Elliptic anisotropy measurement of the f<sub>0</sub>(980) hadron in proton-lead collisions and evidence for its quark-antiquark composition.
basic_science · Level V
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- Record sourced from PubMed, PMID 40866333.
- Also identified by DOI 10.1038/s41467-025-56200-6 and PMC identifier 12391314.
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Abstract
Despite the f<sub>0</sub>(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 ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> </math> ) meson, a tetraquark ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> <mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> </math> ) exotic state, a kaon-antikaon ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>K</mi> <mover><mrow><mi>K</mi></mrow> <mo>¯</mo></mover> </math> ) molecule, or a quark-antiquark-gluon ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> <mi>g</mi></math> ) hybrid. This paper reports strong evidence that the f<sub>0</sub>(980) state is an ordinary <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> </math> meson, inferred from the scaling of elliptic anisotropies (v<sub>2</sub>) with the number of constituent quarks (n<sub>q</sub>), as empirically established using conventional hadrons in relativistic heavy ion collisions. The f<sub>0</sub>(980) state is reconstructed via its dominant decay channel f<sub>0</sub>(980) → π<sup>+</sup>π<sup>-</sup>, in proton-lead collisions recorded by the CMS experiment at the LHC, and its v<sub>2</sub> is measured as a function of transverse momentum (p<sub>T</sub>). It is found that the n<sub>q</sub> = 2 ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> </math> state) hypothesis is favored over n<sub>q</sub> = 4 ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> <mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> </math> or <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>K</mi> <mover><mrow><mi>K</mi></mrow> <mo>¯</mo></mover> </math> states) by 7.7, 6.3, or 3.1 standard deviations in the p<sub>T</sub> < 10, 8, or 6 GeV/c ranges, respectively, and over n<sub>q</sub> = 3 ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>q</mi> <mover><mrow><mi>q</mi></mrow> <mo>¯</mo></mover> <mi>g</mi></math> hybrid state) by 3.5 standard deviations in the p<sub>T</sub> < 8 GeV/c range. This result represents the first determination of the quark content of the f<sub>0</sub>(980) state, made possible by using a novel approach, and paves the way for similar studies of other exotic hadron candidates.