Quark Spin Research Articles

Zb tetraquark channel from lattice QCD and Born-Oppenheimer approximation

Two Zb hadrons with exotic quark structure b¯bd¯u were discovered by Belle experiment. We present a lattice QCD study of the b¯bd¯u system in the approximation of static b quarks, where the total spin of heavy quarks is fixed to one. The energies of eigenstates are determined as a function of the separation r between b and b¯. The lower eigenstates are related to a bottomonium and a pion. The eigenstate dominated by BB¯⁎ has energy significantly below mB+mB⁎, which points to a sizable attraction for small r. The attractive potential V(r) between B and B¯⁎ is extracted assuming that this eigenstate is related exclusively to BB¯⁎. The Schrödinger equation for BB¯⁎ within the extracted potential leads to one bound state below BB¯⁎ threshold, whose mass depends on the parametrization of the lattice potential. For certain parametrizations, the bound state is very close to the BB¯⁎ threshold and renders a narrow peak in the BB¯⁎ rate above threshold - these features could be related to Zb(10610) in the experiment.

Decuplet baryons in nuclear and hyperonic medium

Masses and the magnetic moments of baryon decuplet are evaluated in the symmetric nuclear and hyperonic matter at finite temperature using a chiral SU(3) quark mean field model approach. The decuplet baryon masses considerably decrease with the rise in the baryonic density of the medium. With the increase in strangeness (more number of hyperons as compared to nucleons) fraction, the non-strange baryons show an increase in their masses, whereas the strange baryons show a decrease. The contributions coming from the valence quarks, quark sea and the orbital angular momentum of the quark sea have been considered to calculate net magnetic moment. The magnetic moments of decuplet baryons are found to show a considerable increase with the baryonic density of the medium since constituent quark magnetic moment and the quark spin polarizations show significant variation in the nuclear medium especially in the low temperature and baryonic density regime. The increase is however quantitatively less as compared to the case of octet baryon members. With the inclusion of hyperons along with nucleons, the non-strange baryons show a decrease in the magnitude of their effective magnetic moments, whereas the strange baryons show an increase. The strangeness fraction of the medium is found to largely affect the valence quark magnetic moment and quark sea magnetic moment of the baryons.

Interpretation of the LHCb P_{c} States as Hadronic Molecules and Hints of a Narrow P_{c}(4380).

Three hidden-charm pentaquark P_{c} states, P_{c}(4312), P_{c}(4440), and P_{c}(4457) were revealed in the Λ_{b}^{0}→J/ψpK^{-} process measured by LHCb using both run I and run II data. Their nature is under lively discussion, and their quantum numbers have not been determined. We analyze the J/ψp invariant mass distributions under the assumption that the crossed-channel effects provide a smooth background. For the first time, such an analysis is performed employing a coupled-channel formalism with the scattering potential involving both one-pion exchange as well as short-range operators constrained by heavy quark spin symmetry. We find that the data can be well described in the hadronic molecular picture, which predicts seven Σ_{c}^{(*)}D[over ¯]^{(*)} molecular states in two spin multiplets, such that the P_{c}(4312) is mainly a Σ_{c}D[over ¯] bound state with J^{P}=1/2^{-}, while P_{c}(4440) and P_{c}(4457) are Σ_{c}D[over ¯]^{*} bound states with quantum numbers 3/2^{-} and 1/2^{-}, respectively. We also show that there is evidence for a narrow Σ_{c}^{*}D[over ¯] bound state in the data which we call P_{c}(4380), different from the broad one reported by LHCb in 2015. With this state included, all predicted Σ_{c}D[over ¯], Σ_{c}^{*}D[over ¯], and Σ_{c}D[over ¯]^{*} hadronic molecules are seen in the data, while the missing three Σ_{c}^{*}D[over ¯]^{*} states are expected to be found in future runs of the LHC or in photoproduction experiments.

Relaxation time for strange quark spin in rotating quark-gluon plasma

Experiments at the Relativistic Heavy Ion Collider (RHIC) have measured the net polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons and attributed it to a coupling between their spin and the vorticity of the fluid created in heavy ion collisions. Equipartition of energy is generally assumed, but the dynamical mechanism which polarizes them has yet to be determined. We consider two such mechanisms: vorticity fluctuations and helicity flip in scatterings between strange quarks and light quarks and gluons. With reasonable parameters both mechanisms lead to equilibration times orders of magnitude too large to be relevant to heavy ion collisions. Our conclusion is that strange quark spin or helicity is unchanged from the time they are created to the time they hadronize. A corollary is that vorticity fluctuations do not affect the hyperon spin either.

