The triple regge limit of diffractive dissociation in deep inelastic scattering

We derive, within perturbative QCD, a formula for the inclusive cross section of the diffractive dissociation of the deep inelastic photon γ^*+q→X+q in the triple Regge limits?M ²?Q ²?Λ ². We use the leading ln(s/M ², ln(M ²/Q ²) approximation and derive an, expression for the triple Pomeron vertex. The Pomeron above this vertex is found to be of higher order than the BFKL Pomeron. The resulting formula for the cross section is infrared finite. We show that the Abramovsky-Gribov-Kanchelli cutting rules are satisfied, and we discuss implications for the Pomeron structure function.     

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.     

Double diffraction dissociation and test of pomeron factorization at the CERN ISR

We report the observation of double diffraction dissociation in the process p + p → (pπ⁺π^?) + X at √s of 45 GeV and momentum transfer in the ?t range 0.15?0.53 GeV² at the CERN ISR. The relative rates for elastic, single and double dissociation reactions measured here are found to agree with the prediction of Pomeron factorization.     

Improving results on transverse double spin asymmetries in the CNI region at STAR

Double spin effects in polarized pp-elastic scattering in the Coulomb nuclear interference (CNI) region are sensitive to small contributions to the nuclear amplitude in addition to Pomeron exchange dominating at high energies. Measurements of double spin asymmetries require external luminosity normalization using collision counts for all spin combinations. Several possible sources of such data from various STAR subsystems were thoroughly analyzed to make the best choice. BBC arrays were found to be free of double spin effects to the level of ～ 2 × 10^?4 thus leading to the systematic uncertainty ～10^?3 in the value of (A _NN + A _SS )/2.     

Unitarity,phenomenology, and the bare Pomeron

The possibility of utilizing the multifireball expansion and a bare Pomeron at $\text{α}\text{?}{}_{\mathrm{o}}\text{=0.85}$ as an approximation to a solution of the s-channel unitarity equations explicitly connecting 2-body and inelastic phenomenology is discussed. A scale for Pomeron renormalization effects is inferred.     

Production of thef 0 meson in the Double Pomeron Exchange reactionpp→ppπ+π−

Data are presented for the exclusive reaction pp → pp π⁺ π^? at \(\sqrt s = 62GeV\) with two leading protons at large Feynman-x and a centrally produced π^+;π^? system. In this kinematical configuration one expects a substantial contribution from Double Pomeron Exchange, which is a potential source of glueballs. The experiment was performed at the CERN ISR using the Split Field Magnet spectrometer. In the mass range between 1,000 and 1,700 MeV/c² the invariant mass distribution for the central π^+;π^? system exhibits a very significant signal for thef ⁰(1270) and no other obvious resonant states.     

Theory of interacting Pomerons

The quantitative theory of Pomeron interaction is developed on the basis of strong coupling methods and ?-expansion. The theory is consistent with all unitarity conditions. At asymptotic energy total cross section increases as (ln s)^η, the multiplicity as (lns)^η+1, and diffraction cone shrinks as (lns)^?ν, where $\text{η ≈}\text{1}\text{6}\text{, ν ≈}\text{13}\text{21}$. At modern energy the theory gives small corrections to the Regge model.     

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.     

Inclusive Pomeron-Pomeron interactions at the CERN ISR

Data are presented for the first time on inclusive Pomeron-Pomeron interactions which produce a central systemX (composed mainly of multimeson states) in proton-proton collisions at \(\sqrt s \) at the CERN ISR. The systemX has a Feynman-x distribution which is sharply peaked atx _f=0, is inconsistent with any significant contributions from Reggeon exchange processes, and has an invariant mass dependence in good agreement with the predicted formM _x ^?2 . Kaon production is about 15% of pion production, nearly independent ofM _x, while proton-antiproton production averages about 5% of pion production and increases withM _x. The structure of the central systemX develops into a jetlike shape, asM _x increases, as would be expected from a model of Pomeron fragmentation. The shape of thex _f(π) distribution in the center of mass of theX system (although not proving existence) is consistent with asoft partonic substructure of the Pomeron.     

Pomeron factorisation and the reaction γN → φN

Because of the suitability of γN → φN for studying the Pomeron, we systematically investigate the tests for Pomeron factorisation possible in this rather clean reaction, particularly from the more feasible experiment which measures the φ-density-matrix, and also an experiment measuring the recoil nucleon polarisation; the complete set of initial polarisation configurations has been considered.For any two-body parity-conserving process, a simple consequence of factorisation is M-purity which asymptotically corresponds to purely natural or purely unnatural parity in the crossed channel. Factorisation tests, therefore, include M-purity tests, but M-purity does not necessarily imply factorisation.For the φ-decay density-matrix we give all the possible factorisation tests, and show that our tests are exhaustive. A separate measurement of the recoil nucleon polarisation is shown to complement adequately the information obtained from the φ-decay density-matrix in the factorising case.For the φ-density matrix, some of the M-purity tests refer to dominant amplitudes and persist even if s-channel meson-helicity-conservation (which is experimentally true approximately) holds exactly. These tests should be easy to perform. The tests which invoke factorisation more crucially than only M-purity do not persist in that manner; these refer to the helicity nonconserving amplitudes. However, factorisation for such small amplitudes could be advantageously tested here, because of their being masked by the large amplitudes elsewhere.The factorisation tests for the φ-density-matrix can be used to distinguish a pure Regge pole type Pomeron from (a) an M-pure “cut-pole mixture” type Pomeron or an M-impure (hence nonfactorising) “cut-pole mixture” type Pomeron and also (b) a factorising “cut-pole mixture” type Pomeron or a nonfactorising “cut-pole mixture” type Pomeron. Here we have taken departure from relative reality of all amplitudes as the defining criterion for a “cut-pole mixture.” Such tests would require polarised photons and/or targets.Present γN → φN data are not adequate enough to allow firm conclusions about Pomeron factorisation, though they do indicate M-purity for the Pomeron, corresponding to pure natural parity. This is consistent with Pomeron factorisation, but M-purity is only a necessary consequence of factorisation. Better and more γN → φN data are needed to get a more complete picture of Pomeron factorisation.     

