正反重强子对构成的强子分子态能谱（英文）

近二十年来,世界上众多高能物理实验发现了大量超出传统夸克模型的共振结构。为了理解这些性质奇特的共振结构,科学家们提出了很多方法和模型。其中,因为实验上发现的这些奇特态大多处在一对强子阈值附近,强子分子态的观点得到了很多关注。本文我们将以粲–反粲强子对为例来探究哪些系统可以形成分子态,进而给出粲–反粲强子分子态的能谱。我们考虑了所有由S波粲介子、粲重子以及窄的P波粲介子构成的粲–反粲强子对。我们假定它们之间的相互作用由介子交换主导,在最低阶近似下可简化为常数。通过求解常数相互作用的Bethe–Salpeter方程,我们可以找到振幅的极点进而确定该系统分子态的质量。最终我们发现,那些通过轻矢量介子交换在阈值附近产生吸引力的系统,会存在一个靠近阈值的极点。不同的系统,由于其相互作用强度不同,极点可能会处于能量复平面的第一黎曼面或者第二黎曼面,分别对应于束缚态或者虚态。我们总共发现了229个强子分子态。很多实验上发现的那些位于粲–反粲强子对阈值附近的共振结构可以很好地与我们的结果吻合。另外,我们需要强调所预言的一个ΛcˉΛc分子态,这个态可以很好地解释北京正负电子谱仪(BESIII)上测量的数据。     

阈效应和奇特强子态信号

综述了量子色动力学奇特强子态研究中的一些热点问题，特别强调了有效理论研究强子分子态可以合理考虑阈效应和“三角奇异性”对近阈奇特强子态性质的重要影响，综合分析这些可能的机制可以帮助我们更好地理解强子谱。     

J/ψ强子衰变和1－+奇特态

本文从推广的矩分析出发,给出了在J/ψ强子衰变过程中区分1^－+奇特态和1⁺⁺普通介子的若干关系式.     

HERMES五夸克强子态Θ+实验探索

一个新的强子态的实验证据在2?7.6GeV正电子轰击氘靶产生的虚光子产物中被发现.HERMES通过分析衰变道K0sp→π+π–p,在K0sp不变质量谱上质量1528±2.6(stat.)±2.1(sys.)MeV处观察到共振峰.该共振峰可以被解释为理论预言的五夸克强子态Θ+(uudds).而K+p不变质量谱上未能观察到共振预示Θ+很可能是同位旋单态.     

三角奇点与XYZ类粲偶素结构

对强子谱的研究有助于加深量子色动力学中色禁闭现象的理解。强子谱中存在诸多疑难问题，特别是2003年以来各高能物理实验上发现了很多难以理解的新的强子共振结构，其中大量是在重夸克偶素质量区间发现的，它们被统称为$XYZ$结构。强子共振态对应于$S$矩阵的极点。除此之外，$S$矩阵还具有其它类型的奇点，比如由于三个中间态粒子同时在 壳导致的三角奇点。本文中，我们将讨论三角奇点在$XYZ$物理中的实现，注重于构造可以用来分析 其对$e^+e^-\to\psi\pi^+\pi^-$反应的$\psi\pi$不变质量谱中的带电$Z_c$结构的影响的振幅。     

新的粲素粒子

<正>两个粒子物理实验室的物理学家们独立地发现了一种新的神秘强子的证据。这种名为Zc(3900)的粒子,好像是一种"带电的粲素",是由以前所未见的一种方式组合起来的夸克组成的。对Zc(3900)粒子的进一步研究可能提供关于将夸克束缚在强子内的强力的信息。粲素是重介子,含有一个粲夸克和一个反粲夸克。由于是复合粒子,因而可以处于几种不同的能态。其中最著名的就是其第一激发态,称为J/Ψ粒     

