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 (qq) meson, a tetraquark (qqqq) exotic state, a kaon-antikaon
(KK) molecule, or a quark-antiquark-gluon (qqg) hybrid. This paper reports
strong evidence that the f0(980) state is an ordinary qq meson, inferred from
the scaling of elliptic anisotropies (v2) with the number of constituent quarks
(nq), 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 v2 is measured as a function of transverse
momentum (pT). It is found that the nq = 2 (qq state) hypothesis is favored over
nq = 4 (qqqq or KK states) by 7.7, 6.3, or 3.1 standard deviations in the pT < 10, 8,
or 6 GeV/c ranges, respectively, and over nq = 3 (qqg hybrid state) by
3.5 standard deviations in the pT < 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
