Regge Contributions Research Articles

$D^{*}$-Meson Photoproduction off the Proton Target with the Regge Contribution

$D^{*}$-Meson Photoproduction off the Proton Target with the Regge Contribution

Photoproduction of K* meson off the proton target with the Regge contributions

We investigate the K*Λ(1116) photoproduction off the proton target by employing the treelevel Born approximation within the effective Lagrangian approach. We take into account the κ, K, and K* exchanges in the t channel in addition to the ground-state nucleon- and hyperon-pole contributions in the s and the u channels with the gauge-invariant form-factor scheme. The nucleon and the hyperon resonances, D 13(2080) and Σ*(1385), are also included. We take into account the Regge trajectories of the strange mesons for the t-channel contributions in such a way that the Feynman and Regge propagators are interpolated smoothly for the relevant photon energy region. We provide numerical results for the differential cross sections, which result in qualitatively good agreement with the presently available experimental data from the CLAS collaboration at Jefferson laboratory. The Feynman-Regge interpolation for the meson exchanges turns out to play a critical role in reproducing the data simultaneously for the low and the relatively high energy regions. We also compute the total cross sections, momentum-transfer dependence of the differential cross sections in the t-channel, and the photon-beam asymmetry as useful guides for future experiments.

Regge analysis of the ππ scattering amplitude

The theoretical predictions for the subtraction constants lead to a very accurate dispersive representation of the ππ scattering amplitude below 0.8 GeV. The extension of this representation up to the maximum energy of validity of the Roy equations (1.15 GeV) requires a more precise input at high energies. In this paper we determine the trajectories and residues of the leading Regge contributions to the ππ amplitude (Pomeron, f and ρ), using factorization, phenomenological parametrizations of the πN and NN total cross sections at high energy, and a set of sum rules which connect the high and low energy properties of ππ scattering. We find that nonleading Regge terms are necessary in order to achieve a smooth transition from the partial waves to the Regge representation at or below 2 GeV. We obtain thus a Regge representation consistent both with the experimental information at high energies and the Roy equations for the partial waves with ℓ≤4. The uncertainties in our result for the Regge parameters are sizable, but in the solutions of the Roy equations these only manifest themselves above the $K\hspace {0.03cm}\overline {\rule [0.7em]{0.6em}{0em}}\hspace {-0.8em}K$ threshold.

Λ(1520)photoproduction off a proton target with Regge contributions

We investigate the $\ensuremath{\Lambda}(1520,3/{2}^{\ensuremath{-}})\ensuremath{\equiv}{\ensuremath{\Lambda}}^{*}$ photoproduction off the proton target beyond the resonance region within a model including the Regge contributions, the tree-level diagrams with the nucleon and the certain resonance intermediate states, and one contact term. The Reggeized propagators for the $K$ and ${K}^{*}$ exchanges in the $t$ channel are employed in a gauge-invariant manner. We compute the angular and energy dependences of the cross section and some polarization observables, such as the photon-beam asymmetry and the polarization-transfer coefficients. Our results qualitatively agree with the current experimental data. We find that the Regge contributions are necessary to explain the high-energy data beyond ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}4$ GeV, especially for the angular dependences in the forward region. On the contrary, the polarization observables are insensitive to the Regge contributions due to the contact-term dominance, which is a consequence of gauge invariance. We also calculate the ${K}^{\ensuremath{-}}$-angle distribution function in the Gottfried-Jackson frame, using the polarization-transfer coefficients in the $z$ direction. We find that it owns a complicated angle and energy dependences in the forward ${K}^{+}$ scattering region.

Exclusive production of [formula omitted] pairs in γγ collisions at RHIC

We discuss exclusive electromagnetic production of two neutral ρ mesons in coherent photon–photon processes in ultrarelativistic heavy-ion collisions. The cross section is calculated in the equivalent photon approximation (EPA). Both uncertainties of the flux factors and photon–photon cross sections are discussed in detail. We show that inclusion of precise charge densities in nuclei is essential for realistic evaluations of the nuclear photon–photon cross sections. We find that the cross section, especially with realistic flux factors, is sensitive to low energy in the subsystem γγ→ρ0ρ0. The experimental data for the γγ→ρ0ρ0 cross section extracted from e+e− collisions are parametrized and used to estimate the nucleus–nucleus cross section. In addition, we include vector-dominance-model (VDM)–Regge contribution which becomes important at large photon–photon energy. Large nuclear cross sections are obtained. We discuss a possibility of focusing on the large-energy component. We find that both ρ0 mesons are produced predominantly at midrapidities and could be measured by the STAR Collaboration at RHIC.

Geodesic deviation in Regge calculus

Geodesic deviation is the most basic manifestation of the influence of gravitational fields on matter. We investigate geodesic deviation within the framework of Regge calculus, and compare the results with the continuous formulation of general relativity on two different levels. We show that the continuum and simplicial descriptions coincide when the cumulative effect of the Regge contributions over an infinitesimal element of area is considered. This comparison provides a quantitative relation between the curvature of the continuous description and the deficit angles of Regge calculus. The results presented might also be of help in developing generic ways of including matter terms in the Regge equations.

