Bottom Baryons Research Articles

Identifying the Λb(6146)0 and Λb(6152)0 as D-Wave Bottom Baryons

We study the Λ b ( 6146 ) 0 and Λ b ( 6152 ) 0 recently observed by LHCb using the method of Quantum Chromodynamics (QCD) sum rules within the framework of heavy quark effective theory. Our results suggest that they can be interpreted as D-wave bottom baryons of J P = 3 / 2 + and 5 / 2 + respectively, both of which contain two λ -mode excitations. We also investigate other possible assignments containing ρ -mode excitations. We extract all the parameters that are necessary to study their decay properties when using the method of light-cone sum rules. We predict masses of their strangeness partners to be m Ξ b ( 3 / 2 + ) = 6.26 − 0.14 + 0.11 GeV and m Ξ b ( 5 / 2 + ) = 6.26 − 0.14 + 0.11 GeV with the mass splitting Δ M = m Ξ b ( 5 / 2 + ) − m Ξ b ( 3 / 2 + ) = 4.5 − 1.5 + 1.9 MeV, and propose to search for them in future CMS, EIC, and LHCb experiments.

P -wave bottom baryons of the SU(3) flavor 6F

We investigate P-wave bottom baryons of the SU(3) flavor 6F, and systematically study their D-wave decays into ground-state bottom baryons and pseudoscalar mesons. Together with [H. X. Chen et al., Phys. Rev. D 91, 054034 (2015)PRVDAQ1550-799810.1103/PhysRevD.91.054034; Q. Mao et al., Phys. Rev. D 92, 114007 (2015)PRVDAQ1550-799810.1103/PhysRevD.92.114007; H. X. Chen et al., Phys. Rev. D 95, 094008 (2017)PRVDAQ2470-001010.1103/PhysRevD.95.094008; H. M. Yang et al.,Eur. Phys. J. C 80, 80 (2020)EPCFFB1434-604410.1140/epjc/s10052-020-7637-z], a rather complete study is performed on both mass spectra and decay properties of P-wave bottom baryons, using the method of QCD sum rules and light-cone sum rules within the framework of heavy quark effective theory. Among all the possibilities, we find four Σb, four Ξb′, and six Ωb baryons, with limited widths and so capable of being observed. Their masses, mass splittings within the same multiplets, and decay properties are extracted (summarized in Table VI) for future experimental searches.

Roper-like resonances with various flavor contents and their two-pion emission decays

We study the three-body decay of the newly observed bottom baryon $\Lambda_b^*(6072)$ by LHCb; $\Lambda_b^*(6072) \to \Lambda_b \pi \pi$. Its mass about 500 MeV above the ground state $\Lambda_b$ and a broad width imply that the state could be an analogue of the Roper resonance of the nucleon $N(1440)$. In terms of sequential processes going through $\Sigma_b$ and $\Sigma_b^*$, we find that the observed invariant mass distribution is reproduced assuming its spin and parity $J^P = 1/2^+$. We discuss that the ratio of the two sequential processes and angular correlation of two pions are useful for the determination of spin and parity. We suggest further studies for the Roper resonance analogue in various flavor contents, raising an interesting and important question in baryon spectroscopy.

Heavy baryon spectrum on the lattice with NRQCD bottom and HISQ lighter quarks

We determine the mass spectra of heavy baryons containing one or more bottom quarks along with their hyperfine splittings and various mass differences on MILC 2+1 Asqtad lattices at three different lattice spacings. NRQCD action is used for bottom quarks whereas relativistic HISQ action for the lighter up/down, strange and charm quarks. We consider all possible combinations of bottom and lighter quarks to construct the bottom baryon operators for the states $J^P=1/2^+$ and $3/2^+$.

Triply charmed and bottom baryons in a constituent quark model

In this work, we study the mass spectrum of the $\Omega_{ccc}$ and $\Omega_{bbb}$ baryons up to the $N=2$ shell within a nonrelativistic constituent quark model (NRCQM). The model parameters are adopted from the determinations by fitting the charmonium and bottomonium spectra in our previous works. The masses of the $\Omega_{ccc}$ and $\Omega_{bbb}$ baryon states predicted in present work reasonably agree with the results obtained with the Lattice QCD calculations. Furthermore, to provide more knowledge of the $\Omega_{ccc}$ and $\Omega_{bbb}$ states, we evaluate their radiative decays with the available masses and wave functions from the potential model.

