Hadron Physics 2000

The following sections are included:

• Foreword

• CONTENTS

A fundamental question in QCD is the non-perturbative structure of hadrons at the amplitude level—not just the single-particle flavor, momentum, and helicity distributions of the quark constituents, but also the multi-quark, gluonic, and hidden-color correlations intrinsic to hadronic and nuclear wavefunctions. The light-cone Fock-state representation of QCD encodes the properties of a hadrons in terms of frame-independent wavefunctions. A number of applications are discussed, including semileptonic B decays, deeply virtual Compton scattering, and dynamical higher twist effects in inclusive reactions. A new type of jet production reaction, "self-resolving diffractive interactions" can provide direct information on the light-cone wavefunctions of hadrons in terms of their quark and gluon degrees of freedom as well as the composition of nuclei in terms of their nucleon and mesonic degrees of freedom. The relation of the intrinsic sea to the light-cone wavefunctions is discussed. The physics of light-cone wavefunctions is illustrated for the quantum fluctuations of an electron.

The subject of effective interactions is introduced and applications in both quantum mechanics and quantum field theory are presented. In particular the use of chiral perturbation theory as an effective low energy description of QCD is developed and it is argued that such methods really are effective in both the meson and baryonic sectors.

Relativistic Heavy Ion Collider at BNL has just begun its operation, colliding the nuclei of Gold at unprecedented energies. RHIC is a dedicated QCD machine, and in these lectures I discuss some topics in the physics of hot and dense QCD matter that can be addressed there. The following subjects are considered in the present three lectures: 1. Introduction to the physics of RHIC. 2. Heavy quarkonium as a probe of QCD dynamics. 3. Topological fluctuations near the deconfinement phase transition and the possibility of P and CP violation in hot QCD.

We discuss various ideas on the nonperturbative vacuum structure in QCD. The stochastic vacuum model of Dosch and Simonov is presented in some detail. We show how this model produces confinement. The model incorporates the idea of the QCD vacuum acting like a dual superconductor due to an effective chromomagnetic monopole condensate. We turn then to high energy, small momentum transfer hadron-hadron scattering. A field-theoretic formalism to treat these reactions is developed, where the basic quantities governing the scattering amplitudes are correlation functions of light-like Wegner-Wilson lines and loops. The evaluation of these correlation functions with the help of the Minkowskian version of the stochastic vacuum model is discussed. The comparison with experiment gives satisfactory results and allows for instance a determination of the string tension from high energy proton-proton elastic scattering.

We review the 25 year old history of activities of Brazilian physicists in areas related to hadronic physics.

We construct improved QCD sum rules for the nucleon magnetic moments by implementing direct-instanton contributions to the operator product expansion of the nucleon correlator in a magnetic background field. The instanton contributions are found to affect only those sum rules which had previously been considered unstable. The new sum rules show a high degree of stability and reproduce the experimental values of the nucleon magnetic moments for values of the magnetic quark condensate susceptibility which are consistent with other estimates. (Invited talk given at "Hadron Physics 2000", Caraguatatuba, São Paulo, Brazil (April 10-15, 2000).

A variational principle for out of equilibrium systems is used to derive the equations of motion for the quantum fluctuations of the λɸ⁴ model in the presence of condensates, i.e., in the asymmetric phase of the potential. For the system in thermal equilibrium a generalized linear response calculation is developed. It yields generalized time-dependent correlation functions. In the limit corresponding to the gaussian approximation the numerical temporal evolution of the equations is performed in a lattice of 1+1 dimensions given non-homogeneous initial configurations for the classical field as well as for the fluctuations. These initial conditions correspond to high energy density localized regions which expands.

We discuss, in the framework of the bound state approach to SU(3) Skyrme model, the baryonic number–two strange sector. We study situations where the baryons involved are bound to form dibaryons and where free baryons are simply scattered. In the first case, the dibaryon spectrum is calculated with a generalized axially symmetric ansatz. A prediction about the existence of the H–particle is also made. In the second case we use the product ansatz to develop a formalism to study the general baryon–baryon interaction potential. Results are presented for the ΛN interaction.

