a1(1420)resonance as a tetraquark state and its isospin partner

Abstract

We systematically construct tetraquark currents of I G J P C = 1 − 1 ++ and classify them into types A (antisymmetric), S (symmetric) and M (mixed), based on flavor symmetries of diquarks and antidiquarks composing the tetra quark currents. We use tetraquark currents of type M to perform QCD sum rule analyses, and find a tetraquark current η M 5µ with quark contents qsqs (q = u or d) leading to a mass of 1.44 ± 0.08 GeV consistent with the a1(1420) state recently observed by the COMPASS collaboration. Our results support tetraquark explanations for both a1(1420) and f1(1420), assuming that they are isospin partners. We also study their possible decay patterns. As tetraquark candidates, the possible decay modes of a1(1420) are S-wave a1(1420) → K * (892)K and P -wave a1(1420) → f0(980)π while the possible decay patterns of f1(1420) are S-wave f1(1420) → K * (892)K and P -wave f1(1420) → a0(980)π. We speculate that a1(1420) is partly responsible for the large isospin violation in the η(1405) → f0(980)π0 decay mode which is reported by BESIII collaboration in the J/ψ → γ3π process.

New a1(1420) state: Structure, mass, and width

“…It is also in accord within small computational errors with the prediction obtained in Ref. [22]. The full width of the a 1 ð1420Þ meson has been calculated on basis of its five decay channels and led to Γ ¼ ð145.52 AE 20.79Þ MeV.…”

“…The a 1 ð1420Þ meson as a pure diquark-antidiquark state was explored in Ref. [22], results of which are in accord with data, as well. It is worth noting that in both of these works QCD two-point sum rule method were used.…”

“…[22]: there is a large overlap region between two predictions. It is worth noting that we have rescaled the couplingf a 1 ≡ f a 1 m a 1 ¼ ð1.9 AE 0.5Þ × 10 −3 GeV 5 in accordance with our definition Eq.…”

“…In the chiral limit adopted in present paper the particles a 1 ð1420Þ and f 1 ð1420Þ have equal masses (see, Ref. [22]). …”

“…In the present work for the a 1 ð1420Þ meson we choose an interpolating current that belongs to a class of currents with the mixed-type flavor symmetry (detailed discussion of these questions was presented in Ref. [22])…”