强和弱Y-Y相互作用下的奇异强子物质

把修正的夸克-介子耦合模型推广到包含奇异性的情形， 并用来研究奇异强子物质的状态方程. 从最新的6ΛΛHe双超核的实验导出的弱Λ Λ相互作用和过去采用的强Λ Λ相互作用同时被用于计算. 比较发现， 具有强Λ-Λ相互作用的系统束缚得比正常核物质要紧， 而具有弱Λ Λ相互作用的系统则比正常核物质束缚得要松得多. 无论强还是弱相互作用情况， 为了合适地描述修正的夸克 介子耦合模型中超子-超子（Y Y）相互作用， 必须引进σ*和介子. A modified quark meson coupling (MQMC) model is extended to include Λ hyperons and Ξ hyperons. The extended model is then used to study the equation of state (EOS) for strange hadronic matter. A weak Λ Λ interaction deduced from recent observation of 6ΛΛHe double hypernucleus is adopted in the calculation. The resultant EOS is compared with that deduced from a strong Λ Λ interaction. It is found that while the system with the strong ΛΛ interaction is more deeply bound than ordinary nuclear matter due to the opening of new degrees of freedom， the system with the weak Λ Λ interaction is rather loosely bound compared to the later. It is necessary to introduce the strange mesons σ*and in the MQMC model to describe properly the interaction between the hyperons in either strong or weak ΛΛ interaction case.     

发现ZC（3900）--一个带电类粲偶素共振结构*

北京谱仪(BESⅢ)实验和Belle实验利用两种不同的方法对e+e-→p+p-J/y过程进行了研究。在p±J/y系统中,同时观测到了一个新的带电类粲偶素结构--ZC(3900)。ZC(3900)耦合到粲偶素末态,因此其内部夸克组分应该含有正反粲夸克;同时它还带有电荷,故不可能仅由正反粲夸克组成。ZC(3900)共振态中最少含有4个夸克,极有可能是一个奇特态强子。     

强子衰变对高能反应末态超子极化的影响

在分析不同情形超子衰变的基础上, 给出超子衰变对超子产生率和末态超子极化的贡献的一般计算公式. 用Monte-Carlo数值计算研究强子衰变对高能反应末态超子极化的影响,结果发现, 强子衰变对Λ超子的贡献很大这一结论具有普遍性, 与模型无关; 不同模型给出的单极化pp碰撞产生的大横动量Λ超子极化的差别, 很可能相当大一部分来源于强子衰变. 考虑到衰变对极化贡献的计算中有较大不确定性, 检验不同模型, 最好看Σ^±,Ξ⁰,Ξ^－的极化.     

重夸克偶素的强子跃迁理论

我们知道宏观物体是由分子、原子组成的.原子是由电子和原子核组成的.原子核又是由原子和中子组成的.人们对物质徽观结构和微观运动基本规律的不断深入的研究,推动着物理学不断向前发展.近代粒子物理(又称高能物理)的研究,发现质子、中子和与它们相似的超子等(统称为重子)以及与它们有强相互作用的介子(介子和重子统称为强子)还有更深一层的内部结构.它们是由一种称为夸克的更基本的粒子所组成的.已经知道的夸克有以下几种: u c t(所带电荷为质子电荷的2/3), d s b(所带电荷为质子电荷的-1/3),其中u,d,s,b等夸克的存在已有明确的实验根据,t…     

Study of charm production in Z decays

The production rates of , , , , , and in decays are measured using the LEP I data sample recorded by the ALEPH detector. The fractional energy spectrum of the is well described as the sum of three contributions: charm hadronisation, b hadron decays and gluon splitting into a pair of heavy quarks. The probability for a c quark to hadronise into a is found to be . The average fraction of the beam energy carried by mesons in events is measured to be The energy and the hemisphere mass imbalance distributions are simultaneously used to measure the fraction of hadronic Z decays in which a gluon splits to a pair: The ratio of the Vector/(Vector+Pseudoscalar) production rates in charmed mesons is found to be . The fractional decay width of the Z into pairs is determined from the sum of the production rates for various weakly decaying charmed states to be Received: 21 September 1999 / Published online: 8 June 2000     

D and D_s in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted ma...     

Perfect DD~* Molecular Prediction Matching the T_(cc) Observation at LHCb

In 2012,we investigated the possible molecular states composed of two charmed mesons [Phys.Rev.D 88(2013)114008;2012 arXiv:1211.5007 [hep-ph]].The D~*D system with the quantum numbers of I(J~P)=0(1~+) was found to be a good candidate of the loosely bound molecular state.This state is very close to the D~* D threshold with a binding energy around 0.47 MeV.This prediction was confirmed by the new LHCb observation of T_(cc)~+ [see Franz Muheim's talk at the European Physical Society conference on high energy physics 20211.     

