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Register a new userQCD sum rules study of $QQ-bar{u}bar{d}$ mesons
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We use QCD sum rules to study the possible existence of $QQ-bar{u}bar{d}$ mesons, assumed to be a state with $J^{P}=1^{+}$. For definiteness, we work with a current with an axial heavy diquark and a scalar light antidiquark, at leading order in $alpha_s$. We consider the contributions of condensates up to dimension eight. For the $b$-quark, we predict $M_{T_{bb}}= (10.2pm 0.3) {rm GeV}$, which is below the $bar{B}bar{B}^*$ threshold. For the $c$-quark, we predict $M_{T_{cc}}= (4.0pm 0.2) {rm GeV}$, in agreement with quark model predictions.
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Very recently, the LHCb Collaboration observed distinct structures with the $ccbar{c}bar{c}$ in the $J/Psi$-pair mass spectrum. In this work, we construct four scalar ($J^{PC} = 0^{++}$) $[8_c]_{Qbar{Q^prime}}otimes [8_c]_{Q^prime bar{Q}}$ type currents to investigate the fully-heavy tetraquark state $Q Q^prime bar{Q} bar{Q^prime}$ in the framework of QCD sum rules, where $Q=c, b$ and $Q^prime = c, b$. Our results suggest that the broad structure around 6.2-6.8 GeV can be interpreted as the $0^{++}$ octet-octet tetraquark states with masses $6.44pm 0.11$ GeV and $6.52pm 0.10$ GeV, and the narrow structure around $6.9$ GeV can be interpreted as the $0^{++}$ octet-octet tetraquark states with masses $6.87pm 0.11$ GeV and $6.96pm 0.11$ GeV, respectivley. Extending to the b-quark sector,the masses of their fully-bottom partners are found to be around 18.38-18.59 GeV. Additionally, we also analyze the spectra of the $[cbar{c}][bbar{b}]$ and $[cbar{b}] [b bar{c}]$ tetraquark states, which lie in the range of 12.51-12.74 GeV and 12.49-12.81 GeV, respectively.
In this article, we assume that there exist the pseudoscalar $Dbar{D}_{s0}^*(2317)$ and $D^*bar{D}_{s1}^*(2460)$ molecular states $Z_{1,2}$ and construct the color singlet-singlet molecule-type interpolating currents to study their masses with the QCD sum rules. In calculations, we consider the contributions of the vacuum condensates up to dimension-10 and use the formula $mu=sqrt{M_{X/Y/Z}^{2}-left(2{mathbb{M}}_{c}right)^{2}}$ to determine the energy scales of the QCD spectral densities. The numerical results, $M_{Z_1}=4.61_{-0.08}^{+0.11},text{GeV}$ and $M_{Z_2}=4.60_{-0.06}^{+0.07},text{GeV}$, which lie above the $Dbar{D}_{s0}^*(2317)$ and $D^*bar{D}_{s1}^*(2460)$ thresholds respectively, indicate that the $Dbar{D}_{s0}^*(2317)$ and $D^*bar{D}_{s1}^*(2460)$ are difficult to form bound state molecular states, the $Z_{1,2}$ are probably resonance states.
In this article, we construct the six-quark currents with the $J^P=0^+$, $0^-$, $1^+$ and $1^-$ to study the $Lambda_c$$Lambda_c$ dibaryon and $Lambda_c$$bar{Lambda}_c$ baryonium states via QCD sum rules. We consider the vacuum condensates up to dimension 16 and truncation of the order $mathcal{O}(alpha_s^k )$ with $kleq3$. The predicted masses are $5.11_{-0.12}^{+0.15}$GeV, $4.66_{-0.06}^{+0.10}$GeV, $4.99_{-0.09}^{+0.10}$GeV $4.68^{+0.08}_{-0.08}$GeV for the $J^P=0^+$, $0^-$, $1^+$ and $1^-$ states, respectively, which can be confronted to the experimental data in the future considering the high integrated luminosity at the center-of-mass energy about $4.8,rm{GeV}$ at the BESIII. We find the terms with $frac{3}{2}< k leq 3$ do play a tiny role, and we can ignore these terms safely in the QCD sum rules.
The mass and coupling of the scalar tetraquark $T_{bb;overline{u}overline{d }}^{-}$ (hereafter $T_{b:overline{d}}^{-} $) are calculated in the context of the QCD two-point sum rule method. In computations we take into account effects of various quark, gluon and mixed condensates up to dimension ten. The result obtained for the mass of this state $m=(10135pm 240)~mathrm{MeV} $ demonstrates that it is stable against the strong and electromagnetic decays. We also explore the dominant semileptonic $T_{b:overline{d}}^{-} to widetilde{Z}_{bc;bar{u}bar{d}}^{0}loverline{ u }_{l}$ and nonleptonic decays $T_{b:overline{d}}^{-} to widetilde{Z}_{bc;bar{u}bar{ d}}^{0}M$, where $widetilde{Z}_{bc;bar{u}bar{d}}^{0}$ is the scalar tetraquark composed of color-sextet diquark and antidiquark, and $M$ is one of the final-state pseudoscalar mesons $pi^{-}, K^{-}, D^{-}$ and $D_s^{-}$ , respectively. The partial widths of these processes are calculated in terms of the weak form factors $G_{1(2)}(q^2)$, which are determined from the QCD three-point sum rules. Predictions for the mass, full width $Gamma _{mathrm{full}} =(10.88pm 1.88)times 10^{-10}~mathrm{MeV}$, and mean lifetime $tau=0.61_{-0.09}^{+0.13}~mathrm{ps}$ of the $T_{b:overline{d} }^{-}$ obtained in the present work can be used in theoretical and experimental studies of this exotic state.
We evaluate long-distance electromagnetic (QED) contributions to $bar{B}{}^0 to D^+ tau^{-} bar{ u}_{tau}$ and $B^- to D^0 tau^{-} bar{ u}_{tau}$ relative to $bar{B}{}^0 to D^+ mu^{-} bar{ u}_{mu}$ and $B^- to D^0 mu^{-} bar{ u}_{mu}$, respectively, in the standard model. We point out that the QED corrections to the ratios $R(D^{+})$ and $R(D^{0})$ are not negligible, contrary to the expectation that radiative corrections are almost canceled out in the ratio of the two branching fractions. The reason is that long-distance QED corrections depend on the masses and relative velocities of the daughter particles. We find that theoretical predictions for $R(D^{+})^{tau/mu}$ and $R(D^{0})^{tau/mu}$ can be amplified by $sim4%$ and $sim3%$, respectively, for the soft-photon energy cut in range $20$-$40$ MeV.
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