Λb(6146)0 state newly observed by LHCb

We study the bottom $\Lambda_b(6146)^0$ baryon, newly discovered by the LHCb Collaboration. By adopting an interpolating current of $(L_{\rho}, L_{\lambda})=(0,2)$ type and $D$-wave nature with spin-parity quantum numbers $J^P=\frac{3}{2}^+$ for this heavy bottom baryon, we calculate its mass and residue. Using these spectroscopic parameters, we also investigate its dominant decays $\Lambda_b(6146)^0\rightarrow\Sigma_b\pi$ and $\Lambda_b(6146)^0\rightarrow\Sigma^*_b\pi$ and estimate the width of $\Lambda_b(6146)^0$ obtained via these channels. The obtained mass, $m_{\Lambda_b}=(6144\pm 68)$~MeV is in accord nicely with the experimental data. The width obtained via the dominant channels is also consistent with the experimental data of LHCb collaboration. We calculate the spectroscopic parameters and the same decay channels for the $c$-partner of $\Lambda_b(6146)^0$ state, namely $\Lambda_c(2860)^+$, as well. We compare the obtained results with the existing theoretical predictions as well as experimental data. The results indicate that the state $\Lambda_b(6146)^0$ and its charmed-partner $\Lambda_c(2860)^+$ can be considered as $1D$-wave baryons with $J^P=\frac{3}{2}^+$.

Regge behaviors in orbitally excited spectroscopy of charmed and bottom baryons

Stimulated by recent progress made by the LHCb Collaboration in discoveries of new bottom baryons, e.g., the $\Xi _{b}(6227)^{-}$ and the $\Sigma_{b}(6097)^{\pm}$, we re-examine the orbitally excited spectrum of the charmed and bottom baryons using Regge approach in the heavy quark-diquark picture. The results indicate that the spin-averaged mass spectrum of the orbitally-excited charmed and bottom baryons can be described by a linear Regge relation, which is derived from the rotating QCD string model. By giving further mass-splitting analysis of spin-dependent interactions, we explain the baryons $\Xi_{b}(6227)^{-}$ and the $\Sigma_{b}(6097)^{\pm}$,and the $\Sigma _{c}(2800)$ and $\Xi _{c}^{\prime }(2930)$ to be the $1P$%-wave baryons, all with the spin-parity $J^{P}=3/2^{-}$ preferably. Mass prediction of the bottom baryon $\Xi_{b}$ in its P- and D-waves are presented, providing clues for the coming experiments like the LHCb to find them.

Decay properties of P-wave bottom baryons within light-cone sum rules

We use the method of light-cone sum rules to study decay properties of P-wave bottom baryons belonging to the SU(3) flavor mathbf {6}_F representation. In Cui et al. (Phys Rev D 99:094021, 2019) we have studied their mass spectrum and pionic decays, and found that the varSigma _{b}(6097) and varXi _{b}(6227) can be well interpreted as P-wave bottom baryons of J^P = 3/2^-. In this paper we further study their decays into ground-state bottom baryons and vector mesons. We propose to search for a new state varXi _b({5/2}^-), that is the J^P = 5/2^- partner state of the varXi _{b}(6227), in the varXi _b({5/2}^-) rightarrow varXi _b^{*}rho rightarrow varXi _b^{*}pi pi decay process. Its mass is 12 pm 5 MeV larger than that of the varXi _{b}(6227).

Bottom (70,1-) baryon multiplet

The aim of this paper is to derive systems of equations for the amplitudes for the case of negative parity (70,1-) bottom nonstrange baryons and to calculate the masses of these particles. In order to calculate masses of (70,1-) bottom baryons we use the relativistic quark model. The relativistic three-quark equations of the (70,1-) bottom baryon multiplet are derived in the framework of the dispersion relation technique. The relativistic three-quark equations of the (70,1-) bottom baryon multiplet are derived. The approximate solutions of these equations using the method based on the extraction of leading singularities of the amplitude are obtained. The masses of 21 baryons are predicted.

Describing a Baryon as a Meson Pair

We propose a new description of a baryon as a pair of mesons. This description is an extension of the previously proposed description of a nucleon as a pair of pions. The purpose of this article is to show the following two possibilities. The first one is that it shows the qualitative explanation to support our description of a nucleon as a pair of pions and the second one is that it gives the systematic way of estimation of baryon mass not only for light baryons but also for heavy baryons (charm baryons and bottom baryons). Each isospin group is constructed of both baryons and antibaryons. This way of construction is consistent with that of mesons. The results obtained are listed in tables (Tables 1-9). This shows that the generalized Gell-Mann-Nishijima relation equation holds under the condition that the baryon number is 0 and that the obtained masses are fairly good, even for heavy baryons. Our description also yields several examples of baryon decay modes.