Study of Spin–Spin Correlations between Quark and a Spin-1/2 Composite System

We study the correlation between the fermion composite system and quark spins by using the light-cone quark–diquark model. We do the calculations for u-quark and d-quark in the fermion system by considering different polarization configurations of both. The contribution from scalar and axial-vector diquarks is taken into account. The overlap representation of light-front wavefunctions is used for the calculations. The spin–spin correlations for u and d quarks are presented in transverse impact-parameter plane and transverse momentum plane as well.

Nature of the lowest-lying odd parity charmed baryon Λc(2595) and Λc(2625) resonances

We study the structure of the $\Lambda_c(2595)$ and $\Lambda_c(2625)$ resonances in the framework of an effective field theory consistent with heavy quark spin and chiral symmetries, that incorporates the interplay between $\Sigma_c^{(*)}\pi-ND^{(*)}$ baryon-meson degrees of freedom and bare P-wave $c\bar ud$ quark-model states. We show that these two resonances are not HQSS partners. The $J^P= 3/2^-$ $\Lambda_c(2625)$ should be viewed mostly as a dressed three quark state, whose origin is determined by a bare state, predicted to lie very close to the mass of the resonance. The $J^P= 1/2^-$ $\Lambda_c(2595)$ seems to have, however, a predominant molecular structure. This is because, it is either the result of the chiral $\Sigma_c\pi$ interaction, which threshold is located much more closer than the mass of the bare three-quark state, or because the light degrees of freedom in its inner structure are coupled to the unnatural $0^-$ quantum-numbers. We show that both situations can occur depending on the renormalization procedure used. We find some additional states, but the classification of the spectrum in terms of HQSS is difficult, despite having used interactions that respect this symmetry. This is because the bare quark-model state and the $\Sigma_c\pi$ threshold are located extraordinarily close to the $\Lambda_c(2625)$ and $\Lambda_c(2595)$, respectively, and hence they play totally different roles in each sector.

Constituent quark mass and spin in NRCQM model

We show that the success of the Nonrelativistic Constituent Quark Model can be associated with symmetrization, which manifests itself in the exact 3:1 ratio between the initial constituent quark mass Mq = mΞ/3=441MeV and the parameter of quark interaction ΔMΔ = (mΔ − mN)/2=147MeV. The interconnection of these parameters with the electron mass, its symmetry, the masses of the fundamental fields and the QED radiative correction is considered. The discreteness with the parameter me can be used in the study of gravitation and dark matter problems.

Spin polarizations under a pseudovector interaction between quarks with the Kobayashi–Maskawa–’t Hooft term in high density quark matter

A possibility of a quark spin polarization originating from a pseudovector condensate is investigated in the three-flavor Nambu–Jona–Lasinio model with the Kobayashi–Maskawa–’t Hooft interaction which leads to flavor mixing. It is shown that a pseudovector condensate related to the strange quark easily occurs compared with pseudovector condensate related to light quarks. Further, it is shown that the pseudovector condensate related to the strange quark appears at a slightly small chemical potential by the effect of the flavor mixing due to the Kobayashi–Maskawa–’t Hooft interaction.

Relaxation time for quark spin and thermal vorticity alignment in heavy-ion collisions

We compute the relaxation time for quark/antiquark spin and thermal vorticity alignment in a quark-gluon plasma at finite temperature and quark chemical potential. We model the interaction of quark/antiquark spin with thermal vorticity as driven by a phenomenological modification of the elementary quark interaction with gluons. We find that in a scenario where the angular velocity of the quark-gluon plasma produced in a peripheral heavy-ion collision is small, quarks/antiquarks take a long time to align their spin with the vorticity. However, when the angular velocity created in the reaction is large, the alignment is efficient and well within the lifetime of the system created in the reaction. The relaxation time is larger for antiquarks which points out to a difference for the polarization of hadrons and antihadrons when this alignment is preserved during hadronization.

Predictions of transitions * * Supported in part by the Fundamental Research Funds for the Central Universities (FRF-BR-19-001A), and by the National Natural Science Foundation of China (11975028)

We study the contributions of intermediate bottomonium-like states and the bottom meson loops in the heavy quark spin flip transitions . Depending on the constructive or destructive interferences between the -exchange and the bottom meson loops mechanisms, we predict two possible branching ratios for each process: BR or , and or . The contribution of the bottom meson loops is found to be considerably larger than that of the -exchange in the transitions, while its decay rates are not comparable to those of heavy quark spin conserved processes. We also predict the contribution of the charm meson loops in the branch fractions of .

