Search

We indicated in our previous work that for QED the role of the scalar potential which appears at the loop level is much smaller than that of the vector potential and is in fact negligible. But the situation is different for QCD, one reason is that the loop effects are more significant because αs is much larger than α, and second the non-perturbative QCD effects may induce a sizable scalar potential. In this work, we study phenomenologically the contribution of the scalar potential to the spectra of charmonia, bottomonia and b(c) families. Taking into account both vector and scalar potentials, by fitting the well measured charmonia and bottomonia spectra, we re-fix the relevant parameters and test them by calculating other states of not only the charmonia and bottomonia families, but also the b family. We also consider the Lamb shift of the spectra.

It is interesting to determine the fraction of the gluonium component in η and η′ which has been under serious discussion for many years. Measurements on different decay and/or production modes were employed in literatures, thus larger uncertainties were unavoidable. In this paper we suggest to determine the mixing angles of η-η′-G using the data of semileptonic decays of D and Ds. We extract the mixing angles ϕ′, ϕG and the model parameters simultaneously. Thanks to the new measurements carried out by CLEO Collaboration and there are sufficient decay modes to determine both the model parameters and mixing angles. The mixing angles from data are ϕ′ = (41.5 ± 2.0)° and sin ϕG = 0.00 ± 0.36. Even though the central value of sin ϕG is still zero, an upper bound is set. Moreover, as suggested in literature, η(1405) is a glueball candidate whereas in our picture, η(1405) may be identified as G with glueonium being its main content. Using all the model-parameters obtained above, we estimate the branching ratios of [Formula: see text] where G is identified as η(1405).

We indicated in our previous work that for QED the contributions of the scalar potential which appears at the loop level is much smaller than that of the vector potential and in fact negligible. But the situation may be different for QCD, one reason is that the loop effects are more significant because $\alpha_s$ is much larger than $\alpha$, and secondly the non-perturbative QCD effects may induce the scalar potential. In this work, we phenomenologically study the contribution of the scalar potential to the spectra of charmonia. Taking into account both vector and scalar potentials, by fitting the well measured charmonia spectra, we re-fix the relevant parameters and test them by calculating other states of the charmonia family. We also consider the role of the Lamb shift and present the numerical results with and without involving the Lamb shift.

Contributions of fermions to the mass of the scalar glueball $0^{++}$ are calculated at two-loop level in the framework of QCD sum rules. It obviously changes the coefficients in the operator product expansion (OPE) and shifts the mass of glueball.

We calculate the forward backward asymmetry of the top-pair production at TEVATRON up to next to leading order (NLO) in the little Higgs model (LHM). We find that the contribution of $Z_H$ can be large enough to make up the gap between standard model (SM) prediction and data. With the database of $7.65\pm0.20\pm0.36$ pb, therefore, the parameter space for flavor-changing coupling of $Z_H$ is constrained. Thus this model can result in the required asymmetry while the total cross section of top-pair production remaining consistent with data., 8 figures

We present recent LHCb results in the quarkonia production with three topics. With 1 fb$^{-1}$ data collected in 2011 with pp collisions at a proton-proton center-of-mass energy $\sqrt{s}$ = 7 TeV, the ratios of $\sigma(\chi_c 0)/\sigma(\chi_c 2)$ and $\sigma(\chi_c 2)/\sigma(\chi_c 1)$ are measured. With 0.37 fb$^{-1}$ data collected in 2011, the polarization of prompt $J/\psi$ is measured using an angular analysis of the decay $J/\psi \to \mu^+\mu^-$. Finally the production of $J/\psi$ is studied with the 1.6 nb$^{-1}$ data collected in 2013 with proton-lead collisions at a proton-nucleon center-of-mass energy $\sqrt{s_{NN}}$ = 5 TeV. The nuclear modification factor and the forward-backward production ratio are determined for prompt $J/\psi$ and $J/\psi$ from b-hadron decays for the first time.

Whether molecular states indeed exist in nature has been disputed for a long time. Several new resonances have been observed in the recent experiments and they seem to be of exotic structures and some of them have been proposed to be molecular states. The very recent observation of $Z_b(10610)[(10608.4\pm 2.0)$ MeV] and $Z_b(10650)[(10653.2\pm 1.5)$ MeV] encourages the interpretation of multi-quark states. In the Beter-Salpeter (BS) approach, we study the possibility if two heavy mesons can form a molecular state by exchanging light mesons. Our results indicate that two heavy mesons can form an isospin singlet (I=0) bound state but cannot form an isospin triplet (I=1) when the contribution of $\sigma-$ exchange is reasonably small, i.e. as the coupling of $\sigma$ with mesons $g_{\sigma}$ takes the value given in previous literatures. Thus we conclude that the newly observed $Z_b(10610)$ should not be a molecular state, but a tetraquark state instead, at most, the fraction of the molecular state in the physical resonance $Z_b(10610)$ is tiny., Comment: 15 pages, 2 figures, an important reference added; Accepted by JHEP

In this work, we calculate the mass spectrum of doubly heavy baryons with the diquark model in terms of the QCD sum rules. The interpolating currents are composed of a heavy diquark field and a light quark field. Contributions of the operators up to dimension six are taken into account in the operator product expansion. Within a reasonable error tolerance, our numerical results are compatible with other theoretical predictions. This indicates that the diquark picture reflects the reality and is applicable to the study of doubly heavy baryons., Comment: 23 pages, 9 figures, minor corrections in expressions