Antitriplet States Research Articles

Excited doubly heavy baryon production via W+ boson decays

In this paper, decay widths of the doubly heavy baryons (${\mathrm{\ensuremath{\Xi}}}_{cc}$ and ${\mathrm{\ensuremath{\Xi}}}_{bc}$) production are theoretically calculated in the whole phase space through ${W}^{+}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{cc}+\overline{c}+\overline{s}$ and ${W}^{+}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Xi}}}_{bc}+\overline{b}+\overline{s}$, within the framework of nonrelativistic QCD (NRQCD). Differential widths $d\mathrm{\ensuremath{\Gamma}}/d{s}_{12}$, $d\mathrm{\ensuremath{\Gamma}}/d{s}_{23}$, $d\mathrm{\ensuremath{\Gamma}}/d\mathrm{cos}{\ensuremath{\theta}}_{12}$, and $d\mathrm{\ensuremath{\Gamma}}/d\mathrm{cos}{\ensuremath{\theta}}_{13}$ are also given. In addition to the ordinary S-wave contributions for the baryons, we specifically calculate P-wave contributions as a comparison, namely the high excited states of the intermediate diquark, including $[{^{1}P}_{1}]$ and $[{^{1}P}_{J}]$ (with $J=0,1,2$) in both color antitriplet state $\overline{\mathbf{3}}$ and color sextuplet state $\mathbf{6}$. It shows that the contribution from the P-wave is about one order lower than the S-wave. According to the results, we can expect plentiful events produced at the LHC, i.e., $3.69\ifmmode\times\else\texttimes\fi{}{10}^{5}\text{ }\text{ }{\mathrm{\ensuremath{\Xi}}}_{cc}$ events and $4.91\ifmmode\times\else\texttimes\fi{}{10}^{4}\text{ }\text{ }{\mathrm{\ensuremath{\Xi}}}_{bc}$ events per year.

Magnetic moments of the spin−1/2 singly charmed baryons in covariant baryon chiral perturbation theory

Recent experimental advances have reignited theoretical interests in heavy-flavor hadrons. In this work, we study the magnetic moments of the spin-1/2 singly charmed baryons up to the next-to-leading order in covariant baryon chiral perturbation theory with the extended-on-mass-shell renormalization scheme. The pertinent low energy constants $g_{1-4}$ are fixed with the help of the quark model and the heavy quark spin flavor symmetry, while the remaining $d_2$, $d_3$, $d_5$ and $d_6$ are determined by fitting to the lattice QCD pion-mass dependent data. We study the magnetic moments as a function of $m_\pi^2$ and compare our results with those obtained in the heavy baryon chiral perturbation theory. We find that the loop corrections induced by the anti-triplet states are dominated by the baryon pole diagram. In addition, we predict the magnetic moments of the spin-1/2 singly charmed baryons and compare them with those of other approaches.

On heavy–light meson resonances and chiral symmetry

We study heavy–light meson resonances with quantum numbers JP=0+ and JP=1+ in terms of the non-linear chiral SU(3) Lagrangian. At leading order a parameter-free prediction is obtained for the scattering of Goldstone bosons off heavy–light pseudo-scalar and vector mesons. The recently announced narrow open-charm states observed by the BABAR and CLEO Collaborations are reproduced. We suggest the existence of states that form an anti-triplet and a sextet representation of the SU(3) group. In particular, so far unobserved narrow isospin-singlet states with negative strangeness are predicted. The open-beauty states with (I,S)=(0,−1) are anticipated at 5761 MeV (JP=0+) and 5807 MeV (JP=1+). For the anti-triplet states our results differ most significantly from predictions that are based on the chiral quark model in the open-beauty sector. Strongly bound 0+- and 1+-states with (I,S)=(0,1) at 5643 and 5690 MeV are predicted.

Constituent quarks, diquarks and the N − Δ mass splitting

We analyze hadron as well as quark and diquark correlation functions in Landau gauge in order to extract information on the spin dependence of the quark-quark interaction. We find evidence that the N − Δ mass splitting can be attributed to the spin dependence of the interaction between quarks in a colour anti-triplet state with spin 0 and 1, respectively. The lightest excitations are observed in the S = 0 channel. However, no evidence for a deeply bound diquark state is found.

Diquark masses from lattice QCD

We present first results for diquark masses calculated in Landau gauge on the lattice. These masses as well as quark and baryon masses have been extracted from the long distance behavior of the correlation functions. We find that the ordering of the diquark spectrum with spin 0 and 1 states in color anti-triplet and sextet channels is in accordance with instanton motivated interaction models. We observe an attractive interaction for color anti-triplet states with a splitting between spin 0 and spin 1 diquarks that can account for the mass splitting between the nucleon and the delta. Our calculation provides no evidence for a deeply bound diquark state.

Diquark masses from lattice QCD

We present first results for diquark correlation functions calculated in Landau gauge on the lattice. Masses have been extracted from the long distance behaviour of these correlation functions. We find that the ordering of diquark masses with spin 0 and 1 states in colour anti-triplet and sextet channels is in accordance with instanton motivated interaction models. Although we find evidence for an attractive interaction in colour anti-triplet states with a splitting between spin 0 and spin 1 diquarks that can account for the mass splitting between the nucleon and the delta, there is no evidence for a deeply bound diquark state.

THE RESOLUTION OF THE |ΔI|=1/2 PUZZLE

Progress in the understanding of non-leptonic weak decays with its intricate interplay of weak and strong interactions is reported. At low energies the dynamics of these processes is strongly influenced by non-perturbative correlations between two quarks in Lorentz scalar color antitriplet states. A coherent description of kaon and hyperon decays emerges resolving so far mysterious puzzles.

Hyperon decays and quark-quark correlations

The nonleptonic weak Hamiltonian strongly favours the annihilation and creation of correlated quark pairs in spin zero and colour antitriplet states. It is demonstrated that bothS- andP-wave nonleptonic hyperon decays are well described by this mechanism if supplemented by factorization contributions. Apart from the use of mass values and the π-nucleon coupling constant, the results are obtained in a parameter free way. Since the diquark properties applied are identical to the ones used in the calculation ofK→2π decays and the long range contribution to theKL−KS mass difference, a coherent physical picture of dominant nonperturbative effects in the low energy domain is reached.

The resolution of the [formula omitted] puzzle

Progress in the understanding of nonleptonic weak decays is reported. Nonperturbative long-range QCD forces between two quarks in colour antitriplet states lead to quasi particles, diquarks. It is shown that the creation and annihilation of these diquarks by the weak Hamiltonian is a dominant process which allows the successful calculation of hyperon and K-decay amplitudes and thus explains the |Δ I| = 1 2 enhancement observed in these decays.

Nonleptonic weak decays, flavour oscillations, and diquarks

Recent improvements in the theoretical understanding of nonleptonic weak decays of strange particles are presented. The dynamics of these processes in strongly influenced by nonperturbative correlations between two quarks in a scalar colour antitriplet state. A coherent description of the δl= 1 2 rule in kaon and hyperon decays as well as the K L −K S mass difference emerges. Some connections between the ideas presented here and different approaches are pointed out.