OPE, charm-quark mass, and decay constants of D and Ds mesons from QCD sum rules

We present a sum-rule extraction of the decay constants of the charmed mesons D and Ds from the two-point correlator of pseudoscalar currents. First, we compare the perturbative expansion for the correlator and the decay constant performed in terms of the pole and the running MSˉ masses of the charm quark. The perturbative expansion in terms of the pole mass shows no signs of convergence whereas reorganizing this very expansion in terms of the MSˉ mass leads to a distinct hierarchy of the perturbative expansion. Furthermore, the decay constants extracted from the pole-mass correlator turn out to be considerably smaller than those obtained by means of the MSˉ-mass correlator. Second, making use of the OPE in terms of the MSˉ mass, we determine the decay constants of both D and Ds mesons with an emphasis on the uncertainties in these quantities related both to the input QCD parameters and to the limited accuracy of the method of sum rules.     

D and D_s in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted masses of the 1(13D1) and the 3(13D3) Ds agree well with those of recently observed Ds1(2700)± and DsJ(2860), respectively.     

A new hadron spectroscopy

QCD-motivated models for hadrons predict an assortment of “exotic” hadrons that have structures that are more complex than the quark-antiquark mesons and three-quark baryons of the original quark-parton model. These include pentaquark baryons, the six-quark H-dibaryon, and tetraquark, hybrid and glueball mesons. Despite extensive experimental searches, no unambiguous candidates for any of these exotic configurations have been identified. On the other hand, a number of meson states, one that seems to be a proton-antiproton bound state, and others that contain either charmed-anticharmed quark pairs or bottom-antibottom quark pairs, have been recently discovered that neither fit into the quark-antiquark meson picture nor match the expected properties of the QCD-inspired exotics. Here I briefly review results from a recent search for the H-dibaryon, and discuss some properties of the newly discovered states -the proton-antiproton state and the so-called XY Z mesons- and compare them with expectations for conventional quark-antiquark mesons and the predicted QCD-exotic states.     

How much charm can \bar PANDA produce?

We consider the production of charmed baryons and mesons in the proton-antiproton binary reactions at the energies of the future $\bar P$ ANDA experiment. To describe these processes in terms of hadronic interaction models, one needs strong couplings of the initial nucleons with the intermediate and final charmed hadrons. Similar couplings enter the models of binary reactions with strange hadrons. For both charmed and strange hadrons we employ the strong couplings and their ratios calculated from QCD light-cone sum rules. In this method finite masses of c and s quarks are taken into account. Employing the Kaidalov??s quark-gluon string model with Regge poles and adjusting the normalization of the amplitudes in this model to the calculated strong couplings, we estimate the production cross-section of charmed hadrons. For $p\bar p \to \Lambda _c \bar \Lambda _c$ it can reach several tens of nb at p _lab = 15 GeV, whereas the cross-sections of ?? _c and D pair production are predicted to be smaller.     

Gluon bremsstrahlung production of heavy particles in neutrino and antineutrino scattering

Weak charged current production of charmed quark pairs is studied in the framework of the QCD inspired parton model. The magnitude of the cross section strongly depends on the charmed quark pair production threshold, above which the gluons are assumed to decay into either charmed particle pairs of hidden charmonium states. The normalized distributions are rather insensitive to the choice of this threshold value and the angular distribution of J/gy particles will show significant azimuthal asymmetry about the current-target axis. The sign of the asymmetry cannot be mimicked by the parton primordial transverse momentum effects and thus the process can serve a clean test of the gluon bremsstrahlung mechanism.     

Charmed exotics in heavy ion collisions

Based on the color–spin interaction in diquarks, we argue that charmed multiquark hadrons are likely to exist. Because of the appreciable number of charm quarks produced in central nucleus–nucleus collisions at ultrarelativistic energies, the production of charmed multiquark hadrons is expected to be enhanced in these collisions. Using both the quark coalescence model and the statistical hadronization model, we estimate the yield of charmed tetraquark mesons, T_cc, and pentaquark baryons, Θ_cs, in heavy ion collisions at RHIC and LHC. We further discuss the decay modes of these charmed exotic hadrons in order to facilitate their detections in experiments. PACS 25.75.Dw; 14.20.Lq; 14.40.Lb