Investigation of charged-hadron production in proton–nucleus interactions at the energy of 50 GeV

Cross sections for the production of high-transverse-momentum charged hadrons in proton–nucleus interactions at the incident-proton energy of 50 GeV were measured with the aid of the FODS double-arm spectrometer. Single hadrons (charged pions and protons) emitted at a c.m. angle of about 90° and high-effective-mass pairs of hadrons flying apart at a c.m. angle of 180° were detected simultaneously. Results on the production of single hadrons are presented.     

Formation time of hadrons and density of matter produced in relativistic heavy-ion collisions

Density of matter produced in relativistic heavy-ion collisions depends substantially on the spacetime evolution of the collision and on the formation time of hadrons produced. Interactions of hadrons younger than their formation time are attenuated with respect to their normal values (transparency of hadronic matter for newly formed hadrons). The system of secondary hadrons produced in a heavy-ion collision thus expands as a gas of almost non interacting particles before hadrons reach their formation time. Densities of interacting hadronic matter produced in oxygen-lead and sulphur-lead collisions at 200 GeV/nucleon are estimated as a function of the formation time of hadrons. Uncertainties in our knowledge of the critical temepratureT _c and of the formation time of hadrons τ₀ permit at present three scenarios: an optimistic one (QGP has already been produced in collisions of oxygen and sulphur with heavy ions and will be copiously produced in Lead collisions), a pessimistic one (QGP cannot be produced at 200 GeV/nucleon) and an intermediate one (QGP has not been produced in oxygen and sulphur interactions with heavy ions and will be at best produced only marginally in Pb-collisions). We find the last opinion as most probable.     

Heavy quark systems and hadron mass spectra

The influence of chromomagnetic hyperfine interaction onB andT hadrons is studied. The colour magnetic moments are related to the hyperfine splittings of hadrons.     

STATIC PHYSICAL PROPORTIES OF HADRONS CALCULATED IN THE SOLITON BAG MODEL

In this paper,the Mean-Field Approximation is applied to the soliton bag model to calculate static physical proporties of hadrons of hadrons numerically.After taking account of the quark masses and the corrections of the center of mass the g_A/g_V value is improved evidently and the hadron mass spectrum,the r.m.s charge radius and the magnetic moments of the hadrons are basically in agreement with their experimental values.A preliminary derivation of the mass differencs between the d and u guarks is presented.     

Spin physics in the high energy hadron productions. A systematic study of the spin asymmetries induced by <Emphasis Type="Italic">pp, γp,ep</Emphasis> and λ<Emphasis Type="Italic">p</Emphasis> collisions

The spin polarizations of hadrons inclusively produced by pp, γp and λp collisions are studied by the quark rearrangement model. The present model is a phenomenological one based on the relativistic spin equations of motion and using the quark distribution functions in hadrons and photon. A general success of the model is demonstrated. We find usefulness of the present formulation for studying the dynamics producing spin asymmetry distributions and the statics determining signs and magnitudes of the spin polarization by reflecting the characteristic quark structure in hadrons.     

Hydrodynamical model of electron-positron annihilation into hadrons

Landau's hydrodynamical model of multiparticle production is formulated for e⁺e^? → hadrons at center-of-momentum energies 10 GeV and higher. An analytical solution to the problem of spherical expansion of a relativistic fluid is presented. When hadrons condense out at the last stage of expansion, fluid thermal motion is taken into account. We derive predictions for multiplicities, average secondary energies and inclusive single particle distributions for various secondary hadrons; these results are then compared to other models. Finally, we investigate the internal consistency of the model.     

Exotic hadron bound state production at hadron colliders

The non-relativistic wave function framework is applied to study the production and decay of exotic hadrons, which can be effectively described as bound states of other hadrons. Employing the factorized formulation,with the help of event generators, we investigate the production of exotic hadrons in multiproduction processes at high energy hadron colliders. This study provides crucial information for the measurements of the relevant exotic hadrons.     