High temperature symmetry nonrestoration may have very important consequences in cosmology. Usually this phenomenon shows up in multi-field theories such as the O(N₁) × O(N₂) scalar model studied in this work. Here we use the δ expansion and the imaginary time formalism to evaluate thermal masses up to two-loop in a perturbative way. Apart from strongly supporting symmetry nonrestoration, our results reveal the possibility of other high temperature symmetry breaking patterns for which the last term in the breaking sequence is O(N₁ - 1) × O(N₂ - 1).

We study color superconductivity in external magnetic field. We discuss the reason why the mixing angles in color-flavor locked (CFL) and two-flavor superconductivity (2SC) phases are different despite the fact that the CFL gap goes to the 2SC gap for m_s → ∞. Although flavor symmetry is explicitly broken in external magnetic field, we show that all values of gaps in their coset spaces of possible solutions in the CFL phase are equivalent in external magnetic field.

The following sections are included:

• Central Potential

• Kernel

• Application

• Conclusions

• References

Compton scattering on the deuteron is studied in the framework of baryon chiral perturbation theory to third order in small momenta, for photon energies of order the pion mass. The scattering amplitude is a sum of one- and two-nucleon mechanisms with no undetermined parameters. Our results are in good agreement with the intermediate energy experimental data, and a comparison is made with the recent higher-energy data obtained at SAL.

As is well known, the exchange of a single pion does not contribute to scattering of nucleons by isoscalar targets, since the pion is an isovector. This simple idea were employed in a recent work in order to probe the next layer of NN interaction and we showed that a clear dependence of phase shifts on the NN potential is obtained. As Nα scattering data is still not free of ambiguity, few conclusions can be extracted.

Motivated by more precise Nd scattering data recently available, we began a new study of Nd system. This may give us more information about the intermediate region of NN potential, but first we need to study the techniques involved in extracting phase shifts and mixing parameters.

We compare pion-nucleon amplitude calculated from chiral perturbation theory up to with the leading contribution, for pion laboratory momenta up to 200 MeV. We also compare the low energy current algebra pion-nucleon amplitude with its unitarity corrections recently obtained. From these comparisons, we conclude that, even close to threshold, both methods lead to important corrections to the amplitudes, mainly for P-waves.

In order to obtain a good fit to we propose an effective potential model which the up and down quarks are confined with different strengths. We choose the harmonic oscillator, with equal components S+V because of analitical results in the Dirac equation we can obtain. The total momentum results very close to 1.

The aim of this work is to calculate the complete order 1/N_c corrections to the baryon masses in the bound state approach to the three flavor Skyrme model. We consider the strange-strange interactions which take the form of a meson-meson interaction in the expansion of the chiral Lagrangian to quartic order in the kaon fields. This type of interaction has been neglected in previous treatments. We perform the complete calculation for the quadratic Lagrangian in derivatives.

In a previous work we discussed the construction of an ansatz to derive the NN interaction in the sudden approximation in the Skyrme model. We discuss the quantization problem and show the corresponding results for the potential. Comparisons of the results with other existent potentials show that the present proposal constitutes a plausible solution to the problem.

Non-leptonic hyperon weak decays are investigated in the SU(3) Skyrme model. We follow a collective coordinate scheme in which the symmetry breaking terms in the strong effective action are diagonalized exactly. To describe the weak interactions we use an octet dominated weak effective lagrangian that leads to a good description of the known 2π and 3π kaon decays. We show that the observed S-wave decays are reasonably well reproduced in the model. On the other hand, our calculated P-wave amplitudes do not agree with the empirical ones even though both pole and contact contributions to these amplitudes are properly taken into account.

In this work we study a new version of the fuzzy bag model (FBM). The main point of this work is the inclusion of energy-momentum conservation in the model. This feature is lacking in the original formulation¹, but it is of paramout importance to turn the model into a real bag model. In our version of the FBM, the size of the bag will be determined by the equilibrium of the outward pressure of the quarks with the inward pressure of the vacuum, just like in the MIT bag model. As a side remark, we note that a first consequence of our model is that the bag "constant" B will not be a constant even for the ground state — it will be a function of the radial variable r.

