Bare Pomeron Research Articles

Fluctuations, saturation, and diffractive excitation in high energy collisions

Diffractive excitation is usually described by the Good--Walker formalism for low masses, and by the triple-Regge formalism for high masses. In the Good--Walker formalism the cross section is determined by the fluctuations in the interaction. In this paper we show that by taking the fluctuations in the BFKL ladder into account, it is possible to describe both low and high mass excitation by the Good--Walker mechanism. In high energy $pp$ collisions the fluctuations are strongly suppressed by saturation, which implies that pomeron exchange does not factorise between DIS and $pp$ collisions. The Dipole Cascade Model reproduces the expected triple-Regge form for the bare pomeron, and the triple-pomeron coupling is estimated.

A More Restrictive Upper Bound for the Bare Pomeron Intercept

By studying the properties of the modified Gribov-Levin-Ryskin evolution equation which incorporates both shadowing and antishadowing effects, the more restrict upper bound is set for the bare pomeron intercept in the case when gluons uniformly distribute within the proton.

SUPERCRITICAL POMERON AND EIKONAL REPRESENTATION OF THE DIFFRACTION SCATTERING AMPLITUDE

The intercept of the supercritical pomeron is examined with the use of different forms of the scattering amplitudes of the bare pomeron. The one-to-one correspondence between the eikonal phase and the ratio of the elastic and total cross-section is shown. Based on new experimental data of the CDF collaboration, the intercept and power of the logarithmic growth of the bare and total pomeron amplitude are analyzed. It is shown that as a result of the eikonalization procedure, the bare QCD pomeron becomes compatible with experiment.

Observation of high energy quark-antiquark elastic scattering with mesonic exchange

We studied the high energy quark-antiquark elastic scattering with an exchange of a mesonic state in the t channel with −t/Λ QCD 2 a ̊ 1 . Two methods are proposed to eliminate the strong background from bare pomeron, reggized gluon and odderon exchange. The feasibility of measuring mesonic reggeon exchange is discussed.

Pomeron and odderon in high energypp and $$p\bar p$$ elastic scattering

High energypp and\(p\bar p\) data on elastic scattering and total cross sections are analyzed in a model including the pomeron, odderon and secondary reggeons. A dipole model is used for the pomeron and for the odderon. By construction, our (bare) pomeron ansatz produces a single dip, as observed experimentally. The model reproduces the logarithmically rising cross sections with a unit pomeron intercept, but better fits are obained when a small non-zero value of the parameter δ = αp (0) is allowed for. Predictions for the future accelerators (UNK, LHC, SSC) are given.

Deep-inelastic events containing a measured jet as a probe of QCD behavior at small x.

We examine the proposal that deep-inelastic ({ital x},{ital Q}{sup 2}) scattering events which contain an identified jet, with transverse momentum squared {ital k}{sup 2}{congruent}{ital Q}{sup 2}, allow an ideal determination of the QCD behavior at very small {ital x}. We solve the Lipatov equation to predict the shape of the jet spectrum in such events and show that measurements at the DESY {ital ep} collider HERA should be able to verify, inter alia, whether the gluon indeed has the theoretically anticipated {ital g}{similar to}{ital x}{sup {minus}{alpha}}{sub {ital P}} small-{ital x} behavior with the intercept {alpha}{sub {ital P}} of the bare perturbative QCD Pomeron possible as large as 1.5.

Cross sections of high-energy hadron interactions in LLA QCD

Total, total elastic and diffraction dissociation cross sections of\(pp(\bar pp)\) interactions are calculated in the leading logarithmic approximation of QCD in the energy region\(\sqrt s = 0.05 - 200TeV\) accounting for absorption effects at the quark level. Our calculations with very large intercept of bare pomeron (Δ>1/2) are in qualitative agreement with the data; however, we predict comparatively large cross section of double-diffraction dissociation.

The pomeron as an expanding grey disk

In the crossing symmetric Reggeon calculus based on the 1N expansion, s-channel unitarity sum rules are written down explicitly to each order in 1N. Some of the lowest order sum rules are shown to imply a non-vanishing bare triple-Pomeron coupling at t = 0, irrespectively of the bare Pomeron intercept.

