Elastic peak and hadron size from at-channel viewpoint

A consistent approach for understanding hadron size and the elastic diffraction peak from at-channel viewpoint is presented. Our approach is orthogonal to that of ans-channel additive quark model. We consider the problem of determining the elastic amplitude as the shadow of multiparticle production in the framework of dual topological unitarization (DTU), when pion exchanges are included in addition to the usual vector-tensor exchanges which generate the Pomeron. The inclusion of pion exchange does not affect the Pomeron trajectory substantially, but plays an important role in the computation of Pomeron residues to external particles. Good agreement with elastic data as well as total cross sections is obtained.     

Can a pomeron be really “supersoft”?

The low energy J/gf photoproduction cross-section has been studied on the basis of the Pomeron model. To incorporate the discrepancy between experimental data and predictions by conventional models, i.e. the sum of the soft Pomeron with intercept 1.08 and the hard Pomeron with intercept 1.418, a Regge trajectory associated with a scalar meson (f,a) exchange which we call “supersoft” Pomeron, is introduced additionally. To distinguish between the conventional model and this new additional Pomeron, observations related to other polarization observables in upcoming polarized experiments are discussed.     

The two-pion exchange NN potential in nuclear matter and nuclear stability

A meson exchange model of the ππ interaction which fits free ππ scattering data is used to calculate the interactions of pions in nuclear matter as a function of nuclear density. Polarization of the nuclear medium by the pions results in a marked increase in the s-wave ππ attraction at low energy. The influence of this effect on the nucleon-nucleon interaction is a corresponding increase with density of the NN central potential due to the exchange of two correlated pions, resulting in an NN interaction which fails to saturate. A possible mechanism for restoring the theoretical stability of nuclear matter is explored and found to be effective.     

Meson-exchange currents in pion-nucleus double-charge-exchange reactions

The scattering of pions by virtual mesons in the nuclear medium is analysed and its contribution to the process of double-charge exchange in pion-nucleus scattering compared to the conventional mechanism which involves charge exchange in the scattering of the pions with two different nucleons. It is shown that at forward angles the cross section is decreased by about 50% around pion energies T ≈ 130 MeV and increased by a similar amount at energies above the resonance, T ≈ 250 MeV. At large angles the meson-exchange contribution changes the cross section appreciably and can become the dominant mechanism.     

Investigation of the parton structure of pomeron in b \bar b-pair double-Pomeron-exchange production on the CMS (LHC)

Production of b $\bar b$ -pairs in the process of hard double-Pomeron exchange (DPE) of protons has been studied on the CMS plant at the LHC accelerator energies of $\sqrt s = 7$ TeV. The method for estimation of valent parton contribution in the Pomeron structure is developed. On the basis of H1 (DESY) data for parton distributions in Pomeron the calculations were performed to predict the hard (valent) parton components in the Pomeron structure. The contribution of valent partons is estimated about 61%. Using program package CMSSW, the event reconstruction of studied process also was made. This method can be applied to the available experimental data from the CMS detector.     

Reggeon field theory: Formulation and use

We formulate and discuss Reggeon field theory, which enables one to systematically analyze the exchange of Regge poles and associated branch points in high energy hardron scattering. The field theory is first motivated by a consideration of hybrid Feynman graphs, and then a more general derivation from crossed-channel multiparticle unitarity relations is given. Rules for Reggeon interaction and propagation are formulated. We treat in some detail the problem of the Pomeron or vacuum pole which has α(0) = 1 and is responsible for diffractive processes. In particular the renormalization group analysis of Reggeon field theory is presented and the structure of Pomeron partial wave amplitudes is elucidated. Also the question of Pomeron or absorptive corrections to secondary trajectories (both fermion and boson) is considered. We make some comments on important problems yet remaining in Reggeon field theory; in particular, we stress the study of its s-channel content.     

Some tests for the helicity structure of the Pomeron in ep collisions

We discuss the reaction ep→epp?X in the onephoton exchange approximation, where it is in essence the reaction γ*p→p?X. A large rapidity gap is required between the particle or particles of the proton remnant pJ and those of X. We define a suitable azimuthal angle between a leptonic and a hadronic plane. The dependence of the cross section on is given explicitly and can be used to extract cross sections and interference terms for the reactionγ*p→p?X corresponding to the various helicities of the virtual photon γ*. The interference terms can be used to test models for the large rapidity gap events in a sensitive way. We discuss in detail models with factorizing Pomeron exchange and in particular the Donnachie- Landshoff Pomeron model. We make some remarks on soft colour exchange models and on possible effects of QCD background vacuum fields. We conclude with a suggestion to look for Odderon exchange in exclusive deep inelastic high energy reactions like γ*p→,p?π⁰and ?p→p?η.     

Interference of secondary pions and time-space characteristics of their emission volume in π− p interactions at 40 GeV/c

The interference of positive and negative pions produced in π^? p interactions at 40 GeV/c is studied. It is shown that negative pions are emitted from larger distance than positive ones. The influence of resonance production on the size of pion emission volume is observed.     