The spin and flavour dependence of high-energy photoabsorption

We review the present data on high-energy, spin-dependent photoabsorption. We find a strong isotriplet term in $(\sigma_A - \sigma_P)$ which persists from $Q^2 \sim 0.25$GeV$^2$ to high $Q^2$ polarised deep inelastic scattering. For $Q^2 \sim 4$GeV$^2$ and $x$ between 0.01 and 0.12 the isotriplet part of $g_1$ behaves as $g_1^{(p-n)} \sim x^{-{1 \over 2}}$, in contrast to soft Regge theory which predicts that $g_1^{(p-n)}$ should converge as $x \to 0$. The isotriplet, polarised structure function $2x g_1^{(p-n)}$ is significantly greater than the isotriplet, unpolarised structure function $F_2^{(p-n)}$ in this kinematic region. We analyse the low $Q^2$ photoabsorption data from E-143 and SMC and use this data to estimate the high-energy Regge contribution to the Drell-Hearn-Gerasimov sum-rule.

An interpolating mass formula and Regge trajectories for light and heavy quarkonia

Simple interpolating formula for the square of the quarkonium mass and an analytic expression for the Regge trajectories α(t) in a whole region of both light and heavy quarkonia are derived on the basis of the consideration of two asymptotics for the QCD inspired interquark potential. The leading trajectory functions obtained level off at −1 for −t→∞. This asymptotic value of α(t), α(t)⊥-−1, implies that the cross section of the form (1−x)1−2α(t), which is predicted by the triple Regge model, behaves like (1−x)3. Is this to be attributed to the behaviour of the vector meson exchange or is it some hard scattering contribution swamping the Regge contributions? The intercepts and slopes of the leading Regge trajectories αρ(t), αΦ(t), αΨ(t) and αΥ(t) are calculated.

A Study of the Reaction K-p→ϕΛ AC 4.2GeV/c

The high statistics differential cross-section, polarisation and density matrix data on K-p→ϕΛ obtained by the Amsterdam-CERN-Nijmegen-Oxford collaboration at 4.2GeV/c is analysed using a Regge pole model with evasive Regge contributions. The exchanges invoked are the K*, K**, K,KA and KZ The K*-K** exchanges are taken to be non-degenerate and a simplifying assumption on their couplings in reactions, advocated recently by Saleem and collaborators, is generalised to the present case. We do not find any need for the KB in fitting data.

Inclusive Vector Meson Production in Fragmentation Regions of Meson at Small PT

Inclusive vector meson spectra in fragmentation regions of meson at small PT are studied from a two-component model (quark fragmentation and triple Regge contributions). It is shown that our model can explain successfully various inclusive vector spectra. The analyses of this paper show that quark functions into vector mesons are nearly the same as those into pseudo-scalar mesons and the strange quark suppression factor ≃0.2, which is nearly the same as in pseudo-scalar meson production.

FESR constraint on baryonium resonances

The S, T, U resonance contribution to the p̄p FESR is an order of magnitude smaller than the ω Regge contribution. Within the duality scheme for baryoniums this would imply either a large renormalisation of the ωp̄p Regge coupling (by a factor of ≈ 3) by nonplanar unitarity effects or that there are a host of other broad baryonium states hiding in the S, T, U region. The first alternative seems to be disfavoured, however, by other phenomenological constraints.

Regge behaviour and nuclear effects: K0 regeneration on carbon

Recent very precise data on the K0 regeneration amplitude in carbon at high energy are analysed, together with lower-energy data. Their energy dependence is significantly different from that of the ω Regge exchange term in KN scattering, showing unambiguously the influence of nuclear effects at the level of a «secondary» Regge contribution. The origin of these effects is discussed within the framework of the multiple-scattering theory. From a theoretical point of view, one expects the ω-pomeron nuclear cut to lower the effective ω intercept in carbon; however, this possible qualitative explanation is not supported by qualitative calculations. A purely phenomenological analysis reveals that the effect observed is mainly due to the energy variation of the inelastic contributions to the double-scattering term.

Implications of nucleon-nucleon spin-polarization measurements

We discuss available data for spin observables in $\mathrm{pp}$ and $\mathrm{np}$ elastic scattering above 3 GeV/c. We identify those measurements which isolate exchange-amplitude components of specific interest---those which provide firm tests of Regge-exchange models and, on the other hand, those which models are unable to predict reliably. Using a simple Regge-pole-exchange model whose trajectory parameters and coupling properties are determined from data on other reactions, we compute expectations for all available $\mathrm{pp}$ spin observables and find good agreement with the data. We find that a hadronic axial-vector ${A}_{1}$-like exchange term is present in the data with strength compatible with theoretical estimates. The low-lying isoscalar exchange observed in $\mathrm{pp}$ and $\mathrm{np}$ polarization is consistent with estimates based on $\ensuremath{\epsilon}({0}^{++})$ exchange. We make a careful study of possible nonasymptotic Regge contributions which could obscure the interpretation of amplitude structure at momenta up to 6 GeV/c. We provide predictions for spin-correlation observables in $\mathrm{np}$ elastic and in $\mathrm{np}$ charge-exchange scattering.

