Helicity Amplitudes for Photoproduction of Baryons with J = 1/2 and JP = 3/2+

We derive the separate helicity amplitudes using the partial wave analysis in the process of pseudo-scalar meson photoproduction. For J^P = 3/2⁺, we find the amplitude is model independent. According to parity conservation, the general amplitude in the case of J^P = 1/2^- is obtained. We prove this general amplitude corresponds to the situation of λ= -1 when adopting the circular polarization. Finally, the formulas of scattering amplitudes involving the meson photoproduction with J^P = 3/2⁺ are obtained from the chiral quark model.     

Chiral SU（3） Quark Model Study of Tetraquark States： cnn^-s^-/css^-s^-

The new members of the charm-strange family Dsj^＊（2317）, Dsj（2460）, and Ds（2632）, which have the surprising properties, are challenging the present models. Many theoretical interpretations have been devoted to this issue. Most authors suggest that they are not the conventional cs^- quark model states, but possibly are four-quark states, molecule states, or mixtures of a P-wave cs^- and a four-quark state. In this work, we follow the four-quark-state picture, and study the masses of cnn^-s^-/css^-s^- states （n is u or d quark） in the chiral SU（3） quark model. The numerical results show that the mass of the mixed four-quark state （cnn^-s^-/css^-s^-） with spin parity j^P ： 0^＋ might not be Ds （2632）. At the same time, we also conclude that Dsj^＊（2317） and Dsj（2460） cannot be explained as the pure four-quark state.     

Λc重子谱疑难(英文)

Λ_c+重子家族存在一个疑难,也就是重夸克有效理论预言的轨道角动量为L=2的多重态中JP=3/2+的态在实验上是缺失的,而且已发现的Λ_c（2765）+和Λ_c（2940）+的JP量子数仍然未知。在本工作中,我们使用双夸克图像计算了重子的质量,研究了Λ_c（2765）+和Λ_c（2940）+的可能归类以及仍缺失的具有L=2和JP=3/2+量子数的Λ_c+态,进而指出Λ_c（2880）+的峰结构中实际上已经包含了L=2、JP=3/2+这一缺失态,并建议Λ_c（2765）+和Λ_c（2940）+的量子数应分别为2S（1/2+）和2P（1/2-）。There is a puzzle in the Λ_c+ family, i.e., one member with JP=3/2+ is missing in a L=2 multiplet which the heavy quark effective theory predicts, and JP's of Λ_c(2765)+ and Λ_c(2940)+ are unknown. Using a light diquark picture to calculate baryon masses, we study possible assignments of two Λ_c's with unknown JP and the missing Λ_c+ with 3/2+ for L=2, and we find the most probable possibility that the peak corresponding to Λ_c(2880)+ actually includes a missing member with spin 3/2+ for L=2 and that quantum numbers of Λ_c(2765)+ and Λ_c(2940)+ are 2S(1/2+) and 2P (1/2-), respectively.     

THE CONVERSION OF GLUONS INTO QUARKS AND THE MULTIQUARK STATES

The rate for the conversion of the gluon into a color octet quark pair which subsequently forms a multiquark state with another quark pair or a gluon is discussed. The static potential in a [(QQ)₈(qq)_8,1] state where Q=c,b and q=u, d is studied in the MIT bag model. It is shown that the repulsive Coulomb force between Q and Q is dominant at small QQ separations, which would significantly suppress the QQ wave function at the origin. For the charm quark (Q=c) the ratio of |Ψ(O)|² for the ordinary (QQ)₁ to that for the(QQ)₈ in the [(QQ)₈(qq)_8,1] state is estinated to be 2-5. Therefore the assumption |Ψ₈(O)|²=|Ψ₁(O)|² would lead to an overestimation for the rate of g*→QQ and it is necessary to take the suppression effect of the repulsive Coulomb force into consideration.     

Structures of（ΩΩ）0＋and（[1]Ω）1＋in Extended Chiral SU（3） Quark Model

The structures of (ΩΩ)0 and ([1]Ω)1 are studied in the extended chiral SU(3) quark model in which vector meson exchanges are included. The effect from the vector meson fields is very similar to that from the one-gluon exchange (OGE) interaction. Both in the chiral SU(3) quark model and in the extended chiral SU(3) quark model,di-omega (ΩΩ)0 is always deeply bound, with over one hundred MeV binding energy, and ([1]Ω)1 ‘s binding energy is around 20 MeV. An analysis shows that the quark exchange effect plays a very important role for making di-omega (ΩΩ)0 deeply bound.     