High Energy Proton-Proton Elastic Scattering in the Pomeron Exchange Model

We study high energy proton-proton elastic scattering in the framework of Pomeron exchange model. The cross section of the process are calculated without any free parameters. Our finding is that Pomeron exchange theory gives perfect fits to total cross section at the energy of√s higher than 10 GeV and to differential cross section at the momentum transfer [t] less than 1.5 GeV2. For total cross section at lower energy √s ＜ 10 GeV and differential cross section at larger momentum transfer region of |t| ＞ 1.5 GeV2, the Pomeron exchange theory needs to be improved.     

High Energy Proton-Proton Elastic Scattering in the Pomeron Exchange Model

We study high energy proton-proton elastic scattering in the framework of Pomeron exchange model. The cross section of the process are calculated without any free parameters. Our finding is that Pomeron exchange theory gives perfect fits to total cross section at the energy of √(s) higher than 10 GeV and to differential cross section at the momentum transfer |t| less than 1.5 GeV². For total cross section at lower energy √(s)<10 GeV and differential cross section at larger momentum transfer region of |t|>1.5 GeV², the Pomeron exchange theory needs to be improved.     

Multiple-Pomeron splitting in QCD—A novel antishadowing effect in coherent dijet production on nuclei

We discuss the salient features of the Pomeron splitting mechanism for coherent diffraction of pions into hard dijets on nuclei. Our findings include antishadowing multiple-Pomeron splitting expansion for diffractive amplitudes, exact cancellation of nuclear attenuation, and broadening/antishadowing effects to leading twist and parameter-free perturbative calculation of nuclear-rescattering-driven higher twist correction. We comment on the pQCD interpretation of the E791 results on diffractive dijets.     

Photoproduction of φ mesons from protons and deuterons with linearly polarized photons at LEPS/SPring-8 experiment

Diffractive photoproduction of φ mesons near threshold involves Pomeron exchange, pseudoscalar exchanges and possible exotic components such as glueball and scalar-meson exchange. We measured φ-meson photoproduction from protons and deuterons at forward angles by using linearly polarized photons with E _γ = 1.5–2.4 GeV. The decay asymmetries show dominance of the natural-parity exchange process. The energy dependence of cross sections will help in determining the behavior of the Pomeron exchange near threshold. Correspondence: W. C. Chang, Institute of Physics, Academia Sinica, Taipei 11529, Taiwan     

f-Dominance of the Pomeron in Reggeon Field Theory

A Reggeon Field Theory (RFT) which incorporates the Pomeron and thef-pole is presented. The constrains on the renormalization group β-functions imposed by thef-dominance of the Pomeron are derived. We show that these constrains are satisfied by the RFT at least up to third order in the coupling constants.     

Behaviour of the proton-proton total cross section at ISR energies in the reggeon calculus

We study the behaviour of σ^pp_T at ISR energies in the Reggeon calculus with a bare triple Pomeron coupling non vanishing at q² = 0. The parameters are determined from elastic and inclusive data. A sizable increase of σ_T with s can only be obtained when the bare Pomeron intercept is such that the renormalized Pomeron singularity is above one, in the forward direction.     

A model for the high energypp and¯pp diffraction scattering

The high energy elasticpp and¯pp scattering is studied within the framework of a specific model for the diffractive background. The double Pomeron exchange as well as secondary trajectory contributions are properly taken into account. The total cross section, the phase of the forward amplitude and the angular distribution are computed and compared with the existing experimental data.     

High-energy scattering in a two-dimensional gauge theory

We study high-energy scattering in two-dimensional quantum chromodynamics in the 1/N_colour expansion. To first order, high-energy forward scattering amplitudes are power-behaved with the factorization, signature and exchange degeneracy properties found in dual Regge models. Backward scattering has deviations from naive quark power-counting rules which are related to the form factor and “Regge” behaviours. In the second order of 1/N_colour vacuum exchange diagrams do not give a new Pomeron singularity, but do break exchange degeneracy.     

BFKL Pomeron in the reaction γ ⊥ * (Q 2)p→ρ ⊥ 0 p at large Q 2 and W

The reaction γ _⊥ ^* (Q ²)p→ρ _⊥ ⁰ p has been studied at large Q ² and W ²/Q ² and low momentum transfers to the nucleon, k _⊥ ² —that is, in the region where the Pomeron exchange mechanism is operative. At sufficiently large Q ², the Pomeron interacts with quarks occurring at small distances, whereby the hard component of the Pomeron is separated, so that the process is governed by the Pomeron of perturbative QCD (BFKL Pomeron). Our calculations indicate that, in vector-meson electroproduction at low k _⊥ ² , the perturbative regime cannot set in fast because, for Q ²≤100 GeV² and, accordingly, for W ²/Q ²≤10⁷, comparatively large distances of $\rho _{q\bar q} > 0.2$ fm are important.