Zweig-superconvergence relations in meson collisions

Duality is generally accepted as an important tool in our present understanding of hadron physics. Its origin can be traced back to the successful application of finite energy sum rules (FESR) to the charge exchange pion-nucleon scattering ten years ago ('). Since then the qualitative interconnections among the s-, u-channel resonances and the t-channel Regge poles is firmly established. More quanti tat ive approaches have been subsequently attempted. In particular, ADEMOLLO et al. (2) have shown how precisely the idea of duality works in meson-meson collisions (a). In these cases the resonant part of the amplitude presents no serious ambiguities. On the contrary, the Regge description of the t-channel requires a more or less arbitrary parametrization of the residue functions /~(t), somehow expoiling the striking agreement. In order to avoid this kind of uncertainties the particular type of processes having a vanishing Regge contribution has to be considered. Pioneering work in this direction had already been performed by DE ALFARO et al. (4) in the context of pseudoscalar vector meson scattering. Due to helicity arguments some of the invariant amplitudes have no t-channel exchange and a superconvergent relation (SCR) is obtained among the involved resonances parameters. Since these reactions with several vector particles are complicated by the presence of many independent amplitndcs more attention has been devoted to processes with a different type of exoticism in the t-clmnnel. Thus, many SCR have been constructed exploiting the factorization of reggeon exchanges or, more frequently, making use of arguments based on S U 3 symmetry (5). In this paper we proceed along this direction analysing the s-channel reaction r:K-~ ~K. Its t-channel is exotic since the only allowed Regge trajectory, the p-trajectory, uncouples at the 9~p vertex due to the Zweig rule. This gives rise to a new type

Structure of hadron in Migdal's regularization scheme for QCD

Migdal's approach to the spectrum of QCD is generalized to three-point (hadron) amplitudes. This procedure is shown to be unique once the two-point functions are known. In particular, meson form factors and structure functions are discussed including hard gluon and Regge contributions. Quark mass effects turn out to be very important.

Light cone, Regge contributions and large-angle scattering

The asymptotic behaviour of various three-particle vertices involving reggeons far off-mass-shell, and that of various exclusive reactions is found by using the light-cone algebra of the local and bilocal operators and supposing that the Regge contributions survive in the amplitude in the limit of large momentum transfer. The scaling behaviour (29), (34) is obtained in this way for the exclusive amplitudes. Besides, the asymptotic behaviour of hadronic form factors is obtained. The asymptotic behaviour of Regge-cut contributions and the region of applicability of the scaling behaviour (29) are found for the 2 → 2 amplitude. The relations between the dispersion contributions, Regge contributions, and those of quark diagrams, as well as the role of the signature are discussed. Predictions are given for the energy and the angular distributions for a number of two-particle reactions.

Nucleon diffractive dissociation. II. Energy dependence of the low-missing-mass cross section and constraints on triple-Regge couplings

The energy dependence of the Deck-type model is discussed and shown to be in good agreement with data on the low-mass nucleon diffractive dissociation. On the basis of finite-mass sum rules, relations between triple-Regge couplings and different Regge contributions to elastic and Deck amplitudes are obtained and duality for Reggeon-nucleon scattering amplitudes is examined. The normal two-component duality usually assumed for nondiffractive terms is found to be in contradiction with experimental data.

Helicity Poles in Five Dimensions

The Regge contribution to the six-particle amplitude is studied by going to five dimensions and considering a generalization of the usual helicity approach. This has the advantages that the Steinmann relations are satisfied in a natural way, and that there are no spurious poles. The resulting representation can also be used to study more general limits than the usual multi-Regge limit. In particular, limits relevant to the two-particle inclusive cross section can be studied. The constraints imposed on this representation by Regge factorization are also considered.

Duality Constraints on Inclusive Reactions. II. The Role of the Harari-Freund Conjecture

We present a scheme for the generalization of the two-component theory of Harari and Freund to multiparticle amplitudes and, in particular, to inclusive reactions. Our scheme is based on duality and borrows the terminology of dual perturbation theory but we do not restrict our generalizations to any specific model. We obtain a criterion for the absence of secondary (nonscaling) Regge contributions in inclusive reactions. We show how inclusive reactions may approach their limiting values from below, in contrast to total cross sections which always have positive secondary contributions. The scheme suggests a novel interpretation of diffraction dissociation which we discuss in a separate paper.

Regge cuts and high energy πN and KN scattering

A phenomenological analysis of πN and KN elastic and charge exchange scattering is made in the framework of convolutions models. The pomeron trajectory is taken with a non-zero slope which allows one to describe high-energy total cross sections (without violating the Pomeranchuk conjecture) together with d σ/d t and P o . For the Regge contribution strong exchange degeneracy and Gell-Mann's ghost killing mechanism are used. A rather good fit to the data ( σ T, d σ/d t, P o for | t| < 1.5 GeV 2/ c 2) is obtained. The slope of the pomeron is found to be the same as for pp scattering ( α′ P = 0.33 GeV −2/ c −2). In πp scattering no cut should be present in the helicity flip amplitude.