Electron-positron annihilation into hadrons at high energies

In the limit of extremely high energies with the transverse momentum of each hadron fixed, the reaction e⁺ + e⁻ → hadrons proceeds by the annihilation of this pair into two virtual photons which turn into two fireballs of hadrons with negligible final-state interaction.     

袋模型进展

本文回顾了强子结构袋模型几年来所取得进展,着重介绍近两年来的进展。总结是沿以下三个方面进行的,(一)理论描述的进一步完善,包括半定量地介绍了R.L.Jaffe等人最近提出的,考虑到手征对称的混合袋模型。(二)袋模型对强子静态性质的应用,包括轻夸克强子和重夸克强子的质量谱,以及对π介子质量的重新考虑。(三)多夸克强子,分析了它们分类情况,并估计了它们的质量。袋模型对于强子衰变,强子碰撞等动态过程,以及对原子核的应用成就不多,进展不大,而且篇幅有限,未作定量介绍。     

Production of two largeP T hadrons from hadronic collisions

We study the production of two largeP _T hadrons from hadronic collisions at next to leading order. The formalism developed allows to consider either the inclusive case or the isolated one, where the transverse hadronic energy within a cone around the produced hadrons is restricted.     

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.     

Flow measurements via two-particle azimuthal correlations in Au + Au collisions at sqrt [s(NN)]=130 GeV

Two-particle azimuthal correlation functions are presented for charged hadrons produced in Au+Au collisions at the Relativistic Heavy Ion Collider (sqrt [s(NN)]=130 GeV). The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values (v2) show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone epsilon, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low p(T). A breakdown of this epsilon scaling is observed for charged hadrons with pT >1.0 GeV/c.     

Multiplicity distributions in a thermodynamical model of hadron production ine + e − collisions

Predictions of a thermodynamical model of hadron production for multiplicity distribution ine ⁺ e ^? annihilations at LEP and PEP-PETRA centre of mass energies are shown. The production process is described as a two-step process in which primary hadrons emitted from the thermal source decay into final observable particles. The final charged tracks multiplicity distributions turn out to be of Negative Binomial type and are in quite good agreement with experimental observations. The average number of clans calculated from fitted Negative Binomial coincides with the average number of primary hadrons predicted by the thermodynamical model, suggesting that clans should be identified with primary hadrons.     

Annihilation of e+−e− into hadrons in a hydrodynamic model

A hydrodynamic model with modified boundary conditions is proposed for the two-jet component of e⁺?e^? annihilation into hadrons. Satisfactory agreement with data for charged multiplicity and inclusive distributions of hadrons is obtained with three energy-independent parameters.     

Colour intransparency and the cross sections for colour-singlet and colour-octet hadrons in the Low-Nussinov model

The dependence of cross sections on the colour state of the colliding hadrons is investigated within the Low-Nussinov model of two-gluon exchange. The total cross sections for colour-octet hadrons are practically constant as functions of the hadronic radii, while they tend to zero when the radii of the colour-singlet hadrons approach zero. The slope parameter of the differential clastic cross sections for small momentum transfers is rather insensitive to the colour structure of the colliding hadrons. The integrated colour exchange cross section is calculated.     

Collective Perspective on Advances in Dyson-Schwinger Equation QCD

We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small- to large-Q²; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.     

Strong decays of newly observed heavy flavor hadrons

In this talk, we briefly review the experimental status of newly observed charmed hadrons during the past years. Then we introduce the theoretical progresses on these charmed hadrons, especially our studies on the strong decays of new charmed hadrons during the past one year.     

Collective Perspective on Advances in Dyson–Schwinger Equation QCD

We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small-to large-Q2; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.     

Hadron production by ep collisions at HERA

TheP distribution of hadrons from deep-inelastic ep collisions of the H1 experiment determines for the hadrons in the final state, a temperature 277±14 MeV220 MeV of the critical temperature predicted by QCD, suggesting the formation of quark-gluon plasma (QGP). From their forward to backward ratio, it is found an excess of hadrons arising from the deconfinement of quarks inside the proton.