An explanation for deviations from the quark number scaling of elliptic flows in low pT region

We carry out a systematic study of the different contributions to the deviations of the elliptic flows from the quark number scaling in high energy heavy ion collision in a quark combination model.The effects that we considered are:the resonance decay,the flavor dependence of the quark elliptic flow and the combination of quarks/antiquarks with slightly different transverse momenta.Our results show that the deviations observed in experiments can be well reproduced within the combination framework if all the three effects are considered. We make a detailed analysis of the different contributions using a Monte-Carlo program and suggest measuring the quark number scaling in intermediate pT range more precisely.     

An explanation for deviations from the quark number scaling of elliptic flows in low PT region

We carry out a systematic study of the different contributions to the deviations of the elliptic flows from the quark number scaling in high energy heavy ion collision in a quark combination model.The effects that we considered are:the resonance decay,the flavor dependence of the quark elliptic flow and the combination of quarks/antiquarks with slightly different transverse momenta.Our results show that the deviations observed in experiments can be well reproduced within the combination framework if all the three effects are considered. We make a detailed analysis of the different contributions using a Monte-Carlo program and suggest measuring the quark number scaling in intermediate P_T range more precisely.     

Statistical method in quark combination model

We present a new method for solving the probability distribution for baryons,antibaryons,and mesons at the hadronization of the constituent quark and antiquark system.The hadronization is governed by the quark combination rule in the quark combination model developed by the Shandong Group.We employ the method of the generating function to derive the outcome of the quark combination rule,which is significantly simpler and easier to generalize than the original method.Furthermore,we use the formula of the quark combination rule and its generalization to study the property of the multiplicity distribution of net-protons.Taking a naive case of quark number fluctuations and correlations at hadronization,we calculate ratios of multiplicity cumulants of final-state net-protons and discuss the potential applicability of the quark combination model by studying hadronic multiplicity fluctuations and the underlying phase transition property in relativistic heavy-ion collisions.     

Search for heavy toplike quarks using lepton plus jets events in 1.96 TeV pp collisions

We present the results of a search for pair production of a new heavy toplike quark t' decaying to a W boson and another quark using the Collider Detector at Fermilab II detector in run II of the Tevatron pp collider. Using a data sample corresponding to 760 pb(-1) of integrated luminosity, we fit the observed spectrum of total transverse energy and reconstructed t' quark mass to a combination of standard model processes and t' pair production. We see no evidence for t't' production, and we infer a lower limit of 256 GeV/c(2) on the mass of the t' at 95% C.L. assuming standard strong couplings for the t'.     

Electromagnetic Coupling of Negative Parity Nucleon Resonances N(1535) Based on Nonrelativistic Constituent Quark Model

The electromagnetic transition between the nucleon and excited baryons has long been recognized as an important source of information for understanding strong interactions in the domain of quark confinement. We study the electromagnetic properties of the excitation of the negative parity the N~*(1535) resonances in the nonrelativistic constituent quark model at large momentum transfers and have performed a calculation the longitudinal and transverse helicity amplitudes. Since the helicity amplitudes depend strongly on the quark wave function in this paper, we consider the baryon as a simple, non-relativistically three-body quark model and also consider a hypercentral potential scheme for the internal baryon structure, which makes three-body forces among three quarks. Since the hyper central potential depends only on the hyper radius, therefore, the Cornell potential which is a combination of the Coulombic-like term plus a linear confining term is considered as the potential for interaction between quarks. In our work, in solving the Schrodinger equation with the Cornell potential, the Nikiforov–Uvarov method employed, and the analytic eigen-energies and eigen-functions obtained. By using the obtained eigen-functions, the transition amplitudes calculated. We show that our results in the range Q~2 2GeV~2 lead to an overall better agreement with the experimental data in comparison with the other three non-relativistic quark models.     

