Quark Structure Of Hadrons Research Articles

Baryon chiral perturbation theory extended beyond the low-energy region.

We consider an extension of the one-nucleon sector of baryon chiral perturbation theory beyond the low-energy region. The applicability of this approach for higher energies is restricted to small scattering angles, i.e. the kinematical region, where the quark structure of hadrons cannot be resolved. The main idea is to re-arrange the low-energy effective Lagrangian according to a new power counting and to exploit the freedom of the choice of the renormalization condition for loop diagrams. We generalize the extended on-mass-shell scheme for the one-nucleon sector of baryon chiral perturbation theory by choosing a sliding scale, that is, we expand the physical amplitudes around kinematical points beyond the threshold. This requires the introduction of complex-valued renormalized coupling constants, which can be either extracted from experimental data, or calculated using the renormalization group evolution of coupling constants fixed in threshold region.

Exclusive processes and the fundamental structure of hadrons

I review the historical development of QCD predictions for exclusive hadronic processes, beginning with constituent counting rules and the quark interchange mechanism, phenomena which gave early validation for the quark structure of hadrons. The subsequent development of pQCD factorization theorems for hard exclusive amplitudes and the development of evolution equations for the hadron distribution amplitudes provided a rigorous framework for calculating hadronic form factors and hard scattering exclusive scattering processes at high momentum transfer. I also give a brief introduction to the field of "light-front holography" and the insights it brings to quark confinement, the behavior of the QCD coupling in the nonperturbative domain, as well as hadron spectroscopy and the dynamics of exclusive processes.

Single-spin physics: experimental trends and their origin

The review of experimental trends in the physics of single-spin processes and their origin in the framework of an effective color field model is presented. A global analysis of polarization data for a large set of different reactions in h-h, h-A, A-A and lepton-A collisions is performed. In particular, the single-spin asymmetry, the polarization of hyperons and antihyperons are analyzed. The analysis revealed many common trends in the behavior of the experimental data, depending on the kinematic variables, the quark structure of hadrons and the mass of the colliding ions. The origin of large single-spin effects can be attributed to the influence of force such as the Stern-Gerlach-like one in a chromomagnetic field and to the Thomas precession in chromoelectric component of the Effective Color Field (ECF). Precession of the spin of the quarks in a chromomagnetic field is a major cause of the oscillation of the polarization as a function of kinematic variables. Focusing of quarks in the ECF leads to the resonant energy dependence of the single-spin observables. The predictions of large single-spin effects for the different reactions are presented, in particular, the expected oscillations of SSA and polarization, as well as change their sign at RHIC energies due to the growth of ECF with increasing reaction energy or the atomic weight of the ions. The Quark Counting Rules determine the sign and magnitude of the ECF.

Polarization effects in Drell-Yan processes

Effects of polarization of hadrons and constituent quarks in Drell-Yan processes are considered; they are one of the most efficient tools for investigation of the quark structure of hadrons. Special attention is paid to such important parton distribution functions as the transversity and T-odd Sivers and Boer—Mulders functions whose study is necessary for understanding the effects connected with the nonzero transverse component of the quark momentum. An original method for direct extraction of transversity and Boer—Mulders function in the proton from the data on Drell—Yan processes, in which a maximum of one hadron in the initial state is transversely polarized, is presented. This method possesses a number of important advantages. The method is applied both to Drell—Yan processes with a valence antiquark (antiproton-proton and pion-proton collisions) and with a sea antiquark (proton-proton, proton-deuteron, and deuteron-deuteron collisions). Theoretical estimates of asymmetries and cross sections for setups at RHIC (BNL, US), NICA (JINR, Russia), COMPASS (CERN, Switzerland), PAX (GSI, Germany), and J-PARC (Japan) are presented for evaluation of the measurability of transversity and T-odd distributions. These theoretical estimates are accompanied by calculations of statistical uncertainties for measured asymmetries using the new Monte Carlo generator of Drell—Yan events. The duality of Drell—Yan processes and those of production of J/Φ resonance is studied, and it may allow one to considerably reduce statistical uncertainties of parton distributions. Kinematical conditions, for which this duality can be observed, are evaluated.

Hadron diffractive processes: the structure of soft pomeron and colour screening

On the basis of the experimental data on diffractive processes in πp, pp and p¯p collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality of cross sections such as σtot πp/σtot pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion and proton (antiproton) in the impact parameter space of quarks, σπ(r 1⊥, r 2⊥; s) and σp(r 1⊥, r 2⊥, r 3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r i⊥−r k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented.

