Effective nuclear forces in the quark model with delta and hidden-color channel coupling

Adiabatic potentials are calculated in a six-quark cluster model corresponding to having NN, ΔΔ and CC (hidden color) channel coupling. Color-dependent quark interactions are used that yield the N and Δ positive- and negative-parity resonances up to 2 GeV. Channel coupling is found to be large (especially with the CC state) and yields an effective NN potential having none of the characteristics of phenomenological potentials extracted from phase shifts.     

Nucleon-nucleon potentials including πNΔ coupling effects

We show that in the nonrelativistic limit the two-pion exchange contribution to the nucleon-nucleon (NN) interaction can be well approximated by the twice iterated static pion-exchange potentials that couple the NN channel with the NΔ (1236 resonance) and ΔΔ channels. A phenomenological short (ω-meson) range potential is added to the pion-exchange potentials to study the NN phase shifts and the deuteron properties. The S- and P- state phase shifts can be well explained in this model with a very reasonable short-range interaction. The Δ-percentage in the deuteron is found to be ≈ 0.6%. Probably because of the nonrelativistic approximations, the D-state phase shifts at E_lab > 100 MeV are not too well reproduced.     

不带奇异数的双重子态（英文）

在手征SU（3） 夸克模型下应用共振群方法讨论了三个非奇异的双重子态的性质。计算中的模型参数取自我们以前的工作,拟合核子-核子相互作用散射相移确定下来的。首先,研究了氘核的性质,这是非常重要的,因为氘核是多年来实验上唯一发现的双重子态。氘核属于核子-核子系统,它是自旋为S =1 和同位旋为T =0 的双重子态。我们计算了氘核的结合能、散射长度以及氘核的相对运动波函数,结果表明手征SU（3） 夸克模型可以合理描述氘核的性质并且发现张量力对形成松散束缚态的氘核是重要的。然后,给出了S = 3 和T =0 的ΔΔ双重子态的理论预言结果,这里考虑了分波耦合和隐色道耦合效应,计算了结合能和均方根半径。结果表明,隐色道耦合效应比分波耦合效应大,也就是说隐色道耦合效应在形成（ΔΔ）_ST=30 双重子态中是重要的。我们的理论预言结果在几十个MeV 左右,低于ΔΔ道的阈值但是高于NΔπ的阈值. 出乎意料地,我们的预言结果很接近最近2014 年WASA的实验结果。接着,给出了对S = 0 和T =3 的ΔΔ双重子态性质的最新研究结果,这里在以前的单道计算基础上考虑了隐色道耦合效应。结果表明,隐色道耦合对（ΔΔ）ST=03的结合能也有较大的影响。但是,和（ΔΔ）_ST=30 一样,它的质量低于ΔΔ道的阈值但是高于NΔπ的阈值。最后,对S = 3 以及S = 0 两个不同ΔΔ自旋态,详细比较了两者结构之间的差异。结果表明,σ'介子交换和OGE 交换对自旋S = 0 和S = 1 态提供的吸引作用分别是主要的,从而导致耦合道计算中系统的结合能变大。In the present work we discuss three dibaryons without strangeness in the chiral SU(3) quark model by solving the resonating group method (RGM) equation. In the calculation, the model parameters are taken from our previous work in which the nucleon-nucleon (NN) scattering phase shifts are fitted quite well. Firstly, the structure of deuteron is discussed, which is very important since it is the first dibaryon confirmed by experiment in the past many years. Deuteron belongs to NN system with spin S =1 and isospin T =0, the binding energy, scattering length and the relative wave functions of deuteron are discussed. The results show that the chiral SU(3) quark model describes the properties of deuteron quite well and tensor interaction is important in forming the deuteron loosely bound. Secondly, the predicted results of ΔΔ dibaryon with S =3 and T =0 are shown, the resultant binding energy and size of root-mean-square (RMS) of six quarks are calculated by including the L coupling and hidden color channel (CC) coupling. The results show that the CC coupling effect is much larger than the L mixing effect, which means that CC coupling plays an important role in forming the spin S =3 ΔΔ dibayon state. Our predicted binding energy is several tens MeV, it is lower than the threshold of the ΔΔ channel and higher than the mass of NΔπ. Unexpectedly, our predicted mass is quite close to the recent confirmation by WASA experiments in 2014. Thirdly, we present our new results of ΔΔ dibaryon with S = 0 and T =3, obtained recently by extending the single-channel calculation to including the CC coupling. It is seen that the CC coupling also has a relatively large effect on (ΔΔ)ST=03 state. However, its mass is still lower than the threshold of the ΔΔ channel and higher than the mass of NΔπ, similar as that of (ΔΔ)_ST=30 state. Finally, we further make some comparisons between S = 3 and S = 0 ΔΔ states to show the difference of the two dibaryons. The results show that the attractive interactions from σ' meson and OGE exchanges are dominantly important for S =0 and S =3 states, respectively, so their binding energies all become larger in coupled-channel calculation.     

