Elliptic anisotropy measurement of the f0(980) hadron in proton-lead collisions and evidence for its quark-antiquark composition
- A. Hayrapetyan
- A. Tumasyan
- W. Adam
- J. W. Andrejkovic
- T. Bergauer
- S. Chatterjee
- K. Damanakis
- M. Dragicevic
- P. S. Hussain
- M. Jeitler
- N. Krammer
- A. Li
- D. Liko
- I. Mikulec
- J. Schieck
- R. Schöfbeck
- D. Schwarz
- M. Sonawane
- S. Templ
- W. Waltenberger
- C.-E. Wulz
- M. R. Darwish
- T. Janssen
- P. Van Mechelen
- E. S. Bols
- J. D’Hondt
- S. Dansana
- A. De Moor
- M. Delcourt
- H. El Faham
- S. Lowette
- I. Makarenko
- D. Müller
- S. Tavernier
- M. Tytgat
- G. P. Van Onsem
- S. Van Putte
- D. Vannerom
- B. Clerbaux
- A. K. Das
- G. De Lentdecker
- H. Evard
- L. Favart
- P. Gianneios
- D. Hohov
- J. Jaramillo
- A. Khalilzadeh
- F. A. Khan
- K. Lee
- M. Mahdavikhorrami
2025-08-27
Despite the f 0 (980) hadron having been discovered half a century ago, the question about its quark content has not been settled: it might be an ordinary quark-antiquark ( $${{\rm{q}}}\overline{{{\rm{q}}}}$$ q q ¯ ) meson, a tetraquark ( $${{\rm{q}}}\overline{{{\rm{q}}}}{{\rm{q}}}\overline{{{\rm{q}}}}$$ q q ¯ q q ¯ ) exotic state, a kaon-antikaon ( $${{\rm{K}}}\overline{{{\rm{K}}}}$$ K K ¯ ) molecule, or a quark-antiquark-gluon ( $${{\rm{q}}}\overline{{{\rm{q}}}}{{\rm{g}}}$$ q q ¯ g ) hybrid. This paper reports strong evidence that the f 0 (980) state is an ordinary $${{\rm{q}}}\overline{{{\rm{q}}}}$$ q q ¯ meson, inferred from the scaling of elliptic anisotropies ( v 2 ) with the number of constituent quarks ( n q ), as empirically established using conventional hadrons in relativistic heavy ion collisions. The f 0 (980) state is reconstructed via its dominant decay channel f 0 (980) → π + π − , in proton-lead collisions recorded by the CMS experiment at the LHC, and its v 2 is measured as a function of transverse momentum ( p T ). It is found that the n q = 2 ( $${{\rm{q}}}\overline{{{\rm{q}}}}$$ q q ¯ state) hypothesis is favored over n q = 4 ( $${{\rm{q}}}\overline{{{\rm{q}}}}{{\rm{q}}}\overline{{{\rm{q}}}}$$ q q ¯ q q ¯ or $${{\rm{K}}}\overline{{{\rm{K}}}}$$ K K ¯ states) by 7.7, 6.3, or 3.1 standard deviations in the p T < 10, 8, or 6 GeV/ c ranges, respectively, and over n q = 3 ( $${{\rm{q}}}\overline{{{\rm{q}}}}{{\rm{g}}}$$ q q ¯ g hybrid state) by 3.5 standard deviations in the p T < 8 GeV/ c range. This result represents the first determination of the quark content of the f 0 (980) state, made possible by using a novel approach, and paves the way for similar studies of other exotic hadron candidates.