Non-diffractive Pomeron renormalization,multiplicities, and the topological expansion

The renormalization of the Pomeron due to nondiffractive K$\text{K}$, B$\text{B}$ production thresholds is considered within a simple generalization of the Chew-Rosenzweig multiperipheral realization of Veneziano's topological expansion. The results are consistent with the existence of both the “low-energy” bare Pomeron with intercept $\text{α=0.85}$ and Gribov bare Pomeron with intercept above one. The vacuum exchange part of 2σ_KN?σ_πN basically rises with energy. Qualitatively correct features of shrinkage and breaks of $\text{d}\text{σ}\text{d}\text{t}$ emerge. The multiplicity of product clusters (n) increases with energy faster than 1ns and agrees with experiment for an average number of particles per cluster of 3–4. Independently of our model the Harari-Freund multiperipheral realization of the topological expansion is shown to be in serious difficulty with multiplicities, requiring around 20 particles per cluster.     

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.     

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.     

Can φ-photoproduction easily reveal the pole-cut nature of the pomeron? Addendum to the paper “pomeron factorisation and the reaction γN - φN”

It is commonly believed that γN → ΦN is a good reaction to study the Pomeron. By considering the existing data and the various properties associated with a pole, we show that it would be experimentally hard for this reaction to reveal departures from a pole-type Pomeron. For testing factorization and relative reality of all amplitudes, our claim uses the experimentally indicated approximate s-channel meson-helicity conservation and also, almost pure nature parity in the crossed channel.     

The Pomeron and the scaling law for partial wave amplitudes

From the scaling law for the s-channel partial wave amplitudes, which guarantees simultaneously t-channel unitarity at threshold t = 4μ² and s-channel unitarity, we derive: (i) The intercept α(0) of the Pomeron is always one, if α(4μ²) > 1. (ii) The total and the elastic cross sections are bounded from below for s → ∞.

where α(4μ²) and δ(4μ²) are the position and the type of te Pomeron singularity (J ? α(4μ²))^{?1?δ(4μ2) at t = 4μ2}. (iii) The type of the Pomeron singularity δ(4μ²) is restricted: either $\text{δ(4μ}{}^2\text{) ?}\text{1}\text{2}$ or $\text{δ(4μ}{}^2\text{) ?}\text{1}\text{2}$.     

Baryon asymmetry of the proton sea at low-x

We predict a nonvanishing baryon asymmetry of the proton sea at low x. It is expected to be about 7% and nearly x-independent at x < 0.5 × 10^-3. The asymmetry arises from the baryon-antibaryon component of the Pomeron, rather than from the valence quarks of the proton, which are wide believed carriers of baryon number. Experimental study of x-distribution of the baryon asymmetry of the proton sea can be performed in ep or γp interactions at HERA, where x ～ 10^-5 are reachable, smaller than at any of existing or planned proton colliders.     

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.     

The fine structure of the Pomeron and the the slope parameter of the diffraction peak

The j plane structure of the vertex function of the Pomeron suggested by the two-pole multiperipheral model exhibits a fine structure which depends on the triple Pomeron coupling. It is found that this structure alone may explain the energy dependence of the slope parameter of the p-p diffraction peak even with an arbitrarily small slope of the Pomeranchuk trajectory.     

Light-by-light scattering in double-logarithmic approximation

In the present paper we consider the elastic \(2 \rightarrow 2\) -scattering of virtual photons at high energies in the forward kinematics at zero and non-zero values of t. Accounting for both gluon and quark double-logarithmic (DL) contributions to all orders in the QCD coupling, we obtain explicit expressions for amplitudes of this process in double-logarithmic approximation (DLA). First we keep the QCD coupling fixed and then account for running coupling effects. Applying the saddle-point method to the obtained expressions for the scattering amplitude, we calculate the high-energy asymptotics of the amplitude, which proved to be of the Regge form. The Reggeon bears the vacuum quantum numbers and therefore it is a new, DL contribution to Pomeron. Comparison of the DL Pomeron to the BFKL Pomeron shows that contribution of the DL Pomeron to the high-energy asymptotics is of the same order as contribution of the BFKL Pomeron, so the DL Pomeron should be taken into account together with the BFKL Pomeron. We estimate the applicability region for the asymptotics of the light-by-light scattering amplitude, where the the DL Pomeron can reliably represent the parent amplitude.     

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.