Abstract
We use QCD sum rules to test the nature of the recently observed mesons Y ( 4260 ) , Y ( 4350 ) and Y ( 4660 ) , assumed to be exotic four-quark ( c c ¯ q q ¯ ) or ( c c ¯ s s ¯ ) states with J PC = 1 − − . We work at leading order in α s , consider the contributions of higher dimension condensates and keep terms which are linear in the strange quark mass m s . We find for the ( c c ¯ s s ¯ ) state a mass m Y = ( 4.65 ± 0.10 ) GeV which is compatible with the experimental candidate Y ( 4660 ) , while for the ( c c ¯ q q ¯ ) state we find a mass m Y = ( 4.49 ± 0.11 ) GeV , which is still consistent with the mass of the experimental candidate Y ( 4350 ) . With the tetraquark structure we are working we cannot explain the Y ( 4260 ) as a tetraquark state. We also consider molecular D s 0 D ¯ s ∗ and D 0 D ¯ ∗ states. For the D s 0 D ¯ s ∗ molecular state we get m D s 0 D ¯ s ∗ = ( 4.42 ± 0.10 ) GeV which is consistent, considering the errors, with the mass of the meson Y ( 4350 ) and for the D 0 D ¯ ∗ molecular state we get m D 0 D ¯ ∗ = ( 4.27 ± 0.10 ) GeV in excellent agreement with the mass of the meson Y ( 4260 ) .
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