Heavy quark spin multiplet structure of Pc-like pentaquarks as a P-wave hadronic molecular state

Abstract We study the heavy quark spin (HQS) multiplet structure of P-wave $Q\bar{Q}qqq$-type pentaquarks treated as molecules of a heavy meson and a heavy baryon. We define the light-cloud spin (LCS) basis decomposing the meson–baryon spin wave function into LCS and HQS parts. Introducing the LCS basis, we find HQS multiplets classified by the LCS: five HQS singlets, two HQS doublets, and three HQS triplets. We construct the one-pion exchange potential respecting the heavy quark spin and chiral symmetries to demonstrate which HQS multiplets are realized as a bound state. By solving the coupled channel Schrödinger equations, we study the heavy meson–baryon systems with $I=1/2$ and $J^P=(1/2^+, 3/2^+, 5/2^+, 7/2^+)$. The bound states which have the same LCS structure are degenerate at the heavy quark limit, and the degeneracy is resolved for finite mass. This HQS multiplet structure will be measured in future experiments.

Prediction of hidden charm strange molecular baryon states with heavy quark spin symmetry

We have studied the meson-baryon S−wave interaction in the isoscalar hidden-charm strange sector with the coupled-channels, ηcΛ, J/ψΛ, D¯Ξc, D¯sΛc, D¯Ξc′, D¯⁎Ξc, D¯s⁎Λc, D¯⁎Ξc′, D¯⁎Ξc⁎ in JP=1/2−, J/ψΛ, D¯⁎Ξc, D¯s⁎Λc, D¯⁎Ξc′, D¯Ξc⁎, D¯⁎Ξc⁎ in 3/2− and D¯⁎Ξc⁎ in 5/2−. We impose constraints of heavy quark spin symmetry in the interaction and obtain the non vanishing matrix elements from an extension of the local hidden gauge approach to the charm sector. The ultraviolet divergences are renormalized using the same meson-baryon-loops regulator previously employed in the non-strange hidden charm sector, where a good reproduction of the properties of the newly discovered pentaquark states is obtained. We obtain five states of 1/2−, four of 3/2− and one of 5/2−, which could be compared in the near future with forthcoming LHCb experiments. The 5/2−, three of the 3/2− and another three of the 1/2− resonances are originated from isoscalar D¯(⁎)Ξc′ and D¯(⁎)Ξc⁎ interactions. They should be located just few MeV below the corresponding thresholds (4446, 4513, 4588 and 4655 MeV), and would be SU(3)-siblings of the isospin 1/2 D¯(⁎)Σc(⁎) quasi-bound states previously found, and that provided a robust theoretical description of the Pc(4440), Pc(4457) and Pc(4312) LHCb exotic states. The another two 1/2− and 3/2− states obtained in this work are result of the D¯(⁎)Ξc−Ds(⁎)Λc coupled-channels isoscalar interaction, are significantly broader than the others, with widths of the order of 15 MeV, being D¯s(⁎)Λc the dominant decay channel.

Strange hadrocharmonium

It has been recently suggested that the charged charmoniumlike resonances Zc(4100) and Zc(4200) are two states of hadrocharmonium, related by the charm quark spin symmetry in the same way as the lowest charmonium states ηc and J/ψ. It is pointed out here that in this picture one might expect existence of their somewhat heavier strange counterparts, Zcs, decaying to ηcK and J/ψK. Some expected properties of such charmoniumlike strange resonances are discussed that set benchmarks for their search in the decays of the strange Bs mesons.

Decays of Pc into J/ψN and ηcN with heavy quark spin symmetry

We investigate the consequences of heavy quark spin symmetry (HQSS) on hidden-charm pentaquark $P_c$ states. As has been proposed before, assuming the $P_c(4440)$ and the $P_c(4457)$ as $S$-wave $\bar{D}^*\Sigma_c$ molecules, seven hadronic molecular states composed of $\bar{D}\Sigma_c$, $\bar{D}\Sigma_c^*$, $\bar{D}^*\Sigma_c$, and $\bar{D}^*\Sigma_c^*$ can be obtained, with the $\bar{D}\Sigma_c$ molecule corresponding to the $P_c(4312)$. These seven states can decay into $J/\psi N$ and $\eta_c N$, and we use HQSS to predict ratios of partial widths of the $S$-wave decays. For the decays into $J/\psi N$, it is found that among all six $P_c$ molecules with spin $1/2$ or $3/2$, at least four states decay much more easily into the $J/\psi N$ than the $P_c(4312)$, and two of them couple dominantly to the $\bar D^*\Sigma_c^*$. While no significant peak around the $\bar{D}^*\Sigma_c^*$ threshold is found in the $J/\psi p$ distribution, these higher $P_c$ states either are produced with lower rates or some special production mechanism for the observed $P_c$ states might play an important role, such as an intricate interplay between the production of pentaquarks and triangle singularities.