An Extended Chiral SU(3) Quark Model

The chiral SU(3) quark model is extended by including the vector meson exchanges to describe the short range interactions. The phase shifts of NN scattering are studied in this model. Compared with the results of the chiral SU(3) quark model in which only the pseudo-scalar and scalar chiralfields are considered, the phase shifts of 1 So wave are obviously improved.     

The Effective Degree of Freedom of Low Energy QCD

The adiabatic effective baryon-baryou interactions and dibaryon candidates are studied systematically with three constituent quark models based on different effective degrees of freedom:Glozman-Riska-Brown Goldstone boson exchange model based on constituent quark and Goldstone boson coupling;Fujiwara model based on constituent quark gluon coupling and Nijmegen one-boson exchange;QDCSM based on constituent quark and gluon coupling with quark delocalization and color screening.We find that the three models predicted the similar effective baryon-baryon interactions for roughly two thirds among the 64 states consisted of octet and decuplet baryons.The differences among three models and their separate characteristics are also studied.     

NN tensor and LS potentials in a quark model with quark-antiquark excitations

A more detailed study is made of the NN interaction in a quark model in which the (qq̄) excitations inherent in the quark-gluon interaction are explicitly incorporated into the model space. A unified treatment for all types of exchange terms of the (3q)-(3q) to (3q)-(3q)(qq̄) coupling kernels is used to calculate the space parts of the full coupling kernels and their Wigner transforms in complete analytic form. The present investigation focuses on the noncentral parts of the NN interaction. The tensor force gains almost its full strength from coupling kernels of Nπ and Nρ type. If the Nπ contribution is adjusted to fit the experimental pion-nucleon coupling constant the predicted strength of the full tensor force is in reasonable agreement with that of conventional OBEP's over the range in which the tensor force can act. The LS force gains contributions from both the pure (3q)-(3q) and the coupling kernels, but the dominant contributions (about 60–65% of the triplet-odd LS potential in the 0.7–1.0 fm range), come from the coupling kernels and particularly from the Nω and Nρ components. The triplet-odd LS potential derived from the full quark-exchange kernel is in remarkably good agreement with the OBEP LS potential over the significant range. Both the tensor and LS potentials are approximated surprisingly well over their full range by the simple (qq̄) exchange terms of our model. The ³P RGM phase shifts are calculated to show that both tensor and LS forces of our quark model are in good agreement with the experimental facts.     

The N~* physics program at Jefferson Lab

Recent measurements of nucleon resonance transition form factors with CLAS at Jefferson Lab are discussed. The new data confirm the assertion of the symmetric constituent quark model of the Roper as the first radial excitation of the nucleon. The data on high Q~2 nπ~+ production better constrain the branching ratios β_(Nπ) and β_(Nη). For the first time, the longitudinal transition amplitude to the S_(11)(1535) was extracted from the nπ~+ data. Also, new results on the transition amplitudes for the D_(13)(1520) resonance are presented showing a rapid transition from helicity 3/2 dominance seen at the real photon point to helicty 1/2 dominance at higher Q~2. I also discuss the status of the search for new excited nucleon states.     

A study of six quark cluster states in chiral SU(3) quark model

The energies of the (0S)⁶ six quark cluster states are calculated in the chiral SU(3) quark model. The results show that some states with high strangeness have more attraction from the chiral SU(3) coupling, and this feature is interesting in discussing if there exists some new narrow width six quark states. Further, we did a RGM calculation to study some multi-strangeness dibaryon states. We found that ΩΩ dibaryon is a deeply bound state and ΞΩ dibaryon is slightly bound.     

核力夸克模型中N△道耦合效应的研究

在核力的夸克-SU(3)手征场耦合模型基础上研究了N△道耦合效应对NN散射相移的影响. 结果表明N△的5D0分波与NN道的1S0分波间的耦合效应较大,NN的D､F分波与N△道之间的耦合效应较小.     

Comments on np elastic scattering, 142–800 MeV

Important new data of McNaughton et al. on np Wolfenstein parameters are added to NN phase-shift analysis. At 800 MeV, there is a dramatic improvement and one can see with confidence which way phase shifts are heading from 500 to 800 MeV. Dispersive effects in ³D₁ and ³G₃ herald the onset of I = 0 inelasticity. Phase shifts account naturally for the energy dependence of Δσ_L and Δσ_T for np scattering and do not support the claim of Beddo et al. for an I = 0 dibaryon resonance near 733 MeV.     

Meson Cloud Effect on △(1232) Resonance Transition Properties with a Relativistic Quark Model Approach

Based on a relativistic quark model approach, the transition properties of the first nucleon resonance △(1232), and the coupling constants gπNN, g△πN are investigated. Tvo different vays to remove the center of mass motion are considered. The results of the relativistic approaches with and without center ofmass correction are compared with those of nonrelativistic constituent quark model. Moreover, pion meson cloud effect on these calculated observables is explicitly addressed. Better results are obtained by taking the pion meson cloud into account.     

