Elliptic anisotropy measurement of the f0(980) hadron in proton-lead collisions and evidence for its quark-antiquark composition
Journal Article
Overview
abstract
Abstract; Despite the f0(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 f0(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 f0(980) state is reconstructed via its dominant decay channel f0(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 f0(980) state, made possible by using a novel approach, and paves the way for similar studies of other exotic hadron candidates.