The Ξ~* K and ?η Interaction Within a Chiral Unitary Approach

In this work we study the interaction of the coupled channels ?η and Ξ* ˉK within the chiral unitary approach.The systems under consideration have total isospins 0,strangeness S =-3,and spin 3/2.We study the s wave interaction which implies that the possible resonances generated in the system can have spin-parity JP= 3/2-.The unitary amplitudes in coupled channels develop poles that can be associated with some known baryonic resonances.We find there is a dynamically generated 3/2-? state with mass around 1800 Me V,which is in agreement with the predictions of the five-quark model.     

Glueballs and Instantons in Lattice SU(2) Gauge Theory

The SU(2) glueball masses and the gluonic correlation functions in the J^P = 0⁺,2⁺ and 0^- channels are calculated from the cooled and uncooled gauge configurations. The improved action and the anisotropic lattice are used in this work. The instanton-induced attractive force in the 0⁺ channel and the repulsive force in the 0^- channel are confirmed by the Monte Carlo simulation. There is evidence that the instanton vacuum contribution to the 0⁺ glueball mass is significant.     

HYPERON DECAYS IN THE CNIRAL BAG MODEL

In terms of the chiral bag model and SD(3) Skyrme wave-functions of baruons, we investigate Δ⁺ →Pγ (SU(2)) and Σp⁺ → Pπ⁰ (SU(3) case) hyperon decays. We have found that for Δ⁺ →Pγ the Skyrme contribution is more important whereas in Σp⁺ → Pπ⁰ the quark content transition dominates.     

Production Rate of Ds+Ds- at φ(4030)

By using a generalized relativistic quark pair creation model (QPCM), the hadronic decay processes of φ(4030), assigned as the 3S state of cc, are investigated. The relative rates of φ(4030) → DD, DD^*+DD^*, D^*D^*,and in particular D_s⁺D_s^- are calculated and compared with data. The nodes of the radially excited wavefunctions of charmonium states are found to be significant for these decay processes. Considering the SU(3) suppression factor of ~3 for the s quark pair creation relative to the u and d quarks, we obtain σ(e⁺e^- → φ4(4030) → D_s⁺D_s^-) ~ 0.9 nb.     

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.     

On Possible S-Wave Bound States for an N\bar{N} System Within a Constituent Quark Model

We try to apply a constituent quark model (a variety chiral constituent quark model) and the resonating group approach for the multi-quark problems to compute the effective potential between the N\bar{N} in S-wave (the quarks in the nucleons N and \bar{N}, and the two nucleons relatively as well, are in S wave) so as to see the possibility if there may be a tight bound state of six quarks as indicated by a strong enhancement at threshold of p\bar{p} in J/ψ and B decays. The effective potential which we obtain in terms of the model and approach shows if the experimental enhancement is really caused by a tight S-wave bound state of six quarks, then the quantum number of the bound state is very likely to be I=1, J^PC=0^-+.     

Pion-transfer (n, d) and (d, He) reactions leading to deeply bound pionic atoms

Theoretical studies are given on the (n, d) and (d, ³He) reactions leading to deeply bound pionic atoms in heavy nuclei of configuration [(nl)_π·j_n⁻¹]J. The cross sections for various pionic and neutron-hole configurations in the case of a ²⁰⁸Pb target are calculated at incident energies 300–1000 MeV/u by using the effective number approach and the eikonal approximation for distortion. The effective number with a pion in the 1s or 2p state and a neutron hole in the orbit peaks around the same incident energy (T_n = 600 MeV) as the elementary cross section n+n→d+π⁻, where the momentum transfer matches the angular-momentum transfer of L = 5–7. The DWIA cross section for (n,d) producing a pion in the 1s or 2p orbit at T_n = 600 MeV is found to be around 42 or 75 μb/sr, respectively. At T_n = 350 MeV, where the momentum transfer is small, quasi-substitutional states of configurations and are preferentially populated with (n, d) cross sections of 95 and 190 μb/sr, respectively. The (d, ³He) cross sections are estimated to be an order of magnitude smaller than the (n, d) cross sections. Thus, the (n, d) and (d, ³He) reactions are found to be suited for the production of deeply bound pionic atoms.     

手征夸克模型下udss四夸克态的研究

在手征SU(3)夸克模型和扩展的手征SU(3)夸克模型的框架下, 用变分的方法系统地研究了同位旋为0、1, 自旋宇称为0⁺、1⁺和2⁺的udss四夸克系统6个低组态的能量. 模型的参数取自以前的工作, 它能很好地描述核子-核子散射相移以及核子-超子散射截面. S道相互作用的参数由拟合K介子和K^*介子的质量定出, 并且考虑了具有相同量子数的态之间的态混合效应. 结果表明, 同位旋为0且自旋宇称为1⁺的udss能量低于相应的K^*K^*,的阈能, 且该组态中KK^*的成分相当小, 因此该组态的宽度可能较小, 可视为一个可能的四夸克态的候选者.     