Possible parametrization of parton distributions

The gluon and quark distributions of the nucleon are evaluated using the Altarelli-Parisi equations with the input distributions at Q ∘ 2=5GeV 2 for sea-quarks and gluons modified by the factor (ax −0.6+b). The new parametrization incorporates singular small-x behaviour implied by bare Pomeron in QCD and provides consistent with large-x experimental data results as well. The theoretical predictions relevant for HERA for structure functions in the region of very small x (10 −4 <x<10 −2) and large Q 2 and for the cross-section σ(γ ∗ p→ψ X ) are presented.

The shrinkage of the diffraction peak of the bare pomeron in QCD

The new parameterQ0 is introduced in our integration over transverse momentaqt in perturbative QCD to avoid infrared divergencies. Consideringqt>Q0, the distribution of wee partons in impact parameter (bt) and the mean radius of interaction are calculated in the framework of the leading logarithmic approximation (LLA) of perturbative QCD. It is shown that the slope of the elastic amplitude increases as\(B \propto {{\sqrt {\alpha _s In s} } \mathord{\left/ {\vphantom {{\sqrt {\alpha _s In s} } {Q_0^2 }}} \right. \kern-\nulldelimiterspace} {Q_0^2 }}\).

Bare pomeron in perturbative QCD and small x behavior of gluon distributions

The solution of the integral equation describing the bare pomeron in perturbative QCD with asymptotic freedom corrections taken into account is studied. Upper and lower bounds for the bare pomeron intercept are obtained in terms of the QCD coupling constant at some large scale. The intercept is substantially above unity. After the connection with the operator product expansion is discussed, it is shown that the behavior of parton distribution functions at small x is governed by the intercept of the bare pomeron. Thus they are steeper than 1/ x by a power of x.

An inclusive minijet cross section and the bare pomeron in QCD

An inclusive two-jet cross section is described. The energy dependence of the cross section is calculated within perturbative QCD, and related to a bare pomeron in QCD, in the region where a leading logarithmic expansion is valid.

Infrared behaviour and the bare Pomeron intercept in a Reggeon Field Theory including the Pomeron and thef-pole

An extension of the critical Reggeon Field Theory that includes both the Pomeron and thef-Reggeon fields is constructed. The quantum numbers of thef-Reggeon allows specific Reggeon-Pomeron couplings that have not been considered previously in standard works on secondary trajectories. We show the existence of a single fully stable fixed point among a total of 11 points. Unfortunately this point does not satisfy the factorization requirements imposed by thef-dominance of the Pomeron hypothesis and, in consequence, the critical Pomeron can not bef-dominated in aP+f model. We have also evaluated the value of the intercept of the bare critical Pomeron, using the method of integral representations of the propagators. The value obtained is clearly higher than the one previously obtained without thef-Pomeron interplay. With an adequate choice of the values of the bare coupling constants its value is in good agreement with the phenomenological one.

Topological Glueball Contributions to the Cylinder

Possible glueball contributions originated from the overlapping cluster configuration at the cylinder are studied in the dual topological unitarization. Two high-lying vacuum trajectories are obtained. One is the bare pomeron and the other has the same trajectory function as that of the phenomenological P'. It is argued that the result does not correspond to the cOIlventional P+ f scheme. 271 In the liNe expansion of QCD, the graph of the leading nonplanar term has a cylindrical shape with no quark loops. Color confinement hypothesis then leads us to expect the possible existence of glueballs as intermediate states in the q{j annihilation channel of this cylindrical amplitude. 1) Planar loop corrections convert the liNe cylinder into the so-called cylinder in the dual topological unitarization (DTU).2) The typical result of DTU is that the cylinder singu­ larities are obtained just through the cylinder renormalization of the planar poles. 3 ) It is improbable, however, that the insertion of quark loops extinguishes the glueball states which are inherent in the cylindrical topology. This suggests a possibility that the cylinder could generate its own singularity as a consequence of the glueball effect.4)~8) Therefore, it is important to examine whether physically acceptable pictures are realized when the cylinder retains the glueball contribution. The purpose of the present note is to investigate this problem in DTU. Especially, not only the intercept but the slope of the cylinder trajectories is examined in detail. In the following discussion, the glueball effect is intro­ duced through the overlapping cluster configuration in the s-channel cylinder discontinuity. 9) The effective random walk formalism recently proposed by Tan 10) is adopted as a calculative machinery. This formalism is fairly adequate to an investigation of the transverse structure of the multiperipheral (MP) process. Let us briefly introduce the effective random walk formalism. The standard MP integral equation for the reggeon-particle (Rp) amplitude in the J -plane reads

F-pole corrections to the critical parameters of the pomeron

A reggeon field theory with two vacuum quantum numbers Regge poles, the pomeron and the f-reggeon is presented. In such a theory only one stable fixed point appears which is sensibly different from that governing a RFT with the pomeron alone. This fact is responsible for the modifications of the critical parameters of the pomeron. In particular, the intercept of the bare pomeron increases and approaches the phenomenological value.

