a1(1420)resonance as a tetraquark state and its isospin partner
Physical Review D
We systematically construct tetraquark currents of I^GJ^PC=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 q sq̅s̅(q=u or d) leading to a mass of 1.44 ± 0.08 GeV consistent with the a_1(1420) state recently observed by the COMPASS
... n. Our results support tetraquark explanations for both a_1(1420) and f_1(1420), assuming that they are isospin partners. We also study their possible decay patterns. As tetraquark candidates, the possible decay modes of a_1(1420) are S-wave a_1(1420) → K^*(892)K and P-wave a_1(1420)→ f_0(980) π while the possible decay patterns of f_1(1420) are S-wave f_1(1420) → K^*(892)K and P-wave f_1(1420) → a_0(980) π. We speculate that a_1(1420) is partly responsible for the large isospin violation in the η(1405)→ f_0(980)π_0 decay mode which is reported by BESIII collaboration in the J/ψ→γ 3π process.