Distributions and correlations of constituent quarks in jets

In the frame of the quark recombination model, we study the momentum distributions and correlations of constituent quarks in jets by analyzing the final state hadrons generated by PYTHIA for the hard parton fragmentation processes in vacuum. Parameterizations for the distributions are tabulated.     

Distributions and correlations of constituent quarks in jets

In the frame of the quark recombination model, we study the momentum distributions and cor- relations of constituent quarks in jets by analyzing the final state hadrons generated by PYTHIA for the hard parton fragmentation processes in vacuum. Parameterizations for the distributions are tabulated.     

Hadron clusters with quark core and multiplicity distributions

Multiplicity distributions of ground state hadrons (pseudoscalar and vector meson nonet and baryon octet and decuplet) are investigated in a model of hadron clusters based of subsequent hadron emission by quarks. The effects of resonance decay for the observed (stable) hadron multiplicities are also considered. Average numbers of different hadrons are calculated as a function of the number of charged pions. The results are compared with available data and a good overall agreement is found.     

Color flows for the pro cess gg→ B c+ c+ $$\bar b$$

Contributions of various color flows to the cross section for the gluonic production of B_c mesons are calculated. This is essential for simulating events involving B_c mesons with the aid of the PYTHIA package because the method used in PYTHIA to perform the hadronization of final partons and hadron remnants depends on the type of color flow. A modified method of partition into color flows is proposed.     

Production and hadronization of heavy quarks

Heavy long-lived quarks, i.e. charm and bottom, are frequently studied both as tests of QCD and as probes for other physics aspects within and beyond the standard model. The long lifetime implies that charm and bottom hadrons are formed and observed. This hadronization process cannot be studied in isolation, but depends on the production environment. Within the framework of the string model, a major effect is the drag from the other end of the string that the c/b quark belongs to. In extreme cases, a small-mass string can collapse to a single hadron, thereby giving a non-universal flavor composition to the produced hadrons. We here develop and present a detailed model for the charm/bottom hadronization process, involving the various aspects of string fragmentation and collapse, and put it in the context of several heavy-flavor production sources. Applications are presented from fixed-target to LHC energies. Received: 15 May 2000 / Published online: 9 August 2000     

The potential model of colored quarks: Success for single-hadron states, failure for hadron-hadron interactions

The success of the additive potential model of colored quarks for the masses, decay rates, and other properties of single mesons and baryons does not imply that this model can yield the observed meson-nucleon and nucleon-nucleon interactions. We give a comprehensive discussion of this issue. In agreement with previous authors, we conclude that, on the contrary, this model predicts inverse-power color-analog van der Waals potentials between separated hadrons which are in substantial contradiction with experimental data. We also discuss pathologies of non-abelian confining potentials, and show that the hamiltonian is unbounded below for an arbitrary number of quarks and antiquarks in a definite color state for all color states, except the singlet, triplet, and antitriplet.     

2004年诺贝尔物理奖介绍:渐近自由

描述粒子相互作用基本理论是标准模型，按照标准模型，强子是由夸克和反夸克通过色相互作用组成，色相互作用有一种特殊的性质：渐近自由，格罗斯、波利策和维尔切克由于确定地发现色相互作用的渐近自由性质获2004年诺贝尔物理奖。     

Study on‘soft＇ and ‘hard＇ interactions in ^-pp （pp） collisions using HIJING and PYTHIA

This paper presents a study on ＇hard＇ and ＇soft＇ interactions in ^-pp （pp） collisions using a phenomenological model of HIJING, the jet-cone reconstruction method is employed to select the ＇hard＇ and ＇soft＇ event sub-samples from minimum bias events. It is found that the HIJING model can reproduce the energy scaling behaviour of mean transverse momentum （〈PT〉） distributions of charged hadrons versus multiplicity （Nch） in ＇soft＇ events. From the PYTHIA simulation comparing with the HIJING model, the enhancement of the kaon and proton yields from ＇hard＇ interactions comparing with ＇soft＇ interactions is observed to be due to the mini-jets effect. These mechanisms responsible for the increase of charged hadron＇s （PT） are different in ＇soft＇ and ＇hard＇ interactions.     

Asymmetry in charmed-particle production in a Σ− beam

We present a calculation of the inclusive x _F distributions of charmed hadrons produced in a high-energy Σ^? beam. The calculation is based on the modified mechanism of charmed-quark fragmentation, as well as on the mechanism of c-quark recombination with the valence quarks from initial hadrons. We predict additional asymmetry in the production of charmed hadrons due to different distributions of the valence s and d quarks in a Σ^? beam.     

