Heavy Diquark Research Articles

Spectra of the lightest baryons containing two heavy quarks in a potential model

The spectra of baryons which include two heavy quarks can be treated as a two-body system, where the two heavy quarks constitute a bosonic diquark. We derive the effective potential between the light quark and the heavy diquark in terms of the Bethe-Salpeter equation. To obtain the spectra, several serious problems need to be solved: (1) the operator ordering, (2) the errors caused by the nonrelativistic expansion, (3) spin-spin coupling, and (4) the mixing between the scalar-diquark-baryon and vector-diquark-baryon. In this work we take reasonable approaches to deal with them.

Spectroscopy of doubly heavy baryons

Spectra of masses are calculated for the families of doubly heavy baryons in the framework of the nonrelativistic quark model with the QCD potential of Buchm\"uller and Tye. We suppose the quark-diquark structure for the wave functions and take into account the spin-dependent splittings. The physical reasons causing the existence of quasistable excited states in the subsystem of heavy diquark are considered for the heavy quarks of identical flavors.

Doubly heavy baryons in sum rules of NRQCD

The masses of baryons containing two heavy quarks and their couplings to the corresponding quark currents are evaluated in the framework of NRQCD sum rules. The coulomb-like corrections in the system of doubly heavy diquark are taken into account, and the contribution of nonperturbative terms coming from the quark, gluon and mixed condensates as well as the product of quark and gluon condensates, is analyzed. The higher condensates destroy the factorization of baryon and diquark correlators and provide the convergency of sum rule method. As a result the accuracy of estimates is improved.

Inclusive decays and lifetimes of doubly-charmed baryons

The analysis of singly-charmed hadrons has been extended to the case of doubly-charmed baryons, $\Xi_{cc}^{++}$ , $\Xi_{cc}^{+}$ and $\Omega_{cc}^{+}$ . Doubly-charmed baryons are described as a system containing a heavy cc diquark and a light quark, as in the case of a heavy–light meson. This leads to preasymptotic effects in semileptonic and nonleptonic decays that are essentially proportional to the meson wave function. Interplay between preasymptotic effects in semileptonic and/or nonleptonic decay rates leads to very clear predictions for semileptonic branching ratios and lifetimes of doubly-charmed baryons.

Weak semileptonic decays of heavy baryons containing two heavy quarks

In the heavy quark limit a heavy baryon which contains two heavy quarks is believed to be composed of a heavy diquark and a light quark. Based on this picture, we evaluate the weak semileptonic decay rates of such baryons. The transition form factors between two heavy baryons are associated with those between two heavy mesons by applying superflavor symmetry. The effective vertices of the W boson and two heavy diquarks are obtained in terms of the Bethe-Salpeter equation. Numerical predictions on these semileptonic decay widths are presented and they will be tested in future experiments.

Photonic production ofS- andP-waveB c states and doubly heavy baryons

Numerical calculations for the production ofS-andP-wave levels ofBc quarkonium inγγ collisions are performed in the leadingO(αs2αem2) order of perturbation theory. The total cross-section ofP-wave state production is about 10 % of that for theS-wave levels. The contribution of fragmentation component (6+6 diagrams) is low, and the basic contribution is determined by the recombination mechanism (8 Feynman diagrams). The gauge invariant term of the\(\bar b\)→Bc fragmentation (6 diagrams) quite accurately reproduces the result of the fragmentation model, whereas there is a strong deviation of thec→Bc fragmentation term from the predictions of the fragmentation model. The total cross-sections in photonic production of doubly heavy diquark, hadronizing into the baryons, are evaluated.

Heavy diquark contributions to multijet production at the Z 0 peak

We calculate the contribution of a superstring-inspired heavy diquark to the four-jet rate in e +e − collisions. We find that Z-decay data with charm-quark tagging, corresponding to an integrated luminocity of 20–100 pb −1, will set a bound of 50–60 GeV on the diquark mass. We argue that this is a rather model-independent result.

Jet signatures of scalar diquarks from superstrings at e −e + colliders

We determine the 4-jet contribution in e −e + collisions of heavy scalar diquarks from E 6 compactification in superstring theories. For CM energy √ s>150 GeV the signal exceeds the QCD background (for √ s>200 Gev by an order of magnitude or more). At the Z 0 peak the background somewhat exceeds the signal, but we show that measured cross sections are sensitive to this contribution for diquark masses up to ∼ 45 GeV.