The nature of 0 excitations in Er

Lifetimes of excited 0⁺ states in ¹⁶⁶Er have been measured with the (n,n′γ) reaction. The first and second excited 0⁺ states have no significant collective enhancements of their decays, and their properties are suggestive of pair-type excitations rather than those of a β vibration or phonon excitation built on the γ vibration. The third excited 0⁺ state at 1934 keV has an enhanced decay to the ground state band with B(E2; 0₄⁺ → 2_gsb⁺) = 8.8 ± 0.9 W.u., consistent with that expected for a β vibration.     

Analysis of X(5568) as Scalar Tetraquark State in Diquark-Antidiquark Model with QCD Sum Rules

In this article, we take the X(5568) as the diquark-antidiquark type tetraquark state with the spin-parity J^P=0⁺, construct the scalar-diquark-scalar-antidiquark type current, carry out the operator product expansion up to the vacuum condensates of dimension-10, and study the mass and pole residue in details with the QCD sum rules. We obtain the value M_X=(5.57±0.12) GeV, which is consistent with the experimental data. The present prediction favors assigning the X(5568) to be the scalar tetraquark state.     

Generalized vector dominance and the pion form factor

We have calculated the pion form factor using the bound state Bethe-Salpeter amplitudes and the quark form factor of a relativistic quark model. We obtain a generalized vector dominance structure and an asymptotic behaviour in the space-like region F_π(Q)² −0.33 GeV²/Q².     

The Three-Pion Decays of the a1(1260)

We investigate the decay of a₁⁺ (1260)→π⁺π⁺π^- with the assumption that the a₁(1260) is dynamically generated from the coupled channel ρπ and KK^* interactions. In addition to the tree level diagrams that proceed via a₁⁺ (1260)→ρ⁰π⁺→π⁺π⁺π^-, we take into account also the final state interactions of ππ→ππ and KK→ππ. We calculate the invariant π⁺π^- mass distribution and also the total decay width of a₁⁺ (1260)→π⁺π⁺π^- as a function of the mass of a₁(1260). The calculated total decay width of a₁(1260) is significantly different from other model calculations and tied to the dynamical nature of the a₁(1260) resonance. The future experimental observations could test of model calculations and would provide vary valuable information on the relevance of the ρπ component in the a₁(1260) wave function.     

icMRCI+Q理论研究CF离子12个-S态和23个?态的光谱性质

采用考虑Davidson修正的内收缩多参考组态相互作用(icMRCI+Q)方法结合相关一致基组aug-ccpV5Z和aug-cc-pV6Z计算了CF~+离子第一离解极限C~+(~2p_u)+F(~2P_u)对应的12个∧-S态(X~l∑~+,a~3∏,1~3∑~+,1~3Δ,1~1∑~-,1~1∑~-,1~3∑~-,2~1∑~+,1~1∏,2~3∏,2~1∏和2~3∑~+)所产生的23个Ω态的势能曲线.计算中考虑了旋轨耦合效应、核价相关和标量相对论修正以及将参考能和相关能分别外推至完全基组极限.基于得到的势能曲线,获得了束缚和准束缚的9个∧-S态和16个Ω态的光谱常数,并且X~1∑~+,a~3∏~(势阱一)∧-S态的光谱常数与已有的实验结果非常符合.此外,计算了CF自由基X~2∏态到CF~+离子束缚和准束缚的9个∧-S态的垂直电离势和绝热电离势,并且CF~+(X~1∑~+)←CF(X~2∏)和CF~+(a~3∏(势阱一))←CF(X~2∏)的垂直电离势和绝热电离势与相应的实验结果也非常符合.由a~3∏,1~1∏态和其他激发∧-S态势能曲线的交叉现象,借助于计算的旋轨耦合矩阵元,分析了a~3∏~(势阱一),1~1∏~(势阱一)和2~1∑~+态的预解离机理.计算的23个Ω态离解极限处的相对能量与实验结果十分吻合.最后计算了(2)0+~(势阱一)(v'=0-5),(1)1~(势阱一)(v'=0-5)和(2)1~(势阱一)(v'=0)到X0~+态跃迁的Franck-Condon因子和辐射寿命.     

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.