Pionic decay of a possible dibaryon d’ and quark models of πB and πd’ couplings

The pionic decay of a possible dibaryon, d’ → πNN, is studied in the model assuming the production of ³ P ₀ quark-antiquark pairs and in other models of effective quark-pion coupling. The vertex constants and the form factors for pion-baryon and pion-dibaryon couplings are calculated. The effect of the internal pion structure on decay widths is investigated. It is shown that the quark structure of the nucleon-nucleon wave function in the overlap region plays an important role in dibaryon decays, and known models of nucleon-nucleon interaction are analyzed with allowance for this circumstance. The decay width of a dibaryon is estimated as a function of its effective mass in nuclear matter.     

Tensor Interaction Effect in Dibaryon

The gluon and Goldstone boson induced tensor interaction effect on the dibaryon mass and the D-wave decay width has been studied in the quark delocalization, color screening model. The effective S-D wave transition interactions induced by gluon and Goldstone boson exchanges decrease quickly as the increasing of the channel strangeness. The K and η meson tensor contribution is negligible in this model. No six-quark state in the light flavor world can become a bound one by the help of these tensor interactions except the deuteron. The partial D-wave decay width of IJ^p=\frac{1}{2}2⁺ NΩ state to spin 0, 1 ΛΞ final state is 20.7 keV and 63.1 keV respectively. It is a very narrow dibaryon resonance and might be detected in the relativistic heavy ion reaction by the existing RHIC detectors through the reconstruction of the ΛΞ vertex mass and the future COMPAS detector at CERN and FAIR project in Germany.     

The Structure of Deltaron Dibaryon

We discuss the structure of deltaron dibaryon in the chiral quark model. The energy of deltaron is obtained by considering the coupling of the ΔΔ and CC (hidden color) channels. It is shown that the mass of deltaron is lower than the mass of ΔΔ but higher than the mass of Δ N π.     

NN potential with a six-quark core from the constituent quark model

A mesonic nucleon-nucleon potential from an effective quark interchange mechanism for non-overlapping nucleons is obtained from the constituent quark model. This is supplemented at short range by a phenomenological, non-mesonic potential describing the transition to a six-quark core with a discrete energy spectrum. NN phase shifts and low energy parameters are calculated and compared with data and phase shift analyses. Core parameters are extracted from the fits.     

手征–夸克耦合与双重子结构

运用SU(3)手征夸克模型,系统地研究了H,d*和d＇三个六夸克体系的结构,分析了SU(3)手征场和矢量耦合禁闭势等非微扰效应对三种六夸克态能量的影响.结果发现,SU(2)手征场的耦合,对形成六夸克态是有利的,但是扩大到SU(3)手征对称,则由于这些手征场的“云”,对六夸克系统形成束缚的双重子态起到了限制的作用,矢量耦合禁闭势有利于H的形成,而对d*则相反.     

The deuteron asymptotic D-state as a probe of the nucleon-nucleon force

A critical discussion is given of the various contributions to the asymptotic D/S ratio from the πNN interaction. Particular emphasis is laid on the analysis of contributions from 2π exchange, the dependence on the πNN form factor, and on the πN coupling constant, so as to assess quantitatively the model dependence of the result. From this analysis, significant restrictions are deduced on the shape of the πNN form factor and, in quark bag models, the value of the quark bag radius. The results of previous theoretical approaches for the D/S ratio and quadrupole moment are shown to obey a universal and linear relation, when expressed in reduced units so as to compensate for small differences in effective range and πN coupling constant. The quadrupole moment is also quantitatively analyzed in detail. Its value is proved to be an accurate and almost model-independent consequence of the experimental D/S ratio (apart from relativistic and meson-exchange corrections) in agreement with observations. In the comparison with experiments, a critical survey of the relevant experimental data is given. In particular, a considerably improved value for the quadrupole moment is deduced.     

Quark cluster model and the R-matrix theory treatment of NN scattering

A microscopic quark cluster model has been developed for six-quark states consisting of two s³ quark clusters. The consequences of channel nonorthogonality and existence of Pauliforbidden states are investigated explicitly by solving the eigenvalue problem of the resonating group method (RGM) kernel. Since the RGM kernels needed are all available, the form of the six-quark states given in this paper is very suited to detailed RGM calculations. A rigorous treatment based on the R-matrix theory has been carried out to obtain NN phase shifts. The spin-spin term of the quark-quark interaction favors states of higher color-spin symmetry. This explains the larger change caused by the hidden color states in the ³S₁ phase shifts than in the ¹S₀ phase shifts. Phase shifts calculated with inclusion of the delta and hidden color states are still too repulsive. It is pointed out that there arises a subtle problem in adding the one-boson exchange potential by hand to the RGM equation.