Exact analytic solutions are found to the Dirac equation for a combination of Lorentz scalar and vector Coulombic potentials with additional non-Coulombic parts. An appropriate linear combination of Lorentz scalar and vector non-Coulombic potentials, with the scalar part dominating, can be chosen to give exact analytic Dirac wave functions.

We investigate the soft (nonperturbative) and hard (perturbative) contributions in the processes of ɸ and ψ photoproduction, studying the energy dependence of the integrated elastic cross sections and the t dependence of the differential cross sections. We show that a coherent sum of the pQCD and conventional soft Pomeron contributions provides good reproduction of the experimental data. The hard contribution is based on a pQCD calculation with screening corrections (SC). The soft part is assumed to have the energy dependence and the shrinking forward peak characteristic of the hadronic interactions at high energies.

We study the production and signatures of heavy exotic quarks pairs at LHC in the framework of the vector singlet model (VSM), vector doublet model (VDM) and fermion-mirror-fermion (FMF) model. The pair production cross sections for the electroweak and strong sector are computed.

In this paper we study the possibilities of the production and decay of one of the 3-3-1 exotic quarks at CERN LEPII-LHC collider. For typical vector bilepton, exotic quark masses and mixing angles we obtained between 20 and 750 events per year.

The following sections are included:

• Introduction

• The Firetube Model for Hadron-Nucleus Collisions

• Charm Production

• References

The following sections are included:

• Introduction

• The Forward Proton Detector

• Diffractive Physics and the FPD

• Acknowledgments

• References

In this contribution different approaches to generate a gluon mass are discussed. More specifically a recent result for the gluon propagator with a dynamical mass, proposed by Gorbar and Natale, is used in connection with the Landshoff-Nachtmann model for the Pomeron to describe the elastic differential cross section for pp scattering, with good agreement.

Back-to-back correlations of asymptotic fermion–anti-fermion pairs appear if in-medium interactions lead to mass modifications of fermion states in a thermalized medium. The back-to-back correlations of protons and anti-protons will be experimentally observable in ultrarelativistic heavy ion collisions. The strength of back-to-back correlations of fermions can be unlimitedly large, diverging as the momentum of the pair increases and the net baryon density decreases.

The effect of continuous emission hypothesis on the two-pion Bose-Einstein correlation is discussed and compared with the corresponding results based on the usual freeze-out ansatz. Sizable differences in the correlation function are observed when comparing these two scenarios of the decoupling process. They could lead to entirely different interpretation of properties of the hot matter formed in high-energy heavy-ion collisions.

We present a preliminary study of asymmetries in the production of in 500 GeVc π^- - nucleon interactions. These processes occur at low and not very high energy , then we can use the Dual Parton Model. In the frame of this model we use the graphs of interchange of pomerons to calculate the cross section production of Λ⁰ and as funtion of Feynman-x x_F.

Photonuclear reactions provide an efficient mechanism of pion, kaons and hyperon production in the intermediate energy range. We present here a discussion on the effect of binding energy on particle production mechanism, by mean of the change in the barionic effective mass. The residual-nuclei characteristic calculated by the multicollisional intranuclear cascade model and the emission of hadrons during the rapid phase of the photonuclear is also discussed.

In the hadron-exchange model of annihilation into two pions, Δ exchange is known to make a significant contribution. A preliminary investigation of annihilation into three pions suggested that Δ-exchange effects are much smaller for this process. However, complete consistency between the treatments of the two- and three-pion channels was not achieved in previous work. In the present contribution, we perform a comparison of Δ exchange effects in the two- and three-pion channels, treating both channels consistently within the same model.

We investigate the possibility that four-fermion contact interactions give rise to the observed deviation from the Standard Model prediction for the weak charge of cesium, through one-loop contributions. We show that the presence of loops involving the third generation quarks can explain such deviation.

We use the QCD Sum Rule approach to evaluate the form factors and decay rates of decay. This decay is represented by a three point function of the weak transition current and the interpolating fields of Λ_b and Λ_c. We calculate the theoretical part by performing the Operator Product Expantion of this three point function. In the phenomenological side, we use the experimental information of the decay amplitude. As usual we perform a Borel transform in these two sides in order to obtain the form factors. With this information we can obtain the decay rates. After the calculation of these quantities we compare our results with the experimental ones.