Interpretation of the observed Λb(6146)0 and Λb(6152)0 states as 1D bottom baryons

The measured masses and strong decays of $\Lambda_b(6146)^0$ and $\Lambda_b(6152)^0$ required us to decode them as the 1$D$ excited states with $J^P=3/2^+$ and $J^P=5/2^+$, respectively. Under the suggested assignment, the masses and total decay widths of $\Lambda_b(6146)^0$ and $\Lambda_b(6152)^0$ can be explained. As a $J^P=3/2^+$ state, the $\Lambda_b(6146)^0$ should mainly decay into $\Sigma_b(5815)\pi$. However, this theoretical result is in contradiction to the measurement since no significant $\Lambda_b(6146)^0\rightarrow\Sigma_b(5815)^\pm\pi^\mp$ signals were observed by the LHCb. The possible explanations to this difficulty are mentioned. For completeness, we present the prediction of masses and decay widths of other unseen 1$D$ bottom baryons in this work. Our results could provide some important clues for the upcoming experiments.

Phenomenological predictions for pentaquark masses from fits to baryon masses

We investigate the mass spectra of exotic hadrons known as pentaquarks. We extend a simple phenomenological model based on the Gürsey–Radicati mass formula for hadrons to include both charmed and bottom baryons as well as to be able to predict masses of pentaquark states including both charm and bottom quark-antiquark pairs. In particular, we perform numerical fits of this model, which includes seven free parameters, to masses of 21 baryons. We find that the model can be well fitted to the experimental values of the baryon masses and observe that the predicted value of about 4400 MeV for the mass of the pentaquark Pc(4380)+ lies within the experimental range reported by the LHCb experiment. In addition, the predicted value of about 4500 MeV for the mass of the pentaquark Pc(4450)+ is close to the experimental value. Finally, in the future, other predicted values for masses of additional pentaquarks could be shown to agree with upcoming experimental results.

Status of isospin splittings in mesons and baryons

Current measurements of isospin splittings in mesons and baryons are sufficiently precise that they allow estimates of the mass difference between constituent up and down quarks. Some previous results are updated in the light of these new measurements, and the importance of better measurements of some observables such as $M(K^{*\pm})$, $M(B^{*0})-M(B^0)$, and isospin splittings in bottom baryons is noted.

Canonical interpretation of the newly observed Λb(6146)0 and Λb(6152)0 via strong decay behaviors

Stimulated by the newly observed ${\mathrm{\ensuremath{\Lambda}}}_{b}(6146{)}^{0}$ and ${\mathrm{\ensuremath{\Lambda}}}_{b}(6152{)}^{0}$ resonances, we investigate the strong decays of the low-lying singly bottom baryons within the quark pair creation model. Considering their masses and decay modes, we tentatively assign these states as the $\ensuremath{\lambda}$-mode ${\mathrm{\ensuremath{\Lambda}}}_{b}(2S)$, ${\mathrm{\ensuremath{\Lambda}}}_{b}(1D)$, ${\mathrm{\ensuremath{\Sigma}}}_{b}(2S)$, and ${\mathrm{\ensuremath{\Sigma}}}_{b}(1P)$ states and then estimate their strong decay widths. Compared with the experimental total widths and decay modes measured by the LHCb Collaboration, the ${\mathrm{\ensuremath{\Lambda}}}_{b}(6146{)}^{0}$ and ${\mathrm{\ensuremath{\Lambda}}}_{b}(6152{)}^{0}$ can be reasonably clarified into the ${J}^{P}=5/{2}^{+}$ and ${J}^{P}=3/{2}^{+}$ ${\mathrm{\ensuremath{\Lambda}}}_{b}(1D)$ states, respectively, while other canonical assignments are disfavored. Other low-lying bottom states are also presented, where various narrow states may have good potential to be observed in future LHCb experiments.