Quark polarimetry with a recursive fragmentation model including the spin degree of freedom

Several estimators of the initial transverse polarization of a quark fragmenting into a jet are proposed and compared using Monte Carlo simulations. These are based on the simplified version of a recursive model [A. Kerbizi et al, Phys. Rev. D97, 074010 (2018)] which includes the quark spin degree of freedom.

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.

Strong decays of the latest LHCb pentaquark candidates in hadronic molecule pictures

We investigate the observed pentaquark candidates $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ from the latest LHCb measurement, as well as four possible spin partners in the $\bar{D}^{(*)}\Sigma_c^*$ system predicted from the heavy quark spin symmetry with the hadronic molecule scenarios. Similar to the previous calculation on $P_c(4380)$ and $P_c(4450)$, the partial widths of all the allowed decay channels for these $P_c$ states are estimated with the effective Lagrangian method. The cutoff dependence of our numerical results are also presented. Comparing with the experimental widths, our results show that $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ can be described well with the spin-parity-$1/2^-$-$\bar{D}\Sigma_c$, $1/2^-$-$\bar{D}^*\Sigma_c$ and $3/2^-$-$\bar{D}^*\Sigma_c$ molecule pictures, respectively.

Some decay properties of hidden-charm pentaquarks as baryon-meson molecules

It is pointed out that the previously suggested interpretation of the hidden-charm pentaquarks $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ as molecular bound states of $\Sigma_c \bar D$ and $\Sigma_c \bar D^*$ baryon-meson pairs gives rise to specific relations for their decays. In particular, the heavy quark spin symmetry predicts ratios of rates of decays of each of the molecules to $J/\psi p$ and to $\eta_c p$ as well as of the decays to $\Lambda_c \bar D$ and to $\Lambda_c \bar D^*$. Experimental studies of these relations would thus provide an indicative probe of the molecular structure.

Hidden charm pentaquark states and ΣcD¯(*) interaction in chiral perturbation theory

In this work, we employ the heavy hadron chiral perturbation theory (HHChPT) to calculate the $\Sigma_c\bar{D}^{(*)}$ potentials to the next-to-leading order. The contact, the one-pion exchange and the two-pion exchange interactions are included. Besides, the mass splittings between the heavy quark spin symmetry (HQSS) multiplets are kept in calculations. Our result shows that neglecting the heavy quark symmetry (HQS) violation effect may be misleading to predict the potentials between the charmed hadrons. We perform numerical analysis with three scenarios. In the first scenario, we relate the low-energy constants (LECs) in the contact terms of $\Sigma_c\bar{D}^{(*)}$ to those of nucleon systems, and reproduce the $P_c(4312)$ and $P_c(4440)$ as loosely bound states. In the second scenario, we vary the unknown LECs and find a small parameter region in which $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ can coexist as molecular states. In the third scenario, we include the coupled-channel effect on the basis of scenario II, and notice that the three $P_c$ states can be reproduced as molecular states simultaneously in a large region of parameters. Our analytical results can be used for the chiral extrapolations in lattice QCD. With the lattice QCD results in the future as inputs, the identification of the $P_c$ states and predictions for other systems would be more reliable.

Heavy quark spin symmetric molecular states from D¯(*)Σc(*) and other coupled channels in the light of the recent LHCb pentaquarks

We consider the ${\bar D}^{(*)}\Sigma_c^{(*)}$ states, together with $J/\psi N$ and other coupled channels, and take an interaction consistent with heavy quark spin symmetry, with the dynamical input obtained from an extension of the local hidden gauge approach. By fitting only one parameter to the recent three pentaquark states reported by the LHCb collaboration, we can reproduce the three of them in base to the mass and the width, providing for them the quantum numbers and approximate molecular structure as $1/2^-$ $\bar{D} \Sigma_c$, $1/2^-$ $\bar{D}^* \Sigma_c$, and $3/2^-$ $\bar{D}^* \Sigma_c$, and isospin $I=1/2$. We find another state around 4374 MeV, of $3/2^-$ $\bar{D} \Sigma_c^*$ structure, for which indications appear in the experimental spectrum. Two other near degenerate states of $1/2^-$ $\bar{D}^* \Sigma_c^*$ and $3/2^-$ $\bar{D}^* \Sigma_c^*$ nature are also found around 4520 MeV, which although less clear, are not incompatible with the observed spectrum. In addition, a $5/2^-$ $\bar D^* \Sigma_c^*$ state at the same energy appears, which however does not couple to $J/\psi p$ in $S-$wave, and hence it is not expected to show up in the LHCb experiment.