Constituent quarks in nuclear matter and the Nolen-Schiffer anomaly

We investigate the density dependence of the neutronproton mass difference using the Nambu and Jona-Las-inio model in combination with the Isgur-Karl constituent quark model. The decrease of the constituent quark masses with increasing density reduces then-p mass difference in the proper way to help resolving the Nolen-Schiffer anomaly. We point out however, that in the presence of vector interactions, this effect is less pronounced than previously suggested.     

Contribution of Quark Structure Term in Nucleon Electric and Magnetic Form Factors

The constituent quarks in the nucleon have always been considered as a point-like particle in the relativistic constituent quark model. However its calculation results of GnE agree poorly with the new experimental data. The electromagnetic structure of light front constituent quarks is considered in this paper. We find that the calculation results have good agreement with the new experimental data of GnE after considering the contribution of the quark structure term. This treatment seems to be able to improve the fit to experimental data of Gep/GMp, /Q2F2p/kpF1p,and Gen/GMn as well.     

Recent experimental data and the size of the quark in the constituent quark model

We use the constituent quark model (CQM) to describe CDF data on double parton cross section and HERA data on the ratio cross section of elastic and inelastic diffractive productions. Our estimate shows that the radius of the constituent quark turns out to be rather small, GeV^-2, in accordance with the assumption on which CQM is based. Received: 14 April 2002 / Published online: 9 August 2002     

Exotic Hadrons and Underlying Z2,3 Symmetries

The recent observation of higher quark combinations, tetraquarks and pentaquarks, is a strong indication of more exotic hadrons. Using Z₂ and Z₃ symmetries and standard model data, a general quark combination producing new hadronic states is proposed in terms of polygon geometries according to the Dynkin diagrams of  _n affine Lie algebras. It has been shown that Z_2,3 invariance is crucial in the determination of the mesonic or the baryonic nature of these states. The hexagonal geometry is considered in some details producing both mesonic and baryonic states. A general class of this family is also presented.     

Three-flavor quark mass dependence of baryon spectra in holographic QCD

We introduce the strange quark mass to the Sakai–Sugimoto model of holographic QCD. We compute mass shifts in the spectra of three-flavor baryons at the leading order in perturbation in quark masses. Comparison with experimental data shows an agreement only qualitatively.     

Weak form factors for semileptonic octet baryon decays in the chiral quark model

We study the weak vector and axial-vector form factors of first- and second-class currents for the semileptonic octet baryon decays in the spirit of the chiral quark model. Our results for the weak magnetism form factors are consistent with the conserved vector current (CVC) results. The induced pseudotensor form factors, which are highly model dependent, are small. The overall performance of the chiral quark model is quite good and in general agreement with existing experimental data. Received: 9 March 1998 / Published online: 12 August 1998     

Search for a heavy toplike quark in pp collisions at √s=1.96 TeV

We present the results of a search for pair production of a heavy toplike (t') quark decaying to Wq final states using data corresponding to an integrated luminosity of 5.6 fb(-1) collected by the CDF II detector in pp collisions at √s=1.96 TeV. We perform parallel searches for t'→Wb and t'→Wq (where q is a generic down-type quark) in events containing a lepton and four or more jets. By performing a fit to the two-dimensional distribution of total transverse energy versus reconstructed t' quark mass, we set upper limits on the t't' production cross section and exclude a standard model fourth-generation t' quark decaying to Wb (Wq) with mass below 358 (340) GeV/c(2) at 95% C.L.     

$ B \to D^{(*)}$ transitions in a quark model

We propose a constituent quark model to evaluate heavy decay constants and form factors relevant for semileptonic transitions. We show that the model reproduces the scaling laws dictated by the spin-flavor symmetry in the heavy quark limit and describes quite well the experimental data.Received: 29 December 2004, Published online: 21 February 2005     

Deconfinement Phase Transition Including Perturbative QCD Corrections in （Proto）neutron Star Matter