High-energy behaviour of a double discontinuity and the bare pomeron

Abstract The high-energy behaviour of a double discontinuity of the six-point amplitude is studied in the dual-resonance model and in a hybrid Feynman-diagram model. This discontinuity imposes, through unitarity, a bound on the intercept of the bare-pomeron singularity. It is shown that in both models the ordinary Regge trajectories which couple to two-body amplitudes decouple from the discontinuity. The origin of this decoupling is discussed. The asymptotic behaviour of the double discontinuity is controlled by sister trajectories in the dual-resonance model, and by the genuine three-particle Regge poles in a Feynman-diagram model. Insofar as the intercepts of these trajectories are lower than those of the usual Regge poles there is no strong constraint on the pomeron.

Quantum stability in Reggeon field theory: Tunneling at zero transverse dimension

The path-integral formulation of Reggeon field theory at zero transverse dimension, $D=0$, is examined. We point out the necessity of breaking the classical permutation symmetry and argue that this is accomplished by enforcing quantum stability conditions in a nonperturbative path-integral formalism. By breaking the permutation symmetry, we show that the tunneling effect for the $D=0$ theory when the bare Pomeron intercept is greater than one is not due to classical configurations; instead, tunneling comes about by a certain mixture of quantum and classical configurations. Our picture naturally leads to the instanton vacuum solution for the $D\ensuremath{\ne}0$ supercritical region advocated by White.

Bare Pomeron in four-dimensional quantum chromodynamics

Working in four-dimensional quantum chromodynamics, we solve exactly the renormalized gluon ladder at $t=0$. This approximation is obtained by reordering the perturbation expansion of the Bethe-Salpeter kernel using the renormalization group. The resulting amplitude has an accumulation of Regge poles at $j=+1$ in any gauge with gauge-fixing term $\ensuremath{-}{(2\ensuremath{\alpha})}^{\ensuremath{-}1} {(\ensuremath{\partial}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{A})}^{2}$. The existence of this singularity depends only on the short-distance behavior of the forces in the $t$ channel as given by the renormalization group. Further, this singularity couples to hadrons, and is a natural candidate for the bare Pomeron.

The bare parameters of Gribov's lagrangian in a simple t-dependent dual bootstrap model

In the context of the “ 1 N Dual Unitarization” scheme, we present an explicit dynamical study of the triple bare pomeron mechanism which governs the interaction term in Gribov's lagrangian. Together with the previously established bare pomeron slope and intercept, controlling respectively, the kinetic and mass terms in Gribov's lagrangian, this work demonstrates the viability of the “ 1 N Dual Unitarization” approach for a field theory of interaction bare pomerons.

Flavor and baryon quantum numbers and their nondiffractive renormalizations of the Pomeron

We present a theoretical review and a detailed phonomenological description of the ''flavoring'' of the bare Pomeron pole at t = 0 (i.e., the nondiffractive renormalization of its multiperipheral unitarity sum by strange quarks, charmed quarks, diquarks,...) from an ''unflavored'' intercept alpha-circumflex = 0.85 to a ''flavored'' intercept ..cap alpha.. approx. = 1.08. Experimentally, flavoring effects seem to converge rapidly; hence this number is probably close to the bare intercept of the Reggeon field theory. We treat NN, ..pi..N, and KN total cross sections and real to imaginary amplitude ratios. We do not observe oscillations. We pay particular attention to 2sigma/sub K/N - sigma/sub piN/ which rises monotonically. We present a closely related combination of inelastic diffraction cross sections which decreases monotonically, indicating that vacuum amplitudes are not simply the sum of a Pomeron pole and an ideally mixed f. In fact we argue that a Pomeron + f structure is neither compatible with flavoring nor with schemes in which flavoring is somehow absorbed away. In contrast, flavoring is required for consistency with experiment by the Chew-Rosenzweig hypothesis of the Pomeron-f identity. We close with a description of flavoring threshold effects on the Reggeon field theory at current energies.