski, Ł; Rumberger, B. T; Rumyantsev, M; Rustamov, A; Rybczynski, M; Rybicki, A; Sakashita, K; Schmidt, K; Seryakov, A. Yu; Seyboth, P; Shah, U. A; Słodkowski, M; Stepaniak, J; Strikhanov, M; Ströbele, H; Šuša, T; Swiderski, Ł; Szukiewicz, R; Taranenko, A; Tefelska, A; Tefelski, D; Tereshchenko, V; Tsenov, R; Turko, L; Tveter, T. S; Unger, M; Valiev, F. F; Veberic, D; Vechernin, V. V; Volkov, V; Witek, K; Wójcik, K; Zaitsev, A; Zviagina, A; Zwaska, R

    12/2023
    Journal Article

    Collisions of atomic nuclei at relativistic velocities produce new particles, predominantly mesons containing one valence quark and one valence anti-quark. These particles are produced in strong interactions, which preserve an approximate symmetry between up ($u$) and down ($d$) quarks. In the case of $K$ meson production, if this symmetry were exact, it would result in equal numbers of charged ($K^+$ and $K^-$) and neutral ($K^0$ and $\overline K^0$) mesons in the final state. In this Letter, we report a measurement of the relative abundance of charged over neutral $K$ meson production in collisions of argon and scandium nuclei at a center-of-mass energy of 11.9 GeV per nucleon pair. We find that production of $\mathit{K^+}$ and $\mathit{K^-}$ mesons at mid-rapidity is $(18.4\pm 6.1)\%$ higher than that of the neutral $K$ mesons. The origin of this unexpected excess remains to be elucidated.

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