THE OZI RULE AND NUCLEONS

The title of this lecture series raises two questions: (1) what is the OZI rule? (2) what is a nucleon. In the lectures both questions were addressed in parallel and the material moved back and forth between them. In a written version it seems more appropriate to treat the two questions separately, beginning with trying to understand the structure of the nucleon. Experimental evidence for the symmetry and quark structure of hadrons is reviewed with a historical introduction and updated by presenting constituent quark model relations for hadron masses and magnetic moments. Three definitions of the OZI rule are presented, all of which forbid decays like ϕ → ρπ but making different selection rules for more complicated reactions. All suffer from the higher order paradox that a forbidden process can take place via a two-step transition in which each step is allowed; e.g. [Formula: see text]. No prescription is given for estimating the strength of forbidden processes. The role of cancellations between different higher order diagrams is discussed.

Possible mass-spin relation for the hadron resonances as an extended object

The results on mass-spin relation are presented, based on the assumption that hadron resonances construct a (2+1) 3-dimensional world with constant curvature in (3+1) flat Minkowski space. It is shown that the qualitative features of hadron mass spectrum are obtained from the mass eigenvalue equation under a suitable boundary condition related to the extensions of the excited states of hadrons in Minkowski space-time. If the fundamental physical constant of strong interactionl is quantized (ls1,ls2, …), ordinary hadron resonances consisting of u, d, s quarks are explained byls1, …,ls8 and the critical valuesls1,ls3,ls9 correspond to the masses of t, b, c quarks, respectively. Motivated by these results, we are able to have the idea that the quark structure of hadrons can be reduced to the properties of internal space-time itself.

Secondary particle spectra in hadron-hadron and hadron-nucleus collisions in the framework of the additive quark model and quark statistics

Secondary meson and baryon inclusive spectra in high-energy hadron-nucleon and hadron-nucleus collisions are calculated. We suggest that the fragmentation hadrons are produced as a result of the spectator mechanism and that their distributions imitate those of the quark-spectator. Sea hadron distributions are supposed to be similar to that of the hadron ones ine+e− annihilation. Particle production ratios are borrowed from statistic rules. Comparison with the experiment manifests the success of the quasinuclear quark structure of hadrons.

Hadronic poles andΩ−nonleptonic decays

Separable contributions to the ${\ensuremath{\Omega}}^{\ensuremath{-}}$ nonleptonic decays are replaced by $K$-meson poles. This leads to a theoretical description which shows that the experimental results support general theoretical ideas such as the Weinberg-Salam electroweak theory, QCD, and SU(6) quark structure of hadrons.

Fermions in scalar and vector potentials

This paper investigates the basic physical properties of spin-1/2 bound states, using numerical solutions of the Dirac equation to illustrate the distinctive differences between scalar and vector binding. The results are discussed in relation both to the quark structure of hadrons and to the further possibility that quarks and leptons might themselves be composite. The effect of scalar and vector potential strengths, separately and in combination, on energy levels and magnetic moments is discussed, together with the energy and potential dependence of the wave function parameters 〈1/r〉, 〈p2〉1/2 and ψ2(0), which provide the coefficients in perturbative mass formulae based on the Fermi-Breit Hamiltonian. The results are used to reassess a number of topics, including the ground-state meson and baryon mass spectrum, vector-meson leptonic-decay widths, effective quark mass and the shape of the confining potential.

Yields of projectile fragments in hadron-nucleus interactions and the quark structure of hadrons

Multiplicities of secondary hadrons in the fragmentation region of a projectile are computed as a function of the atomic number of the target, A. The calculation is based on the notion of a nucleon (meson) composed of three (two) spatially discrete constituent quarks. For an incident proton, yields of secondary nucleons near x = 2 3 (as well as π − or K + mesons near x = 1 3 ) are determined solely by the magnitude of the quark-nucleon cross section, assumed to be ∼ 1 3 of the inelastic proton-proton cross section, and the distribution of nuclear matter. Our results agree well with the data on A dependence of the p, π − and K + yields in proton-nucleus collisions. Predictions are given for the A dependence of the projectile fragment yields in the cases of π, K and hyperon beams.

Quark model for multiparticle and inclusive reactions

The relative multiplicity of different hadrons produced in high-energy collisions is found in the framework of the quark model. Appart from the usual hypothesis about the quark structure of hadrons, two extra assumptions are made. Firstly, produced particles are supposed to be mainly the members of the meson 36-plet and baryon (antibaryon) 56-plet. Secondly, production of strange quarks is assumed to be suppressed relative to non-strange quarks roughly by a factor of three, as taken from experiment. In the small- x region the agreement with experimental data is satisfactory. In the fragmentation region it is necessary to take into account the kinematics of the resonant state's decay. The influence of such decay on the x and p T 2 distributions of hadrons is discussed.