Identifying the Ξb(6227) and Σb(6097) as P -wave bottom baryons of JP=3/2−

We use the method of QCD sum rules within the framework of heavy quark effective theory to study the mass spectrum of the $\Sigma_{b}(6097)^{\pm}$ and $\Xi_{b}(6227)^{-}$, and use the method of light-cone sum rules still within the heavy quark effective theory to study their decay properties. Our results suggest that they can be well interpreted as $P$-wave bottom baryons with the spin-parity $J^P = 3/2^-$. They belong to the baryon doublet $[\mathbf{6}_F, 2, 1, \lambda]$, where the total and spin angular momenta of the light degree of freedom are $j_l = 2$ and $s_l = 1$, and the orbital angular momentum is between the bottom quark and the two-light-quark system ($\lambda$-type). This doublet contains six bottom baryons, and we predict masses (mass differences) and decay widths of the other four states to be $M_{\Omega_b(3/2^-)} = 6.46 \pm 0.12 {~\rm GeV}$, $\Gamma_{\Omega_b(3/2^-)} = 58{^{+65}_{-33}} {~\rm MeV}$, $M_{\Sigma_b(5/2^-)}-M_{\Sigma_b(3/2^-)}= 13 \pm 5 {~\rm MeV}$, $M_{\Xi_b^{\prime}(5/2^-)}-M_{\Xi_b^{\prime}(3/2^-)} = 12 \pm 5 {~\rm MeV}$, and $M_{\Omega_b(5/2^-)}-M_{\Omega_b(3/2^-)} = 11 \pm 5 {~\rm MeV}$. We propose to search for them in further LHCb experiments.

Lifetimes of doubly heavy baryons Bbb and Bbc

Lifetimes of the doubly heavy baryons ${\cal B}_{bb}$ and ${\cal B}_{bc}$ are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from the spectator effects such as $W$-exchange and Pauli interference. For doubly bottom baryons, the lifetime pattern is $\tau(\Omega_{bb}^-)\sim \tau(\Xi_{bb}^{-})>\tau(\Xi_{bb}^0)$. The $\Xi_{bb}^{0}$ baryon is shortest-lived owing to the $W$-exchange contribution, while $\Xi_{bb}^{-}$ and $\Omega_{bb}^{-}$ have similar lifetimes as they both receive contributions from destructive Pauli interference. We find the lifetime ratio $\tau(\Xi_{bb}^{-})/\tau(\Xi_{bb}^0)=1.26$\,. The large $W$-exchange contribution to $\Xi_{bc}^0$ through the subprocess $cd\to us\to cd$ and the sizable destructive Pauli interference contribution to $\Xi_{bc}^+$ imply a substantial lifetime difference between $\Xi_{bc}^+$ and $\Xi_{bc}^0$. In the presence of subleading $1/m_c$ and $1/m_b$ corrections to the spectator effects, we find that $\tau(\Omega_{bc}^0)$ becomes longest-lived. This is because $\Gamma^{\rm int}_+$ and $\Gamma^{\rm semi}$ for $\Omega_{bc}^0$ are subject to large cancellation between dimension-6 and -7 operators. This implies that the subleading corrections are too large to justify the validity of the HQE. Demanding that $\Gamma^{cs}_{{\rm int+}}(\Omega_{bc}^0)$, $\Gamma^{{\rm SL},cs}_{\rm int}(\Omega_{bc}^0)$ be positive and $\Gamma^{cu}_{{\rm int-}}(\Xi^+_{bc})$ be negative, we conjecture that $1.68\times 10^{-13}s<\tau(\Omega_{bc}^0)< 3.70\times 10^{-13}s$ , $4.09\times 10^{-13}s<\tau(\Xi_{bc}^+)< 6.07\times 10^{-13}s$ and $0.93\times 10^{-13}s<\tau(\Xi_{bc}^0)< 1.18\times 10^{-13}s$. Hence, the lifetime hierarchy of ${\cal B}_{bc}$ baryons is expected to be the pattern $\tau(\Xi_{bc}^{+})>\tau(\Omega_{bc}^0)>\tau(\Xi_{bc}^0)$.

Excited mesons, baryons, glueballs and tetraquarks: predictions of the Holography Inspired Stringy Hadron model

In this note we collect and summarize the predictions of the Holography Inspired Stringy Hadron (HISH) model. Following a brief review of the model, we list the masses and widths of predicted excited states across the spectrum, based on placing the different hadrons on the non-linear Regge trajectories of a string with massive endpoints. Our predicted states include: (i) Light, heavy–light and heavy–heavy mesons. (ii) Baryons, including charmed, doubly charmed and bottom baryons. (iii) Glueballs, together with a method to disentangle them from flavorless mesons. (iv) Genuine tetraquarks, which are not “molecules” of hadrons, and are characterized by their decay into a baryon and an anti-baryon.