We report a theoretical study on electron scattering by CS₂ molecules in the low and intermediate energy range. More specifically, the calculated elastic differencial, integral, and grand total cross sections are determined for electron impact energies up to 100 eV. A complex optical interaction potential, derived from a Hartree-Fock self consistent field (SCF), is applied to describe the electron-molecule interaction. The Lippmann-Schwinger scattering equations are solved using the Schwinger variational iterative method combined with the distorted-wave approximation. The comparison between the calculated cross sections and the available experimental data in this energy range shows the importance of polarization and absorption effects in these collision processes.

Using recent experimental evidence from E791 on the sigma meson in D → 3π decays, we study the relevant couplings in D → σπ and σ → ππ within the accepted theoretical framework for non leptonic D decays. We also review the linear sigma model, finding that it gives a description which is consistent with the experimental data.

Two quark-meson soliton models — the Linear Sigma Model and the Chromodielectric Model — are used to describe the nucleon and delta excitation. Treating the delta as a bound state, we obtain its electroproduction amplitudes corrected for recoil effects.

The effect of different forms of relativistic spin coupling of constituent quarks on the nucleon electromagnetic properties is studied. The correlations between the static observables are independent of the shape of momentum part of the nucleon light-front wave function. The neutron charge form factor also depends on different choices of spin coupling schemes, for a given magnetic moment. The scalar quark pair is preferred by the neutron charge form factor data for momentum transfers below 1 (GeV/c)², independent of the shape of the wave function.

Based on the many phenomenological models appearing in the QHD literature we propose a general theoretical framework which, after a proper choice of mathematical parameters, is able to reproduce the results of many of those models. At the mean field level it may include all kind of meson-meson couplings. An investigation on the naturalness of the coefficients of these couplings is performed.

In the framework of the Walecka model we perform a model approximation (ρ_s = ρ), in which some nuclear matter observable are calculated analytically. The results are very close to those obtained by the original Walecka model.

We study the equation of state for neutron matter using the Walecka model including quantum corrections for baryons and sigma mesons through a realignment of the vacuum. We next use this equation of state to calculate the radius, mass and other properties of rotating neutron star.

We use the optimized linear delta expansion and functional methods to evaluate vacuum contributions in nuclear matter up to the lowest nontrivial order which includes exchange terms, and show that they are numerically very large, as predicted by the ordinary loop approximation.

Vacuum corrections in nuclear matter are evaluated on basis of the modified relativistic Hartree approximation, applied to the Walecka σ-ω model, and the relativistic Hartree approximation, employed on the non-linear model. Comparing the two approaches, we have determined the physical constraint between the compression modulus of nuclear matter and the nucleon effective mass. Moreover, the results in our work suggest we can find, for same pairs of these quantities, additional physical roots for the quartic order scalar meson self-coupling parameter of the non-linear treatment.

One of the most important applications of nuclear matter models is the study of neutron stars. Since such objects are essentially bound by gravity, it is advisable to take into account the space-time curvature in such models. The problem is that the usual derivation of Einstein equation from a Lagrangian density (or scalar) uses the implicit (and unnoticed) assumption that there are no fermions in the system. This is obviously unacceptable for nuclear matter. In this work, we show a possible solution to this problem.

The effect of the medium in the coupling constants implicate in a charge symmetry breaking on nuclear interactions. The amount of energy due to this modification can explain the Nolen-Schiffer anomaly.

Variational methods suitable for relativistic nuclear problems are investigated. Numerical variational solutions of the Walecka model in the Hatree approximation are discussed.

We develop a consistent treatment for hot and flowing asymmetric nuclear matter. Using the mean-field theory (MFT), predictions of the σ – ω Walecka model at finite temperature are compared with the corresponding results of the Zimanyi-Moszkowski and the non-linear models. The statistical theory of grand-canonical potentials is incorporated to the formalism. We also describe the behavior, at finite temperature, of the asymmetric and flowing nuclear matter. As an application, we describe bulk properties of neutron and protoneutron stars by considering the Tolman-Oppenheimer-Volkoff (TOV) equations.

