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Register a new userExotic Quark Structure of Lambda(1405) in QCD Sum Rule
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A new analysis is performed in QCD sum rule for the lightest negative parity baryon Lambda (1405). Mixings of three-quark and five-quark Fock components are taken into account. Terms containing up to dimension 12 condensates are computed in the operator product expansion. It is found that the sum rule gives much stronger coupling of Lambda* to the five-quark operator so that the five-quark components occupy about 90% of Lambda (1405).
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Five-quark (5Q) picture of Lambda(1405) is studied using quenched lattice QCD with an exotic 5Q operator of Nbar{K} type. To discreminate mere Nbar{K} and Sigmapi scattering states, Hybrid Boundary Condition (HBC), a flavor-dependent boundary condition, is imposed on the quark fields along spatial direction. 5Q mass m_{5Q}simeq 1.89 GeV is obtained after the chiral extrapolation to the physical quark mass region, which is too heavy to be identified with Lambda(1405). Then, Lambda(1405) seems neither a pure 3Q state nor a pure 5Q state, and therefore we present an interesting possibility that Lambda(1405) is a mixed state of 3Q and 5Q states.
Using the QCD sum rules we test if the charmonium-like structure Y(4260), observed in the $J/psipipi$ invariant mass spectrum, can be described with a $J/psi f_0(980)$ molecular current with $J^{PC}=1^{--}$. We consider the contributions of condensates up to dimension six and we work at leading order in $alpha_s$. We keep terms which are linear in the strange quark mass $m_s$. The mass obtained for such state is $m_{Y}=(4.67pm 0.09)$ GeV, when the vector and scalar mesons are in color singlet configurations. We conclude that the proposed current can better describe the Y(4660) state that could be interpreted as a $Psi(2S) f_0(980)$ molecular state. We also use different $J^{PC}=1^{--}$ currents to study the recently observed $Y_b(10890)$ state. Our findings indicate that the $Y_b(10890)$ can be well described by a scalar-vector tetraquark current.
We use the QCD sum rules to evaluate the mass of a possible scalar mesonic state that couples to a molecular $D_{s}^{*}bar{D}_s^{*}$ current. We find a mass $m_{D_s^*D_s^*}=(4.14pm 0.09)$ GeV, which is in a excellent agreement with the recently observed Y(4140) charmonium state. We consider the contributions of condensates up to dimension eight, we work at leading order in $alpha_s$ and we keep terms which are linear in the strange quark mass $m_s$. We also consider a molecular $D^{*}bar{D}^{*}$ current and we obtain $m_{D^*{D}^*}=(4.13pm 0.10)$, around 200 MeV above the mass of the Y(3930) charmonium state. We conclude that it is possible to describe the Y(4140) structure as a $D_s^*bar{D}_s^*$ molecular state.
We calculate the isoscalar axial-vector coupling constants of the Lambda hyperon using the method of QCD sum rules. A determination of these coupling constants reveals the individual contributions of the u, d and the s quarks to the spin content of Lambda. Our results for the light-quark contributions are in agreement with those from experiment assuming flavor SU(3). We also find that the flavor-SU(3)-breaking effects are small and the contributions from the u and the d quarks to the Lambda polarization are negatively polarized as in the flavor-SU(3) limit.
We derive a new QCD sum rule for $D(0^+)$ which has only the $Dpi$ continuum with a resonance in the hadron side, using the assumption similar to that has been successfully used in our previous work to the mass of $D_s(0^+)(2317)$. For the value of the pole mass $M_c=1.38 $ GeV as used in the $D_s(0^+)$ case we find that the mass of $D(0^+)$ derived from this sum rule is significantly lower than that derived from the sum rule with the pole approximation. Our result is in agreement with the experimental dada from Belle.
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