Static properties and semileptonic transitions of lowest-lying double heavy baryons

The static properties and semileptonic decays of ground-state doubly heavy baryons are studied in the framework of a non-relativistic quark model. Using a phenomenological potential model, we calculate the ground-state masses and magnetic moments of doubly heavy Ω and Ξ baryons. In the heavy quark limit, we introduce a simple form of the universal Isgur-Wise function used as the transition form factor and then investigate the exclusive \begin{document}$ b \rightarrow c $\end{document} semileptonic decay widths and branching fractions for \begin{document}$ \dfrac{1}{2}\rightarrow \dfrac{1}{2} $\end{document} baryon transitions. Our obtained results are in agreement with other theoretical predictions.     

Charmed baryons circa 2015

This is essentially an update of Ref. [1] [H. Y. Cheng, Int. J. Mod. Phys. A 24 (Suppl. 1), 593 (2009)], a review of charmed baryon physics around 2007. Topics covered in this review include the spectroscopy, strong decays, lifetimes, nonleptonic and semileptonic weak decays, and electromagnetic decays of charmed baryons.     

Study of Doubly Heavy Baryon Spectrum via QCD Sum Rules

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.     

Lifetime of Doubly Charmed Baryons

In this work, we evaluate the lifetimes of the doubly charmed baryons Ξcc^＋ ,Ξcc^＋＋, and Ωcc^＋. We carefully calculate the non-spectator contributions at the quark level, where the Cabibbo-suppressed diagrams are also included. The hadronic matrix elements are evaluated in the simple non-relativistic harmonic oscillator model. Our numerical results are generally consistent with that obtained by other authors who used the diquark model. However, all the theoretical predictions on the lifetimes are one order larger than the upper limit set by the recent SELEX measurement. This discrepancy would be clarified by the future experiment. If more accurate experiment still confirms the value of the SELEX collaboration, there must be some unknown mechanism to be explored.     

Spectra of charmed and bottom baryons with hyperfine interaction

Up to now,the excited charmed and bottom baryon states have still not been well studied experimentally or theoretically.In this paper,we predict the mass of ?*b,the only L=0 baryon state which has not been observed,to be 6069.2 Me V.The spectra of charmed and bottom baryons with the orbital angular momentum L = 1 are studied in two popular constituent quark models,the Goldstone boson exchange(GBE) model and the one gluon exchange(OGE) hyperfine interaction model.Inserting the latest experimental data from the "Review of Particle Physics",we find that in the GBE model,there exist some multiplets(Σc(b),Ξ c(b)and ?c(b)) in which the total spin of the three quarks in their lowest energy states is 3/2,but in the OGE model there is no such phenomenon.This is the most important difference between the GBE and OGE models.These results can be tested in the near future.We suggest more efforts to study the excited charmed and bottom baryons both theoretically and experimentally,not only for the abundance of baryon spectra,but also for determining which hyperfine interaction model best describes nature.     

Triply heavy baryons in the constituent quark model

The constituent quark model is used to compute the ground and excited state masses of QQQ baryons containing either c or b quarks.The quark model parameters previously used to describe the properties of charmonium and bottomonium states were used in this analysis.The non-relativistic three-body bound state problem is solved by means of the Gaussian expansion method which provides sufficient accuracy and simplifies the subsequent evaluation of the matrix elements.Several low-lying states with quantum numbers J^P=1/2^±,3/2^±,5/2^±and 7/2^+are reported.We compare the results with those obtained by the other theoretical formalisms.There is a general agreement for the mass of the ground state in each sector of triply heavy baryons.However,the situation is more puzzling for the excited states,and appropriate comments about the most relevant features of our comparison are given.     

Exotic pentaquarks as Gamov-Teller resonances

If the number of colors N c is taken large,baryons and their excitations can be considered in a mean-field approach.We argue that the mean field in baryons breaks spontaneously the spherical and SU(3) flavor symmetries,but retains the SU(2) symmetry of simultaneous rotations in space and isospace.The one-quark and quark-hole excitations in the mean field,together with the SU(3) rotational bands about them determine the spectrum of baryon resonances,which turns out to be in good accordance with reality when one puts N c =3.A by-product of this scheme is a confirmation of the light pentaquark Θ + baryon uudds as a typical Gamov–Teller resonance long known in nuclear physics.An extension of the same large-N c logic to charmed baryons leads to a prediction of a anti-decapenta (15)-plet of charmed pentaquarks,two of which,B ++ c = cuuds and B + c = cudds,may be light and stable with respect to strong decays.     

Negative elliptic flow of J/ψ’s: A qualitative signature for charm collectivity at RHIC

We discuss one of the most prominent features of the very recent preliminary elliptic flow data of J/ψ-mesons from the PHENIX Collaboration (PHENIX Collaboration (C. Silvestre), arXiv:0806.0475 [nucl-ex]). Even within the rather large error bars of the measured data a negative elliptic flow parameter (v₂) for J/ψ in the range of p _T = 0.5-2.5 GeV/c is visible. We argue that this negative elliptic flow at intermediate p_T is a clear and qualitative signature for the collectivity of charm quarks produced in nucleus-nucleus reactions at RHIC. Within a parton recombination approach we show that a negative elliptic flow puts a lower limit on the collective transverse velocity of heavy quarks. The numerical value of the transverse flow velocity for charm quarks that is necessary to reproduce the data is (charm) ∼ 0.55-0.6c and therefore compatible with the flow of light quarks.     

Baryon resonance analysis from MAID

The unitary isobar model MAID2007 has been used to analyze the recent data of pion electroproduction. The model contains all four-star resonances in the region below W = 2 GeV and both single-Q~2 and Q~2 dependent transition form factors could be obtained for the Delta, Roper, D_(13)(1520), S_(11) (1535), S_(31) (1620), S_(11)(1650), D_(15)(1675), F_(15)(1680) and P_(13)(1720). From the complete world data base, including also π~- data on the neutron, also Q~2 dependent neutron form factors are obtained. For all transition form factors we also give convenient numerical parameterizations that can be used in other reactions. Furthermore, we show how the transition form factors can be used to obtain empirical transverse charge densities and our first results are given for the Roper, the S_(11) and D_(13) resonances.     

J~P assignments of Λ_c~+ baryons

The "good" diquark is employed to study Λ_c~+ baryons within a mass loaded flux tube model. The study indicates that all Λ_c~+ baryons candidates in the 2008 review by the Particle Data Group (PDG) are well described in the mass loaded flux model. The quantum numbers J~P of these Λ_c~+ candidates are assigned. If Λ_c(2765)~+ is an orbitally excited Λ_c~+, it is likely the J~P=3~+/2 one. If Λ_c(2765)~+ is an orbitally excited Σ_c, there ought to be another J~P = 3~+/2 Λ_c~+ with mass ≈ 2770 MeV. In the model, there exists no J~P = 1~+/2 Λ_c~+ (≈ 2700) predicted in existing literature. Λ_c(2940)~+ is very possible the orbitally excited baryon with J~P = 5~-/2.