Deconlinement phase transition and neutrino trapping in （proto）neutron star matter are investigated in a chiral hadronic model （also referred to as the FST model） for the hadronic phase （HP） and in the color-flavor-locked （CFL） quark model for the deconlined quark phase. We include a perturbative QCD correction parameter αs in the CFL quark matter equation of states. It is shown that the CFL quark core with K^0 condensation forms in neutron star matter with the large value of αs. If the small value of αs is taken, hyperons suppress the CFL quark phase and the liP is dominant in the high-density region of （proto）neutron star matter. Neutrino trapping makes the fraction of the CFL quark matter decrease compared with those without neutrino trapping. Moreover, increasing the QCD correction parameter as or decreasing the bag constant B and the strange quark mass ms can make the fraction of the CFL quark matter increase, simultaneously, the fraction of neutrino in protoneutron star matter increases, too. The maximum masses and the corresponding radii of （proto）neutron stars are not sensitive to the QCD correction parameter αs.     

手征胶子修正夸克平均场模型

这项工作利用考虑π介子与胶子效应的夸克平均场模型研究原子核结构的基本性质。在夸克平均场中,核子由三个束缚在谐振子势场中的组分夸克构成。描述强相互作用的量子色动力学必须满足手征对称性,此外夸克之间也需要通过交换胶子相互作用。因此,在夸克平均场模型中,对利用夸克势获得的核子质量考虑π介子修正与胶子修正。通过少数稳定有限核的结合能与半径实验值确定模型中的未知参数,获得了一组夸克平均场相互作用参数,QMF-NK。利用该组参数计算40Ca和208Pb的电荷密度分布,发现与实验值符合很好。随后获得了与经验值一致的对称核物质的饱和性质。包含π介子修正和胶子修正的夸克平均场模型能够更好地描述有限核和核物质的性质。The basic properties of nuclear structure are studied within the quark mean field (QMF) model by taking the effects of pions and gluons into account. In QMF, the nucleon is made up of three constituent quarks confined by a harmonic oscillator potential. The quantum chromodynamics describing the strong interaction must satisfy the chiral symmetry and quarks interact with each other through exchange of gluons. Therefore pion correction and gluon correction are included in the nucleon mass obtained by using quark confinement potential in quark mean field model. We determine the unknown parameters in the model by fitting the experimental data of the binding energies and radii of several stable finite nuclei and obtain a set of parameters of quark mean field interaction, named QMF-NK. The charge density distributions of 40Ca and 208Pb are calculated, which are in good agreement with the experimental data. Later the saturation properties of symmetric nuclear matter which are consistent with the empirical data are obtained. With the pion and gluon corrections, the QMF model could treat finite nuclei and nuclear matter better.     

R_b and R_{\ell} in MSSM without R-parity

We examined and couplings in the minimal supersymmetric model with explicit trilinear R-parity violating interactions. We found that the top quark couplings and can give sizable contributions through top quark loops. When deriving the bounds from and data, we also take into account the loop contributions of R-parity conserving interactions. The bounds from are found to be stronger than those from and serve as the hitherto strongest bounds for some couplings. Received: 14 October 1999 / Revised version: 2 May 2001 / Published online: 8 June 2001     

Electromagnetic properties of relativistic quarks in confining potentials

We investigate electromagnetic properties of the quark core of nucleons in a model with massless quarks in confining potentials. We find quark core rms radii of 0.6 fm or smaller to be compatible with form factor data corrected for pion cloud effects. Relations between the magnetic form factor and the axial vector or pseudoscalar form factors will also be discussed.     

Covariant QCD modeling of light meson physics

We summarize recent progress in soft QCD modeling based on the set of Dyson-Schwinger equations truncated to ladder-rainbow level. This covariant approach to hadron physics accommodates quark confinement and implements the QCD one-loop renormalization group behavior. We compare the dressed quark propagator, pseudoscalar and vector meson masses as a function of quark mass, and the → ππ coupling to recent lattice-QCD data. The error in the Gell-Mann-Oakes-Renner relation with increasing quark mass is quantified by comparison to the exact pseudoscalar mass relation as evaluated within the ladder-rainbow Dyson-Schwinger model.