Evidence of isospin-symmetry violation in high-energy collisions of atomic nuclei

(NA61/SHINE) Adhikary, H.; Adrich, P.; Allison, K. K.; Amin, N.; Andronov, E. V.; Arsene, I. -C.; Bajda, M.; Balkova, Y.; Battaglia, D.; Bazgir, A.; Bhosale, S.; Bielewicz, M.; Blondel, A.; Bogomilov, M.; Bondar, Y.; Brandin, A.; Bryliński, W.; Brzychczyk, J.; Buryakov, M.; Camino, A. F.; Ćirković, M.; Csanád, M.; Cybowska, J.; Czopowicz, T.; Dalmazzone, C.; Davis, N.; Dmitriev, A.; von Doetinchem, P.; Dominik, W.; Dumarchez, J.; Engel, R.; Feofilov, G. A.; Fields, L.; Fodor, Z.; Friend, M.; Gaździcki, M.; Golosov, O.; Golovatyuk, V.; Golubeva, M.; Grebieszkow, K.; Guber, F.; Igolkin, S. N.; Ilieva, S.; Ivashkin, A.; Izvestnyy, A.; Kargin, N.; Karpushkin, N.; Kashirin, E.; Kiełbowicz, M.; Kireyeu, V. A.; Kolesnikov, R.; Kolev, D.; Koshio, Y.; Kovalenko, V. N.; Kowalski, S.; Kozłowski, B.; Krasnoperov, A.; Kucewicz, W.; Kuchowicz, M.; Kuich, M.; Kurepin, A.; László, A.; Lewicki, M.; Lykasov, G.; Lyubushkin, V. V.; Maćkowiak-Pawłowska, M.; Majka, Z.; Makhnev, A.; Maksiak, B.; Malakhov, A. I.; Marcinek, A.; Marino, A. D.; Mathes, H. -J.; Matulewicz, T.; Matveev, V.; Melkumov, G. L.; Merzlaya, A.; Mik, Ł.; Morozov, S.; Nagai, Y.; Nakadaira, T.; Naskret, M.; Nishimori, S.; Olivier, A.; Ozvenchuk, V.; Panova, O.; Paolone, V.; Petukhov, O.; Pidhurskyi, I.; Płaneta, R.; Podlaski, P.; Popov, B. A.; Pórfy, B.; Prokhorova, D. S.; Pszczel, D.; Puławski, S.; Puzović, J.; Renfordt, R.; 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.; Rybka, D.; Sakashita, K.; Schmidt, K.; Seryakov, A. Y.; Seyboth, P.; Shah, U. A.; Shiraishi, Y.; Shukla, A.; Słodkowski, M.; Staszel, P.; Stefanek, G.; Stepaniak, J.; Strikhanov, M.; Ströbele, H.; Šuša, Tatjana; Świderski, Ł.; Szewiński, J.; Szukiewicz, R.; Taranenko, A.; Tefelska, A.; Tefelski, D.; Tereshchenko, V.; Tsenov, R.; Turko, L.; Tveter, T. S.; Unger, M.; Urbaniak, M.; Valiev, F. F.; Veberič, D.; Vechernin, V. V.; Vitiuk, O.; Volkov, V.; Wickremasinghe, A.; Witek, K.; Wójcik, K.; Wyszyński, O.; Zaitsev, A.; Zherebtsova, E.; Zimmerman, E. D.; Zviagina, A.; Zwaska, R.; Giacosa, F.; Gorenstein, M.; Poberezhniuk, R.; Samanta, S. (2025) Evidence of isospin-symmetry violation in high-energy collisions of atomic nuclei. Nature Communications, 16 (1). ISSN 2041-1723

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Abstract

Strong interactions preserve an approximate isospin symmetry between up (u) and down (d) quarks, part of the more general flavor symmetry. In the case of K meson production, if this isospin symmetry were exact, it would result in equal numbers of charged (K+ and K-) and neutral (K-0 and K(0)) mesons produced in collisions of isospin-symmetric atomic nuclei. Here, we report results on the relative abundance of charged over neutral K meson production in argon and scandium nuclei collisions at a center-of-mass energy of 11.9 GeV per nucleon pair. We find that the production of K+ and K- mesons at mid-rapidity is (18.4 +/- 6.1)% higher than that of the neutral K mesons. Although with large uncertainties, earlier data on nucleus-nucleus collisions in the collision center-of-mass energy range 2.6 < root s(NN )< 200 GeV are consistent with the present result. Using well-established models for hadron production, we demonstrate that known isospin-symmetry breaking effects and the initial nuclei containing more neutrons than protons lead only to a small (few percent) deviation of the charged-to-neutral kaon ratio from unity at high energies. Thus, they cannot explain the measurements. The significance of the flavor-symmetry violation beyond the known effects is 4.7 sigma when the compilation of world data with uncertainties quoted by the experiments is used. New systematic, high-precision measurements and theoretical efforts are needed to establish the origin of the observed large isospin-symmetry breaking.

Item Type:	Article
Uncontrolled Keywords:	CERN; SPS; NA61/SHINE; charged-to-neutral kaon ratio
Subjects:	NATURAL SCIENCES > Physics
Divisions:	Division of Experimental Physics
Depositing User:	Ema Buhin Šaler
Date Deposited:	05 Mar 2026 12:44
URI:	http://fulir.irb.hr/id/eprint/11324
DOI:	10.1038/s41467-025-57234-6

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