相对论重离子碰撞中强子气体膨胀过程的蒙特卡罗研究

利用AMPT蒙特卡罗产生器中的强子化程序模块ART1.0, 得到了强子化过程的演化图形, 并基于强子在不同时刻的空间分布图, 估算出了不同时刻的反应区域半径. 将所得结果与根据HBT关联得到的结果相比较, 定出了冻结为强子气体的时刻, 得到了合理的结果.     

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     

Inclusive production of charged hadrons and {\rm K}^0_{\rm S} mesons in photon–photon collisions

The production of charged hadrons and mesons in the collisions of quasi-real photons has been measured using the OPAL detector at LEP. The data were taken at centre-of-mass energies of 161 and 172 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the charged hadrons and mesons have been compared to the leading order Monte Carlo simulations of PHOJET and PYTHIA and to perturbative next-to-leading order (NLO) QCD calculations. The distributions have been measured in the range GeV of the hadronic invariant mass W. By comparing the transverse momentum distribution of charged hadrons measured in interactions with -proton and meson-proton data we find evidence for hard photon interactions in addition to the purely hadronic photon interactions. Received: 4 June 1998 / Published online: 6 November 1998     

Advantages of the color octet gluon picture

It is pointed out that there are several advantages in abstracting properties of hadrons and their currents from a Yang-Mills gauge model based on colored quarks and color octet gluons.     

Clocking hadronization in relativistic heavy-Ion collisions with balance functions

A novel state of matter has been hypothesized to exist during the early stage of relativistic heavy-ion collisions, with normal hadrons not appearing until several fm/c after the start of the reaction. To test this hypothesis, correlations between charges and their associated anticharges are evaluated with the use of balance functions. It is shown that late-stage hadronization is characterized by tightly correlated charge-anticharge pairs when measured as a function of relative rapidity.     

The HFT,a Heavy Flavor Tracker for STAR

Determining the degree of termalisation of the medium created in heavy ion collisions at RHIC remains highly debated. Elliptic flow (v₂) measurements at RHIC have already suggested the development of collectivity among partons before hadronization. If heavy flavor hadrons flow with the light flavor hadrons, this indicates frequent interactions between the light (u, d ,s) and heavy (c, b) quarks. Thus, thermalization of light quarks is likely to have been reached through partonic re-scattering. Experimentally this can be probed by making a direct measurement of D-mesons v₂ with sufficient precision at low transverse momentum. Using the Heavy Flavor Tracker (HFT) detector, the STAR experiment at RHIC is proposing to both study this process and also to directly reconstruct charmed hadrons (D⁰, D⁺, D_s, Λ_C, ...), using the displaced vertices of their decay products. The HFT is the first vertex detector to use a new and promising CMOS active pixel sensor technology. It will allow to build a relatively fast, accurate and radiation tolerant detector, while keeping the material budget low (∼0.3%X₀ per layer). Detector design and physics performance simulations are presented.     

Nonequilibrium parton dynamics in the strongly interacting QGP

The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for partons (DQPM) matched to reproduce recent lattice-QCD results—including the partonic equation of state—in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark-antiquark pairs or three quarks (antiquarks), respectively, obeying flavor current-conservation, color neutrality as well as energymomentum conservation. Since the dynamical quarks and antiquarks become very massive close to the phase transition, the formed resonant ‘pre-hadronic’ color-dipole states (q [`(q)]\bar q or qqq) are of high invariant mass, too, and sequentially decay to the groundstate meson and baryon octets increasing the total entropy. When applying the PHSD approach to Pb + Pb colllisions at 158 A GeV we find a significant effect of the partonic phase on the production of multi-strange antibaryons due to a slightly enhanced s [`(q)]\bar q pair production from massive time-like gluon decay and a larger formation of antibaryons in the hadronization process.     

Phenomenology of single-spin effects in hadron production at high energies

Within a phenomenological model, experimental data on the transverse single-spin asymmetry (A _N ) and polarization (P _N ) of hadrons are analyzed for 68 different inclusive reactions in hadron-hadron, hadron-nucleus, nucleus-nucleus, and lepton-nucleon interactions. A mechanism that is based on the interaction of the chromomagnetic moment of massive constituent quarks with the effective nonuniform chromomagnetic field of QCD strings formed after the initial color exchange is considered as the origin of single-spin effects. Quark-spin precession in the chromomagnetic field is taken into account. Dynamical masses and anomalous chromomagnetic moments are estimated for constituent u, d, s, c, and b quarks.