In the framework of a model recently developed by the authors, it is here shown that both and distributions in the proton can be consistently described by considering its pionic fluctuations alone. Predictions of the model closely agree with the last experimental data of the E866 Collaboration.

We have applied the Meson Cloud Model to calculate inclusive momentum spectra of pions and kaons produced in high energy proton-proton collisions. For the first time these data are used to constrain the cloud cut-off parameters, and we discuss the relative strength of the πN and πΔ vertices. We also have described the E866 data on and from the nucleon sea.

We apply the Meson Cloud Model to the calculation of nonsinglet parton distributions in the nucleon sea trying to identify possible sources of SU(3) flavor breaking. We find that the existing SU(3) flavor asymmetry in the nucleon sea can be quantitatively explained by the meson cloud…

We discuss the possibility of the asymmetry in D^-/D⁺ production, from π^- beams, being a direct consequence of the properties of the light quark fragmentation function into heavy mesons. The main features of the asymmetry, as a function of x_F, are easily described.

We study the Lorentz structure and other properties of the gluon correlator from where all lower twist gluon distributions can be obtained. These functions are then organized in a matrix in the gluon-nucleon spin space, where their physical significance is more transparent. Bounds on these functions are also derived.

We analyze the dependence of the loop model results for the strange–quark observables on the NYK* form factors and couplings. We find, in particular, that the now generally favored soft NΛK* form factors can reduce the magnitude of the K* contributions in such models by more than an order of magnitude, compared to previous results with hard form factors. We also discuss some general implications of our results for hadronic loop models.

We discuss the three-dimensional φ⁶ theory in the context of the 1/N expansion at finite temperature. We use the method of the composite operator (CJT) for summing a large set of Feynman graphs. We analyze the behavior of the thermal square mass and the thermal coupling constant.

In this work we use theoretical results from QCD with simple concepts of quantum mechanics like WKB approximation in order to determine the effective masses of bound states of quark - antiquark (mesons). The local approximation of Schrödinger's equation is suggested in the study of light mesons. We also use some QCD results in calculation of cross sections that, as the effective masses, connect experimental data with theoretical results.

The following sections are included:

• Introduction

• Field Theory On A Momentum Hyperboloid

• The Dyson-Schwinger Equation

• Discussion and Remarks

• References

The light-front (LF) quantization of QCD in light-cone (l.c.) gauge is discussed. The Dirac method is employed to construct the LF Hamiltonian and theory quantized canonically. The Dyson-Wick perturbation theory expansion based on LF-time ordering is constructed. The framework incorporates in it simultaneously the Lorentz gauge condition as an operator equation as well. The propagator of the dynamical ψ₊ part of the free fermionic propagator is shown to be causal while the gauge field propagator is found to be transverse. The interaction Hamiltonian is re-expressed in the form closely resembling the one in covariant theory, except for additional instantaneous interactions, which can be treated systematically. Some explicit computations in QCD are given.

The so-called conformal affine Toda theory coupled to the matter fields (CATM), associated to the ŝl(2) affine Lie algebra, is studied. The conformal symmetry is fixed by setting a connection to zero, then one defines an off-critical model, the affine Toda model coupled to the matter (ATM). Using the "dressing" transformation method we construct the explicit forms of the two-soliton classical solutions, and show that a physical bound soliton-antisoliton pair (breather) does not exist. Moreover, we verify that these solutions share some features of the sine-Gordon (massive Thirring) solitons, and satisfy the classical equivalence of topological and Noether currents in the ATM model. We show, using bosonization techniques that the ATM theory decouples into a sine-Gordon model and a free scalar. Imposing the Noether and topological currents equivalence as a constraint, one can show that the ATM model leads to a bag model like mechanism for the confinement of the "color" charge inside the sine-Gordon solitons (baryons).

In the present work we give a closed expression for the quantum correction to the soliton mass in two-dimensional scalar field theory models. We show that in order to get a finite expression, after renormalized, the phase shift δ(p) will behave as 1/p for large p. We then solve for the solitonic solutions in the model.

We discuss a system formed by two pairs of brane-anti-brane that form an arbitrary angle in a plane. We identify the gauge groups from this system which presumably could be used to construct gauge theories…

LIST OF PARTICIPANTS