Radiative decays of the singly heavy baryons in chiral perturbation theory

In the framework of the heavy baryon chiral perturbation theory (HBChPT), we calculate the radiative decay amplitudes of the singly heavy baryons up to the next-to-next-to-leading order (NNLO). In the numerical analysis, we adopt the heavy quark symmetry to relate some low energy constants (LECs) with those LECs in the calculation of the magnetic moments. We use the results from the lattice QCD simulation as input. With a set of unified LECs, we obtain the numerical (transition) magnetic moments and radiative decay widths. We give the numerical results for the spin-$1\over 2$ sextet to the spin-$1\over 2$ antitriplet up to the next-to-leading order (NLO). The nonvanishing $\Gamma(\Xi_c^{'0} \rightarrow \Xi^0_c\gamma)$ and $\Gamma(\Xi_c^{*0} \rightarrow \Xi^0_c \gamma)$ solely arise from the U-spin symmetry breaking, and do not depend on the lattice QCD inputs up to NLO. We also systematically give the numerical analysis of the magnetic moments of the spin-$1\over 2$, spin-$3\over 2$ sextet and their radiative decay widths up to NNLO. In the heavy quark limit, the radiative decays between the sextet states happen through the magnetic dipole (M1) transitions, while the electric quadrupole (E2) transition does not contribute. We also extend the same analysis to the single bottom baryons.

Color-allowed bottom baryon to charmed baryon nonleptonic decays

We study color allowed $\Lambda_b\to \Lambda^{(*,**)}_c M^-$, $\Xi_b\to\Xi_c^{(**)} M^-$ and $\Omega_b\to\Omega^{(*)}_c M^-$ decays with $M=\pi, K,\rho, K^*, D, D_s, D^*, D^*_s, a_1$, $\Lambda^{(*,**)}_c=\Lambda_c$, $\Lambda_c(2595)$, $\Lambda_c(2765)$, $\Lambda_c(2940)$, $\Xi_c^{(**)}=\Xi_c, \Xi_c(2790)$ and $\Omega^{(*)}_c=\Omega_c, \Omega_c(3090)$, in this work. There are three types of transitions, namely ${\cal B}_b({\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},1/2^+)$, ${\cal B}_b({\bf 6_f},1/2^+)$ to ${\cal B}_c({\bf 6_f},1/2^+)$ and ${\cal B}_b({\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},1/2^-)$ transitions. The bottom baryon to charmed baryon form factors are calculated using the light-front quark model. Decay rates and up-down asymmetries are predicted using na\"{i}ve factorization and can be checked experimentally. We find that in ${\cal B}_b\to {\cal B}_cP$ decays, rates in type~(ii) transition are smaller than those in type (i) transition, but similar to those in type (iii) transition, while in ${\cal B}_b\to{\cal B}_c V, {\cal B}_c A$ decays, rates in type~(ii) transition are much smaller than those in type (i) transition and are also smaller than those in type (iii) transition. For the up-down asymmetries, the signs are mostly negative, except for those in the type (ii) transition. All of these asymmetries are large in sizes. The study on these decay modes may shed light on the quantum numbers of some of the charmed baryons as the decays depend on the bottom baryon to charmed baryon form factors, which are sensitive to the configurations of the final state charmed baryons.

In-medium properties of the low-lying strange, charm, and bottom baryons in the quark-meson coupling model

In-medium properties of the low-lying strange, charm, and bottom baryons in symmetric nuclear matter are studied in the quark-meson coupling (QMC) model. Results for the Lorentz-scalar effective masses, mean field potentials felt by the light quarks in the baryons, in-medium bag radii, and the lowest mode bag eigenvalues are presented for those calculated using the updated data. This study completes the in-medium properties of the low-lying baryons in symmetric nuclear matter in the QMC model, for the strange, charm and bottom baryons which contain one or two strange, one charm or one bottom quarks, as well as at least one light quark. Highlight is the prediction of the bottom baryon Lorentz-scalar effective masses, namely, the Lorentz-scalar effective mass of $\Sigma_b$ becomes smaller than that of $\Xi_b$ at moderate nuclear matter density, $m^*_{\Sigma_b} < m^*_{\Xi_b}$, although in vacuum $m_{\Sigma_b} > m_{\Xi_b}$. We study further the effects of the repulsive Lorentz-vector potentials on the excitation (total) energies of these bottom baryons.